The History of the #Rarediseaseday Campaign in Spanish on Twitter: Longitudinal Analysis of Hashtag Use and Social Network Analysis

Abstract

Social media provides a vital arena for rare disease (RD) communities, fostering support, advocacy, and knowledge sharing. Rare Disease Day generates a large-scale online conversation, yet previous research has relied mainly on static, cross-sectional snapshots. This study captures the longitudinal evolution of the Spanish-language Twitter debate around Rare Disease Day across a fixed yearly window (1 February to 15 March) from 2008 to 2023. After filtering for Spanish-language posts, a corpus of 308,823 tweets (72,740 originals) was analyzed. We combined hashtag frequency analysis to assess topic salience with social network analysis (SNA) of co-occurrence networks to identify central thematic clusters. Results show progression from early generic expressions to increasingly deliberate, action-oriented communication, reflecting a shift towards empowered activism. A headline finding is the structural centrality and persistence of the hashtag #investigación (#research), underscoring the community’s enduring call for scientific progress. SNA further revealed the difference between transient virality—often linked to political or celebrity-driven hashtags—and the stable, identity-related topics at the core of the debate. Longitudinal hashtag analysis, particularly using SNA, provides a powerful tool to identify stable priorities of online health communities beyond transient media noise.

1. Introduction

Rare diseases (RDs), also known as uncommon or orphan diseases, comprise a heterogeneous group of conditions that, despite their low individual prevalence, collectively pose a global public health challenge. The European Union defines a rare disease as one affecting no more than 5 in 10,000 people [1], a threshold similar to that used by the World Health Organization (WHO) (no more than 1 in 2000 people) [2]. Although each condition is rare, more than 7000 different rare diseases have been identified, together affecting over 300 million people worldwide [3]. Recently, the WHO approved a resolution recognizing rare diseases as a public health priority [4].

Beyond these statistics, rare diseases impose a heavy burden on patients, their families, and health systems. These diseases are often chronic, progressive, degenerative, and potentially fatal, and are characterized by high clinical complexity and a protracted “diagnostic odyssey” that can last for years—a process which causes considerable uncertainty and distress [5]. The dispersion of affected individuals and the scarcity of expert knowledge about each rare condition further contribute to a profound sense of isolation, loneliness, and helplessness among patients and their families [6,7].

For people living with rare diseases, this sense of isolation has made community support critically important. Given their geographical dispersion and the lack of local resources, patients and families increasingly turn to online social networks as a vital environment for finding information and support [8,9]. Such digital platforms enable individuals to overcome physical barriers, connect with others who share similar diagnoses, and build virtual communities of mutual aid [10,11].

Launched in 2008 by the European Organisation for Rare Diseases (EURORDIS), Rare Disease Day (RDD) is a prominent annual initiative that harnesses social media—especially Twitter (recently rebranded as “X,” though referred to here by its original name since our data predates the change)—to unite the global RD community and raise awareness worldwide. Recognizing the importance of social media for the rare disease community [8], researchers have begun to analyze how such awareness campaigns unfold on these platforms. However, existing studies examining the RDD Twitter conversation have mostly provided static, cross-sectional “snapshots” of the discussion. For example, Hanchard et al. [12] conducted an in-depth analysis of the Rare Disease Day discourse on Twitter during a single month (February 2021), identifying different thematic orientations and networks of participating actors. While valuable, such synchronous analyses cannot capture the evolving dynamics of the campaign over time.

To date, no study has longitudinally analyzed the complete history of the Rare Disease Day conversation on Twitter since the campaign’s inception. The present work addresses this gap by examining a comprehensive dataset spanning 16 years of RDD-related tweets (2008–2023). By adopting a longitudinal perspective, we move beyond isolated snapshots to reveal long-term trends in the campaign’s online discourse. Specifically, the study pursues the following objectives:

• Trace the birth and evolution of the public conversation in Spanish on the Rare Disease Day campaign on Twitter.
• Identify changes in the dominant themes and framing strategies used by the community over time, based on the most frequently used hashtags.
• Examine the evolution of the conversation’s structure and its thematic alliances by analyzing hashtag co-occurrence patterns across the years.

In short, this work will offer a dynamic and unprecedented perspective on the construction and consolidation of a digital health movement in the Spanish-speaking world.

2. Literature Review

2.1. The Role of Social Media for the Rare Disease Community

Given the geographic dispersion of patients and the scarcity of local resources, online social networks have become a fundamental environment for the rare disease community [8]. These digital platforms enable patients and families to overcome physical distances, find others with similar diagnoses, and build virtual communities of mutual support [10,11].

These online communities are not mere discussion forums; they fulfill crucial functions that help mitigate the psychosocial impact of living with a rare disease. They offer emotional support, reduce stigma and anxiety, and facilitate the exchange of practical information on disease management, navigation of healthcare systems, and access to the latest advances in research [5,13,14].

Beyond peer support, social networks have also become powerful tools for advocacy. They allow the community to gain public visibility, organize fundraising campaigns for research, and directly engage policymakers and healthcare providers [11,15]. The capacity for mobilization and coordination provided by these digital platforms has been key to patient empowerment, helping to transform patients from passive recipients of care into active agents in managing their health and driving social change [10].

2.2. The Networked Structure of Rare Disease Advocacy

The rare disease advocacy movement is characterized by a networked organizational structure. Because patient associations for specific rare diseases are often small and resource-limited, they frequently join together under larger “umbrella” federations that amplify their voice and coordinate collective efforts. In the Spanish-speaking world, each country has its own rare disease organizations, and these groups collaborate through national or regional alliances. In Spain, for instance, the Spanish Federation of Rare Diseases (FEDER) represents the interests of over 400 individual RD associations, acting as their voice and serving as an interlocutor with government institutions. Similar national federations exist in other Spanish-speaking countries (including FADEPOF in Argentina, FEMEXER in Mexico, FECOER in Colombia, FECHER in Chile, FEPER in Peru, FEPPER in Paraguay, FERPOF in Ecuador, FEVEPOF in Venezuela, and the Costa Rican Federation of Rare Diseases).

At the broader regional level, the European Organisation for Rare Diseases (EURORDIS), founded in 1997, is an alliance of patient organizations that leads rare disease advocacy across Europe and was the original initiator of Rare Disease Day. In Latin America, the Ibero-American Alliance for Rare, Orphan, and Uncommon Diseases (ALIBER), established in 2013, similarly works to strengthen the community’s voice across Spanish-speaking countries. This multi-level organizational framework—from local associations up to international alliances—is mirrored in the digital sphere as well. Federations such as FEDER serve as hubs connecting multiple actors online, while alliances like EURORDIS and ALIBER act as bridges linking national conversations with the global debate, thereby facilitating the transnational dissemination of campaigns and information. The significance of these hubs is reflected in their social media reach: as of August 2025, the Twitter account of FEDER (@FEDER_ONG) had approximately 38,992 followers, EURORDIS (@eurordis) had about 31,490, and NORD (@RareDiseases, the U.S. counterpart to EURORDIS) had around 39,872 followers.

2.3. Twitter as a Data Source for Health Research

Social media has not only transformed the patient experience but also opened up new opportunities for health research. Among these platforms, Twitter has proven especially valuable as a data source due to the public nature of its content, its concise text-based format, and the availability of an Application Programming Interface (API) that allows researchers to systematically collect large volumes of conversational data in real time or retrospectively [16,17].

The use of Twitter as a tool in health research is well established. A systematic review identified several key methodologies for analyzing Twitter data in health contexts, including content analysis to characterize public discourse, epidemiological surveillance (“infoveillance”) to monitor the frequency of disease-related mentions, social network analysis (SNA) to map connections between users, and engagement analysis to measure the impact of communications [17]. Researchers have applied these approaches to a wide range of topics—for example, examining trust and misinformation in vaccination campaigns [18,19] and monitoring population mental health via Twitter posts [20]. Twitter data have also been used to study crisis communication during events such as the COVID-19 pandemic [21] and to promote healthy lifestyles through public health campaigns [22,23,24].

In the specific field of rare diseases, Twitter-based research is beginning to generate valuable insights. Studies have analyzed the unmet needs of patients, the structure of support communities, and the dynamics of awareness campaigns using data from Twitter [5,8]. For instance, one study employed SNA to identify key opinion leaders within the Spanish-language rare disease Twitter network [25]. Another qualitative study examined the Twitter conversation during Rare Disease Day to discern different discursive orientations within the community [12]. These works demonstrate the feasibility and potential of Twitter for exploring communication and social interaction in the rare disease domain.

2.4. The Use of Hashtags as a Device for Framing Conversation

In the social media ecosystem—and on Twitter in particular—the hashtag (a word or phrase prefixed with the “#” symbol) is a fundamental element. Technically, hashtags function as user-generated metadata that allow messages to be aggregated and categorized, facilitating the tracking of thematic conversations and the collection of relevant data [26]. In health-related research, hashtags have been widely used to define data corpora, identify communities of interest, and analyze public discourse around specific diseases or health campaigns [27,28].

However, the role of hashtags goes beyond simple classification. From the perspective of framing theory, hashtags can serve as powerful devices for framing online conversation. Framing theory—originally introduced by Goffman [29] and later elaborated by Entman—holds that communication is not only about transmitting information, but also about constructing meaning. Entman defines framing as the process of “selecting certain aspects of a perceived reality and making them more salient in a communicative text in such a way as to promote a particular definition of the problem, a causal interpretation, a moral evaluation, and/or a recommendation for treatment” [30].

Choosing a hashtag is not a neutral act; it is a strategic decision that emphasizes certain aspects of an issue over others, thereby guiding the audience’s interpretation [31]. For example, in the context of rare diseases, using a hashtag like #investigación (Spanish for “research”) or #ciencia (“science”) frames the problem as a scientific challenge that requires additional funding and resources for research and development. In contrast, a hashtag such as #equidad (“equity”) frames the issue as one of social justice and human rights, calling for equitable access to diagnosis, treatment, and care. A study of the #BRCA hashtag in a cancer community [32] demonstrated how patient communities leverage such hashtags to construct collective narratives, challenge dominant medical discourses, and reframe the conversation about health from their own perspective.

Thus, a longitudinal analysis of the most frequently used hashtags in a campaign over time is not merely a list of popular terms, but rather a means of tracking the evolution of the movement’s strategic frames. A shift in dominant hashtags from one year to the next may signal a change in community priorities—for instance, moving from initial “awareness” messages to more complex frameworks centered on “political action,” “rights,” or “therapeutic innovation.” Examining hashtag co-occurrence networks further allows us to map the community’s evolving networks of meaning, revealing how conceptual alliances form at each point in time [28,33].

2.5. The Rare Disease Day Campaign

Launched by EURORDIS in 2008, Rare Disease Day is an international campaign held annually on the last day of February (28 February, or 29 February in leap years, the “rarest” date) to raise awareness of rare diseases. The campaign’s main goal is to broaden public understanding of rare diseases and to engage key stakeholders—including policymakers, healthcare authorities, the pharmaceutical industry, researchers, and health professionals—in order to promote actions that improve the lives of patients and their families.

Since its inception, Rare Disease Day has rapidly expanded worldwide. The first edition in 2008 was observed in 18 European countries, and by 2009, it had gone global with the involvement of the U.S. National Organization for Rare Disorders (NORD) and patient groups on other continents. Spanish-speaking countries joined gradually and were instrumental in consolidating the campaign in the Spanish-speaking world. Spain officially participated starting in 2009, alongside Panama, Colombia, and Argentina in that year. In subsequent years, additional nations came on board: Mexico, Peru, and Uruguay in 2011; Chile, Costa Rica, Guatemala, and Venezuela in 2012; Cuba, Ecuador, and Paraguay in 2014; Bolivia in 2015; and the Dominican Republic in 2019 (according to the campaign’s official records).

From the outset, the campaign has had a strong digital component. The official website https://www.rarediseaseday.org (accessed on 20 August 2025) centralizes resources, defines the annual theme and slogan, and serves as a global coordination platform. Social media—particularly Twitter—has been a strategic channel for unifying the conversation through official hashtags, amplifying the reach of messages, and reinforcing a sense of belonging to a global and supportive community. The impact and volume of Rare Disease Day activity on Twitter in Spanish are especially notable, reflecting the high level of community participation, the strong engagement of Spanish and Latin American rare disease organizations, and the presence of numerous influential Spanish-language rare disease accounts on Twitter [12].

3. Materials and Methods

A retrospective capture was performed using Twitter API v2 through a “research account” capturing all tweets from the start of the Rare Disease Day campaign in 2008 until 15 April 2023. The tweets to be captured were those written in Spanish and containing any of the hashtags related to Rare Disease Day commonly used in this language.

• #diadelasenfermedadesraras
• #diadelasEERR
• #diaenfermedadesraras
• #diaEERR
• #DiaMundialDeEnfermedadesRaras
• #diamundialdelasEERR
• #diamundialenfermedadesraras
• #diamundialEERR
• #RareDiseaseDay

Messages that did not use these hashtags but did include the expressions “dia de las enfermedades raras” (rare disease day) or “dia mundial de las enfermedades raras” (world rare disease day) were also captured. Messages that used the English campaign hashtag (#rarediseaseday) were also captured, but only if the language of the tweets was Spanish, by using the Twitter API filter ‘lang:es’. The captured data were filtered to include only those tweets between 1 January and 15 March of each year.

A total of 308,823 tweets were captured, of which 72,740 were original tweets (23.6%), 229,312 retweets (74.3%), 3358 quotes (1.1%), and 3413 replies (1.1%), of which 1475 were self-replies (replies posted by the account itself, probably corresponding to threads inserted by those accounts).

This study applies a number of quantitative techniques to analyze the use of hashtags by the agents participating in the conversation in each of the global day campaigns. The analysis initially focuses on the set of hashtags that appear most frequently in original tweets (i.e., tweets created and posted directly by a user on the Twitter platform, excluding retweets, replies, and quote-tweets). To assess dissemination, the number of retweets associated with each tweet containing a given hashtag was aggregated. Section 4 compares the hashtags most frequently proposed in original tweets with those most widely disseminated by the community through retweets. The analysis was conducted using the Python programming language (v3.12.10; Python Software Foundation, Wilmington, DE, USA), in combination with the Pandas library.

For a more formal analysis of the conversation about Rare Disease Day, an analysis of hashtag co-occurrence was performed. Social network analysis (SNA) [34] techniques were employed to examine hashtag co-occurrence networks and identify the most relevant terms in each campaign, using the software Gephi (v0.10.1; Gephi Consortium, Paris, France). Kendall–Theil–Sen regression [35,36] was then applied to detect terms that significantly gained or lost relevance over time. The study was carried out using the kendalltau and theilslopes functions from the scipy.stats Python library, v1.16.1. In addition to identifying key hashtags and their temporal dynamics, communities of hashtags were detected using the Louvain clustering algorithm [37] implemented within the Gephi software, allowing the analysis of thematic structures and conversational domains within the network. Finally, association rules mining [38] was applied to identify the set of hashtags that most frequently co-occurred in the dataset. For this purpose, the apriori and association_rules functions from the mlxtend.frequent_patterns module, v0.23.4, in Python was used.

During the preparation of this manuscript, the author(s) used ChatGPT 4o mini (OpenAI, San Francisco, CA, USA) for getting help in the coding of the analysis scripts, ChatGPT 5 Pro for researching about the use and origin of some of the hashtags described, Gemini 2.5 Pro (Google, Mountain View, CA, USA) with deep research feature for finding related research, and NotebookLM Pro (Google Labs, Mountain View, CA, USA) https://notebooklm.google/ (accessed on 17 September 2025) for helping in analyzing and summarizing the contents of several research papers. The authors have reviewed and edited the output and take full responsibility for the content of this publication.

All Python scripts and code used for data acquisition and analysis are provided in a Supplementary GitHub repository available at: https://github.com/igarr-ule/code_-rarediseaseday_analysis (accessed on 17 September 2025).

3.1. Data Preprocessing

Prior to analyzing the data, it was preprocessed to obtain a dataset that would facilitate analysis and the drawing of conclusions. The hashtags were normalized by removing accents and converting them to lowercase letters so that they could be counted accurately. After conducting an initial exploratory analysis, it was found that some important and commonly used hashtags had different syntactic versions for the same semantic content. It was therefore decided to unify the following hashtags with a single representation, considering that they refer to exactly the same concept (see

Table 1. Unification of semantically equivalent hashtags.

Hashtags in the Dataset	Representative Hashtag
#diamundialdelasenfermedadesraras, #rarediseaseday, #rarediseasesday, #diamundialenfermedadesraras, #diadelasenfermedadesraras, #diaenfermedadesraras, #diadelaser, #diadelaseerr, #diamundialer, #diamundialeerr, #diamundialdeenfermedadesraras	#diamundialdelasenfermedadesraras
#enfermedadespocofrecuentes, #enfermedadesminoritarias, #enfermedadespococomunes, #eerr, #rarediseases, #enfermedadesraras, #enfermedadeshuerfanas	#enfermedadesraras
#28defebrero, #28febrero, #28f, #28feb	#28defebrero
#29f, #29feb, #29defebrero, #29febrero	#29defebrero
#covid19, #covid_19, #covid_19, #covid19, #covid19, #covid	#covid19

). Singular hashtags were kept as they are, as they could refer to a particular disease and not to the set of diseases as a whole.

Hashtags are represented in their original Spanish version; refer to

Table A1. Hashtags appearing in the dataset and possible equivalent English versions.

Hashtag as Appearing in Dataset	Possible Equivalent English Hashtag
#AcidosisTubular	#TubularAcidosis
#AcidosisTubularRenal	#RenalTubularAcidosis
#AlgoRaroSeMueve	#SomethingRareMoves
#AndresIniesta8	#AndresIniesta8 (the name of a Spanish football player)
#Apoyo	#Support
#Apture	#Apture
#becker	#Becker
#BlogPbP	#BlogPbP (blog about evidence-based pediatrics)
#BusFobiaM4	#BusPhobiaM4
#CaixaForum	#CaixaForum
#CambiameChallenge	#ChangeMeChallenge
#CedoMiNombre	#ILendMyName
#ChavezInmortal	#ImmortalChavez
#Ciencia	#Science
#Compartido	#Shared
#ComparteTusColores	#ShareYourColors
#ConFuerzaGanamosTodos	#WithStrengthWeAllWin
#coronavirus	#coronavirus
#Coruna	#Coruna (A Coruña, a city in the north-west of Spain)
#Coslada	#Coslada (A village near Madrid, Spain)
#CreandoRedesDeEsperanza	#BuildingNetworksOfHope
#Cuba	#Cuba
#CubaPorLaSalud	#Cubaforhealth, #cubasupportshealth
#CubaPorLaVida	#CubaForLife
#Cuidado	#Care
#covid19	#covid19
#Diagnóstico	#diagnostic
#Día	#day
#DíaDeAndalucia	#AndalusiaDay
#DiaEnfermedadesRaras	#rarediseaseday
#DíaDeLasEnfermedadesRaras	#rarediseaseday
#DíaDeLasER	#RDDay (Rare Disease Day)
#DíaDeLasEERR	#RDDay (Rare Disease Day)
#DíaMundial	#WorldDay
#DíamundialDeEnfermedadesRaras	#WorldRareDiseasesDay
#DíamundialDeLasEnfermedadesRaras	#WorldRareDiseasesDay
#DíamundialDeLasEERR	#WorldRDday (World Rare Disease Day)
#DíamundialEPOF	#WorldRDday (World Rare Disease Day)
#DíaMundialER	#WorldRDday (World Rare Disease Day)
#DíaMundialEERR	#WorldRDday (World Rare Disease Day)
#DíaMundialEnfermedadesRaras	#WorldRareDiseasesDay
#DiferentesPeroIguales	#DifferentButEqual
#Discapacidad	#Disability
#DM2020	#WY2020 (WorldYear2020)
#Duchenne	#Duchenne
#EBP	#LPV (meaning Low Prevalence Disease)
#Educación	#education
#EERR	#RRDD (Rare Diseases)
#enfermedad	#disease
#enfermedades	#diseases
#EnfermedadesMetabólicas	#MetabolicDiseases
#EnfermedadesMinoritarias	#MinorityDiseases
#EnfermedadesPocoComunes	#UncommonDiseases
#EnfermedadesPocoFrecuentes	#InfrequentDiseases
#EnfermedadesRaras	#RareDiseases
#EnfermedadRara	#RareDisease
#EnfermedadesHuérfanas	#OrphanDiseases
#Enfermería	#nursing, #nurse
#EnVideo	#invideo, #onvideo
#EPOFArgentina	#RDArgentina (Rare Diseases Argentina)
#Equidad	#Equity
#ER	#RD (Rare Disease)
#Er2012	#RD2012
#Esoll	#Esoll
#España	#Spain
#Esperanza	#Hope
#Europa	#Europe
#FASGA	#FASGA (name of a union)
#FASGASocialConLasER	#FASGASocialWithRD
#fb	#fb (facebook)
#Febrero	#February
#Febreroraro	#RareFebruary
#Febreroraro2020	#RareFebruary2020
#FECHER	#FECHER (name of a Chilean RD federation)
#FEDER	#FEDER (name of the Spanish RD federation)
#FelizDíaDeAndalucía	#HappyAndalusiaDay
#FelizDomingo	#HappySunday
#FelizJueves	#HappyThursday
#FelizLunes	#HappyMonday
#FelizMartes	#HappyTuesday
#FelizMiércoles	#HappyWednesday
#FelizSábado	#HappySaturday
#ff	#ff (#followfriday)
#FFPaciente	#FFPatient (#followfridaypatient)
#Gracias	#Thanks (#ThankYou)
#GuardiaCivilPHG	#GuardiaCivilPHG (The Guardia Civil is Spain’s national gendarmerie, a military force charged with police duties. PHG = Hutchinson-Gilford Progeria)
#HazlasVisibles	#MakeThemVisible
#HazlasVisiblesECI	#MakeThemVisibleECI (ECI = “El Corte Ingles”, spanish stores
#hcsmla	#hcsmla (Healthcare Social Media Latinoamérica)
#HiperinsulinismoCongénito	#CongenitalHyperinsulinism
#HipersinulinismoCongénito	#CongenitalHypersinulinism (same as above but with a typo)
#HipertensiónPulmonar	#PulmonaryHypertension
#Hoy	#Today
#iEnterateQue	#FindouTthat
#IluminaPorLasEnfermedadesRaras	#LightupForRare
#Investigación	#research
#InvestigarEsAvanzar	#ResearchIsProgress
#JuntosSomosMás	#TogetherWeAreMore
#kts	#kts
#leyenfermedadesraras	#rarediseaselaw, #lawforrarediseases
#LightupForRare	#LightupForRare
#LosPacientesImportan	#PatientsMatter
#Madrid	#Mmadrid
#ManoAManoConER	#HandInHandWithRD
#ManyStrongProud	#ManyStrongProud
#MmedicamentosHuerfanos	#OrphanDrugs
#MeetTheUnmet	#MeetTheUnmet
#MejorEsPosible	#BetterIsPossible
#MostráTusRayas	#ShowYourStripes
#MuchosFuertesOrgullosos	#ManyStrongProud
#Mundo	#World
#MundoMetabólico	#MetabolicWorld
#MyLeaf	#MyLeaf
#Nieve	#Snow
#Ninos	#Children
#NiTanRaras	#NotSoRare
#nomamar	#nomamar (Mexican slang)
#noticias	#news
#nuestraphelanita	#ourphelanita (referring to Phelan–McDermid syndrome)
#OTDirecto28F	#OTLive28F
#PacientesQueCuentan	#PatientsThatMatter
#Pasapalabra20aniversario	#Pasapalabra20thanniversary
#phelanmcdermid	#phelanmcdermid
#PideUnDeseo	#MakeAWish
#PocoFrecuente	#infrequent
#PodríasSerTú	#ItCouldBeYou
#raras	#rare (plural)
#RarasNoInvisibles	#RareNotInvisible
#raredisease	#raredisease
#rarediseaseday	#rarediseaseday
#rarediseaseday2015	#rarediseaseday2015
#rarediseaseday2018	#rarediseaseday2018
#rarediseaseday2020	#rarediseaseday2020
#rarediseaseday2021	#rarediseaseday2021
#rarediseaseday2022	#rarediseaseday2022
#rarediseaseday2023	#rarediseaseday2023
#rarediseases	#rarediseases
#rarediseasesday	#rarediseasesday
#RaroEsIgnorar	#ItsRareToIgnore
#rss	#rss
#sabiasque	#didyouknow
#salud	#health
#sanchezmentiroso	#sanchezliar
#sanidad	#healthcare (#publichealth)
#SíALaInclusión	#YesForInclusion
#SindromeKlippelTrenaunay	#KlippelTrenaunaySyndrome
#SinCienciaNoHayFuturo	#NoScience_NoFuture
#SíntomasDeEsperanza	#SymptomsOfHope
#SKT	#KTS (#KlippelTrenaunaySyndrome)
#solidaridad	#solidarity
#SomosFEDER	#WeAreFEDER
#SomosVisibles	#WeAreVisible
#SOSEnfermedadesRaras	#SOSRareDiseases
#SoyFueraDeLoComún	#IAmOutOfTheOrdinary
#SoyRaro	#IAmRare
#StopAME	#stopSMA (Spinal Muscular Atrophy)
#telemaraton	#telethon
#TiempoAFfavor	#TimeInOurFavor
#Titular	#Headline
#TodosSomosRaros	#WeAreAllRare
#UnaSonrisaPocoFrecuente	#AnInfrequentSmile
#UnClicUnaEstrella	#OneClickOneStar
#UnaEnfermedadRaraEs	#ARareDiseaseIs
#unmilagroparaabraham	#amiracleforabraham
#UnJuevesDiferente	#ADifferentThursday
#uv_rtl23	#uv_rtl23 (a hashtag for a group of students communicating on Twitter while working on an assignment)
#Venezuela	#Venezuela
#VicentedelBosque	#VicentedelBosque
#visibilidad	#visibility
#wtf	#wtf
#VIIIEncuentroNacionalER	#VIIINationalMeetingRD
#YoTambien	#MeToo (not related to the famous hashtag related to female abusing)
#ZolGenSMA	#ZolGenSMA
#24hEERR	#24hRD (24 h for Rare Diseases)
#28f	#feb28, #28feb
#28feb	#feb28, #28february
#28febrero	#february28
#28defebrero	#28thoffebruary
#29f	#feb29, #29feb
#29feb	#feb29, #29february
#29febrero	#february29
#29defebrero	#29thoffebruary
#366dDíasDeEERR	#366DaysOfRD

in Appendix A for a translation into a possible equivalent English hashtag if needed. In the following sections, a translation to English will be provided, as well as the first time the hashtag appears.

3.2. Ethical Considerations

This research was conducted in line with ethical approval granted by the Research Ethics Committee of the Health Service of Castilla y León (SACYL), Spain, on 25 November 2020, under approval number: 20183. All data analyzed were publicly available tweets, collected via Twitter’s Application Programming Interface (API) in compliance with its developer agreement and privacy policy after obtaining the status of a research account. We ensured that no personal identifiable information was shared, with exceptions for public organizations or public figures acting in a public capacity, as well as news editors.

4. Results

The total number of unique accounts that participated throughout the campaigns was 145,343, of which 37,308 participated by creating original tweets. Figure 1 shows the number of unique accounts that participated during the different years in the conversation around Rare Disease Day. The highest number of participants was reached in 2018, with a total of 26,320 accounts participating with at least one tweet (of any type) in the campaign. In the same year, the number of accounts that posted at least one original tweet also peaked at 4821.

Original tweets are particularly relevant for analysis as they reflect the topics of interest that participating users want to highlight and disseminate voluntarily on the network. The hashtags used in this type of message represent these topics and the content to be transmitted.

Figure 2 shows the evolution of the number of original tweets and retweets for each year of the campaign. Retweets are the most direct way to spread a message and are by far the most important type of interaction in the captured data. By studying the most retweeted hashtags, we can see what types of messages and topics were most widely disseminated in each campaign.

The total number of unique hashtags used in all campaigns was 14,566. Figure 3 shows the evolution of this value. It can be seen that, until 2019, there was a continuous increase in the number of hashtags used, especially in 2017, 2018, and 2019, followed by a trend toward stability at around 2700 unique hashtags per year.

The dataset obtained provides a complete narrative of the conversation during the different Rare Disease Day campaigns, and allows analyzing the evolution of the most relevant and widely discussed topics in each year. The results obtained from the analysis of the hashtags used in the dataset captured over the different years are presented below. The study period has been divided into different intervals according to the degree of maturity observed in the conversation.

4.1. Initial Years: 2008 to 2010

The first tweet mentioning Rare Disease Day (without using any hashtag) was created in 2008 by the Chilean publication La Tercera with the text “Celebran el Día de las Enfermedades Raras en Europa” (“Celebrating Rare Disease Day in Europe”). It is the only tweet captured that year. In 2009, 10 accounts participated, all creating at least one original tweet. Only the tweet created by the Spanish Federation for Rare Diseases (FEDER) was shared through a single retweet, which was the only interaction registered that year. In 2010, participation increased to 86 unique accounts. Hashtags appeared in some of the tweets for the first time (the hashtag had been incorporated as a native feature on Twitter on 1 July 2009), but only four different hashtags were used in total, and none mentioned the celebration of Rare Disease Day.

4.2. Years of Growth: 2011 to 2013

Table 2. Most used hashtags in original tweets and retweets, from 2011 to 2013.

Year	Hashtags in Original Tweets		Hashtags in Retweets
2011	#diamundialdelasenfermedadesraras	42	#salud	161
	#salud	36	#diamundialdelasenfermedadesraras	30
	#diferentesperoiguales	21	#acidosistubularrenal	18
	#acidosistubular	20	#enfermedades	15
	#acidosistubularrenal	17	#acidosistubular	14
	#enfermedades	13	#diferentesperoiguales	13
	#enfermedadesraras	11	#enfermedadesraras	11
	#fb	10	#blogpbp	5
	#noticias	9	#raras	5
	#blogpbp	7	#educacion	5
	#nomamar	6	#hcsmla	3
	#caixaforum	4	#unmilagroparaabraham	3
	#wtf	4	#enfermeria	3
	#dia	3	#compartido	3
	#raras	3	#hipertensionpulmonar	2
2012	#diamundialdelasenfermedadesraras	343	#diamundialdelasenfermedadesraras	334
	#enfermedadesraras	108	#enfermedadesraras	213
	#salud	52	#europa	58
	#29defebrero	45	#29defebrero	55
	#enfermedades	31	#raras	54
	#hiperinsulinismocongenito	26	#salud	50
	#hipersinulinismocongenito	18	#hiperinsulinismocongenito	48
	#noticias	18	#hipersinulinismocongenito	44
	#envideo	17	#ninos	26
	#fb	16	#er2012	21
	#raredisease	16	#apture	20
	#rss	15	#envideo	19
	#ninos	13	#dia	18
	#europa	12	#enfermedades	17
	#wtf	12	#diamundial	15
2013	#diamundialdelasenfermedadesraras	503	#diamundialdelasenfermedadesraras	760
	#enfermedadesraras	114	#enfermedadesraras	148
	#salud	57	#hoy	90
	#enfermedades	33	#salud	61
	#28defebrero	32	#raredisease	55
	#raredisease	24	#enfermedades	48
	#pideundeseo	22	#unjuevesdiferente	33
	#ienterateque	20	#28defebrero	28
	#coslada	17	#coslada	27
	#unjuevesdiferente	17	#vicentedelbosque	22
	#noticias	15	#esoll	21
	#discapacidad	14	#apture	21
	#leyenfermedadesraras	14	#ff	19
	#diadeandalucia	12	#raras	17
	#sabiasque	12	#noticias	17

shows the most frequent hashtags in original tweets and the most retweeted hashtags for the given year. The numbers indicate the number of times each hashtag appears in original tweets or in retweets, respectively.

The first time the main hashtag for Rare Disease Day appeared in a tweet written in Spanish was on 21 February 2011, using the English version (#rarediseaseday). The first appearance of the hashtag in its Spanish version (#DiadelasEnfermedadesRaras) was on the 24th of that same month and was inserted by the same account as the previous one: a user in Mexico.

In 2011, there was a notable increase in participation in Rare Disease Day, although participation remained limited during that year and the following two: 2012 and 2013. During this period, the hashtags used were very generic, not really aimed at conveying an idea about the RD community, and those promoted by early users or groups of users interested in a particular rare disease usually stood out.

It is worth noting that in 2011 and 2012, some tweets from Latin American countries included hashtags expressing sarcasm and disbelief about the existence of a world day for rare diseases, using hashtags like #nomamar or #wtf, which gives an idea of the general public’s lack of awareness of this health issue at that time.

In 2013, two phenomena that are common in the use and dissemination of hashtags on Twitter can be observed. The hashtag #Leyenfermedadesraras (#rarediseaseslaw) was one of the most used in original tweets that year. It was created to call for a rally in the Plaza de Armas in Santiago, Chile, demanding a specific law for people affected by rare diseases (the Chilean law on rare diseases was finally passed in 2025). The hashtag was used 14 times in 14 original tweets but did not achieve sufficient dissemination to be one of the most widely used hashtags, probably because the 14 messages were created by only two Chilean users who, despite mentioning different accounts to achieve greater dissemination, only received 13 retweets in total.

The second most relevant phenomenon this year was the dissemination achieved by the hashtag #VicentedelBosque, which, despite not appearing in the list of the most used hashtags in original tweets (in fact, it only appeared in two original tweets), managed to position itself as one of the hashtags with the most retweets of the year, probably because of being a very popular figure (coach of the Spanish national soccer team that had just won the Euro Cup in 2012) and because one of the original tweets was posted by HOLA! magazine, which had a large number of followers on the platform.

4.3. Years of Consolidation: 2014 to 2018

Table 3. Most used hashtags in original tweets and retweets, from 2014 to 2018.

Year	Hashtags in Original Tweets		Hashtags in Retweets
2014	#diamundialdelasenfermedadesraras	1188	#diamundialdelasenfermedadesraras	2750
	#enfermedadesraras	375	#enfermedadesraras	604
	#28defebrero	87	#educacion	356
	#salud	66	#investigacion	304
	#educacion	62	#visibilidad	301
	#esperanza	58	#cuidado	277
	#ff	50	#telemaraton	210
	#enfermedades	37	#28defebrero	143
	#investigacion	31	#ff	124
	#todossomosraros	27	#esperanza	115
	#visibilidad	24	#enfermeria	72
	#diadeandalucia	21	#diadeandalucia	63
	#cuidado	19	#enfermedades	58
	#podriassertu	19	#podriassertu	57
	#raras	18	#todossomosraros	55
2015	#diamundialdelasenfermedadesraras	1938	#diamundialdelasenfermedadesraras	6489
	#hazlasvisibles	1110	#hazlasvisibles	5096
	#raroesignorar	451	#enfermedadesraras	768
	#enfermedadesraras	257	#raroesignorar	700
	#28defebrero	122	#fb	685
	#somosvisibles	93	#28defebrero	242
	#salud	79	#soyfueradelocomun	219
	#mundo	73	#hazlasvisibleseci	190
	#hazlasvisibleseci	68	#manoamanoconer	121
	#manoamanoconer	68	#algorarosemueve	120
	#algorarosemueve	47	#infografia	85
	#rarediseaseday2015	43	#stopame	78
	#alicante	41	#alicante	74
	#fecher	39	#rarasnoinvisibles	68
	#rarasnoinvisibles	30	#rarediseaseday2015	67
2016	#diamundialdelasenfermedadesraras	2437	#diamundialdelasenfermedadesraras	7000
	#somosfeder	521	#enfermedadesraras	1698
	#enfermedadesraras	480	#somosfeder	1611
	#cedominombre	254	#cedominombre	666
	#29defebrero	245	#29defebrero	493
	#yotambien	103	#investigacion	332
	#salud	57	#yotambien	289
	#skt	55	#fb	261
	#enfermdedadesraras	54	#guardiacivilphg	147
	#kts	54	#apoyo	140
	#sindromeklippeltrenaunay	54	#stopame	127
	#enfermedades	36	#todossomosraros	123
	#infografia	27	#undiacomohoy	84
	#hazlasvisibles	25	#coruna	82
	#28defebrero	24	#24heerr	63
2017	#diamundialdelasenfermedadesraras	4417	#diamundialdelasenfermedadesraras	18,981
	#enfermedadesraras	469	#enfermedadesraras	2501
	#somosfeder	319	#fb	1650
	#investigacion	221	#somosfeder	1618
	#28defebrero	167	#investigacion	1253
	#unasonrisapocofrecuente	123	#er	468
	#felizmartes	102	#unasonrisapocofrecuente	460
	#diadeandalucia	67	#28defebrero	365
	#salud	60	#raredeseaseday	209
	#confuerzaganamostodos	52	#espana	186
	#andresiniesta8	35	#felizmartes	178
	#mundometabolico	35	#myleaf	154
	#busfobiam4	33	#enfermeria	152
	#cambiamechallenge	31	#sialainclusion	136
	#enfermedadesmetabolicas	24	#confuerzaganamostodos	131
2018	#diamundialdelasenfermedadesraras	4822	#diamundialdelasenfermedadesraras	31,023
	#enfermedadesraras	906	#enfermedadesraras	6102
	#somosfeder	206	#investigacion	1189
	#showyourrare	195	#showyourrare	1169
	#pocofrecuente	192	#somosfeder	1093
	#investigacion	180	#rarasnoinvisibles	838
	#felizdiadeandalucia	162	#hazlasvisibles	619
	#28defebrero	153	#28defebrero	583
	#salud	134	#pocofrecuente	559
	#felizmiercoles	132	#rarediseaseday2018	527
	#nieve	116	#ffpaciente	516
	#hazlasvisibles	106	#medicamentoshuerfanos	429
	#rarediseaseday2018	87	#felizmiercoles	426
	#diadeandalucia	71	#phelanmcdermid	302
	#otdirecto28f	66	#nuestraphelanita	297

shows the most frequent hashtags in original tweets and the most retweeted hashtags for the specified year during this period.

During this period, the use of Twitter as a means of conversation around Rare Disease Day became consolidated. The growth of users creating original tweets increased steadily, and the participation of unique accounts also grew significantly, especially in 2017 and 2018. During these first stages, we can indirectly observe how users began to include Twitter as one of the platforms where they could have a presence and create messages aimed at the community. At that time, the most used social network was Facebook, and we can see how users began to reproduce content created on this social network on Twitter. The hashtag #FB appears as relevant in both original tweets and within the most widely shared ones, which is a sign of this type of practice. The Facebook platform allowed users to create posts with a much larger number of characters than Twitter, so a common practice was to create the message on that platform and then refer to it on Twitter by linking to the original Facebook post. Also, during these years, the hashtag #FF, which stands for “Follow Friday,” also became popular on Twitter and was used to recommend interesting accounts on the platform on that day of the week.

Below, some of the most popular hashtags for each year within this period are shown, along with a comment about their origin and use.

4.3.1. Year 2014

This year saw the first clear appearance of hashtags related to generic concerns and needs of people with rare diseases: #educación, #investigación, #visibilidad, #cuidado (in English, #education, #research, #visibility, #care), ranking among the top hashtags both in terms of the number of original tweets containing them and in the list of most retweeted hashtags of the campaign. It is noteworthy that one of these hashtags, #investigación, continued to appear regularly among the top retweeted in all subsequent years, despite the appearance of hashtags designed specifically for the World Day campaign.

The hashtag #telemaraton (#telethon) was created by Spain’s main public television channel for a special show devoted to raising funds for rare diseases. Although the hashtag was not among the most used in original tweets, it was among the most retweeted.

The hashtag #TodosSomosRaros (#WeAreAllRare) was promoted by the user community in 2014, probably adapting it from the slogan “Todos somos raros, todos somos únicos” (“We are all weird, we are all unique”) created jointly by the Isabel Gemio Foundation, FEDER, and the ASEM Federation for the Spanish television telethon held that year.

The hashtag #PodríasSerTú (#ItCouldBeYou) is a hashtag created by the user community and widely disseminated this year.

4.3.2. Year 2015

The 2015 Rare Disease Day campaign can be considered as the one that achieved maturity in the way of conveying messages specifically related to the celebration of this event, as well as in the use of hashtags designed and aimed at conveying a message or idea to the general public.

#HazlasVisibles (#MakeThemVisible) was the hashtag promoted by FEDER this year. It is the first hashtag to call for action and therefore represents a milestone on Twitter in the field of communication on Rare Disease Day. Its success is such that it appears in second place on the list of hashtags with the most retweets, standing out above the hashtag #enfermedadesraras, which had occupied this position in previous years. Related to this one, the hashtag #HazlasVisiblesECI was promoted by the Spanish department store El Corte Inglés (ECI), supporting FEDER’s initiative to popularize the slogan “make them visible” this year.

The hashtag #RaroEsIgnorar (#ItsRareToIgnore) was promoted in 2015 from Chile by the Chilean Federation of Rare Diseases (FECHER) as part of the first “Expo de Enfermedades Raras” (Rare Diseases Expo) and in commemoration of Rare Disease Day. It was the third most used hashtag in original tweets and the fourth most retweeted hashtag that year.

The hashtag #soyfueradelocomun (#IAmOutOfTheOrdinary) was promoted by the Spanish trade union FASGA (now called Valorian), which is active in the department store sector (it was founded in El Corte Inglés). Despite having little presence in original tweets, it managed to rank among the most retweeted of that year.

The campaign carried out in Venezuela to mark this year’s World Day promoted the hashtag #ManoAManoConER (#HandInHandWithRD). While #HazlasVisibles was used in Spain, #ManoAManoConER was promoted in Venezuela with the same objective: to raise awareness and visibility about the reality of people living with a rare disease.

The hashtag #AlgoRaroSeMueve (#SomethingRareMoves) was promoted by FEGEREC (Galician Federation of Rare and Chronic Diseases). It was used in conjunction with the main hashtag for the campaign in Spain (#HazlasVisibles), especially in tweets originating in Galicia.

The hashtag #RarasNoInvisibles (#RareNotInvisible) is particularly relevant, as its use goes beyond the celebration of Rare Disease Day. This hashtag seems to have emerged from the user community in late 2014 and quickly gained widespread acceptance. FEDER used it in a tweet on 15 January 2015. It has been used over time with fairly high acceptance and emphasizes the need to raise awareness of these types of conditions, coinciding with the officially promoted hashtag #HazlasVisibles.

This hashtag may have been inspired by the “Raras pero no invisibles” (rare but not invisible) project, led by the Malaga-based science communication agency Sombradoble, which began in 2013. The initiative was publicized through a crowdfunding campaign launched on 13 May 2013 to produce a documentary about rare diseases. This initiative led to the creation of the “Raras pero no invisibles” platform, which continues to raise awareness about rare diseases through various means, including the Twitter account @NoInvisibles, one of the most important accounts for creating and disseminating content about rare diseases in Spain.

In Chile, the hashtag #SomosVisibles (#WeAreVisible) was promoted by a patient association that sent out more than 90 tweets mentioning different accounts to spread their message, achieving their goal of widespread dissemination. Once again, the need to raise awareness of these diseases was emphasized. Also in Chile this year, as previously mentioned, the Chilean Federation of Rare Diseases (FECHER) promoted the use of the hashtag #RaroEsIgnorar.

#StopAME (#stopSMA) was promoted by a number of users to raise awareness of spinal muscular atrophy (SMA, AME in Spanish) and was widely disseminated despite not appearing among the most common hashtags in the original tweets that year. Something similar happened with this same hashtag the following year 2016.

4.3.3. Year 2016

The initiative and associated hashtag #CedoMiNombre (#ILendMyName) were promoted in Spain by the Institute for Research on Rare Diseases (INDEPF) as part of this year’s Rare Disease Day celebrations. The campaign had a significant impact on social media, mainly on Twitter, encouraging users to change their profile name to that of a rare disease for the day.

This year, the Spanish federation FEDER started promoting the hashtag #SomosFEDER (#WeAreFEDER) as a sign of identity and belonging for the associations registered with the federation and as a way of affirming its support for the associative movement and the federation of associations.

The hashtag #YoTambien (#MeToo) was part of an initiative promoted by Papás Blogueros (Blogging Dads) and Madresfera (Mothersphere), which raises awareness of content related to parenthood. On 29 February 2016, they launched a “blogging carousel” to raise awareness of rare diseases and asked people to publish and share the campaign using the hashtag #yotambién.

The hashtag #GuardiaCivilPHG was used in an original tweet by the Spanish Civil Guard (the Guardia Civil is Spain’s national gendarmerie, a military force charged with police duties), which joined the #CedoMiNombre campaign by choosing Hutchinson-Gilford Progeria (PHG in Spanish) as the rare disease to which it would lend its name. Despite only posting one original tweet with this hashtag, it became one of the 15 most retweeted of the year.

4.3.4. Year 2017

The hashtag #UnaSonrisaPocoFrecuente (#AnInfrequentSmile) was created and promoted in Spain by the Institute for Research on Rare Diseases (INDEPF). The campaign consisted of encouraging people to share a photo of themselves smiling on social media using this hashtag. The main objective was twofold: on the one hand, to raise awareness of people living with a rare disease and, on the other, to humanize the cause through a gesture as universal and positive as a smile.

The Isabel Gemio Foundation (a non-profit organization that promotes scientific research into muscular dystrophies and other rare diseases) designed and promoted the hashtag #ConFuerzaGanamosTodos (#WithStrengthWeAllWin), which was a relevant hashtag both in the original tweets and in the dissemination it achieved.

The hashtag #MyLeaf was promoted by the initiative “Raras pero no invisibles” (rare but not invisible) to raise awareness of the “My Leaf” app, developed by the authors of the initiative themselves and used to share data on rare diseases. According to the authors, its objective is “to use technology to learn more about diseases, how they affect people, and thus advance knowledge in a collaborative way, involving patients, families, caregivers, researchers, and doctors.”

4.3.5. Year 2018

Hashtags #nuestraphelanita and #phelanmcdermid refer to Phelan–McDermid syndrome. They gained widespread attention thanks to a tweet by a famous Spanish comedian.

This year’s global campaign promoted the use of the hashtag #ShowYourRare as part of the global campaign for Rare Disease Day. Under the slogan “Show your rare. Show you care”, the initiative invited people around the world to paint their faces in bright colors, take a photo or video, and share it on social media with the hashtag #ShowYourRare. The aim was to create a high-impact global visual campaign to show solidarity and support for the rare disease community, urging politicians, researchers, companies, and healthcare professionals to take action. This hashtag ranked among the top tweets and retweets during the 2018 and 2019 campaigns.

The hashtag #FFpaciente (#FFPatient) was created and promoted in 2015 by a Spanish nurse who is very active on social media, creating digital health content. The initiative arose with the idea of adapting the popular Twitter hashtag #FollowFriday (or #FF), which was used on Fridays to recommend accounts to follow. This user added the word “patient” to create a space where, every Friday, the voices and experiences of patients in the field of health could be highlighted and given visibility. Over time, what began as a personal initiative on Twitter evolved into the FFPaciente Association, established in 2018 as a non-profit organization that continues the work of empowering patients and improving communication in the healthcare environment. The hashtag was used on Twitter in various campaigns for Rare Disease Day promoted by the user community. It achieved widespread coverage in the 2018, 2019, and 2020 campaigns, ranking among the most retweeted hashtags despite not appearing among the most used in original tweets in any of them.

#MedicamentosHuérfanos (#OrphanDrugs) was a hashtag that appeared in a single original tweet from the @NoInvisibles account, but given the relevance of this account, it spread thanks to community action. The tweet in question gave visibility to an infographic on the topic of rare diseases created by another user.

The hashtag #FelizDíaDeAndalucía has been used regularly for several years. This hashtag refers to the celebration of the day of the Autonomous Community of Andalusia in Spain, which is celebrated on 28 February. Many tweets from users and associations in this autonomous community include this hashtag as a way to also commemorate this event.

4.4. Years of Maturity: 2019 to 2023

Table 4. Most used hashtags in original tweets and retweets, from 2019 to 2023.

Year	Hashtags in Original Tweets		Hashtags in Retweets
2019	#diamundialdelasenfermedadesraras	4675	#diamundialdelasenfermedadesraras	21,701
	#enfermedadesraras	1692	#enfermedadesraras	11,364
	#somosfeder	1187	#somosfeder	10,123
	#juntossomosmas	949	#juntossomosmas	8081
	#28defebrero	239	#showyourrare	1604
	#showyourrare	218	#28defebrero	943
	#investigacion	143	#febreroraro	836
	#felizjueves	122	#investigacion	671
	#salud	112	#ffpaciente	520
	#febreroraro	77	#espana	408
	#feder	75	#soyraro	399
	#duchenne	58	#rarasnoinvisibles	372
	#becker	56	#felizjueves	320
	#rarasnoinvisibles	48	#gracias	249
	#enfermedades	45	#salud	222
2020	#diamundialdelasenfermedadesraras	3312	#diamundialdelasenfermedadesraras	19,284
	#enfermedadesraras	856	#enfermedadesraras	3776
	#enfermedadrara	243	#enfermedadrara	1321
	#somosfeder	234	#somosfeder	1282
	#29defebrero	160	#fasgasocialconlaser	833
	#fasgasocialconlaser	121	#29defebrero	801
	#investigacion	85	#fasga	483
	#fasga	84	#febreroraro2020	461
	#salud	81	#rarediseaseday2020	432
	#rarediseaseday2020	72	#unaenfermedadraraes	416
	#febreroraro2020	69	#investigacion	400
	#dm2020	66	#dm2020	304
	#diamundialepof	63	#viiiencuentronacionaler	222
	#mostratusrayas	63	#366diasdeeerr	199
	#epofargentina	55	#ffpaciente	196
2021	#diamundialdelasenfermedadesraras	3845	#diamundialdelasenfermedadesraras	22,616
	#enfermedadesraras	1093	#enfermedadesraras	5791
	#28defebrero	238	#sanchezmentiroso	1365
	#somosfeder	205	#sintomasdeesperanza	1330
	#rarediseaseday2021	199	#28defebrero	1250
	#investigacion	126	#rarasnoinvisibles	1217
	#sintomasdeesperanza	117	#rarediseaseday2021	1076
	#covid19	96	#somosfeder	810
	#salud	64	#covid19	767
	#hipertensionpulmonar	61	#felizdomingo	663
	#felizdomingo	53	#investigacion	603
	#enfermedadrara	49	#zolgensma	546
	#raredisease	46	#investigaresavanzar	391
	#rarasnoinvisibles	44	#andalucia	385
	#febreroraro	38	#pasapalabra20aniversario	381
2022	#diamundialdelasenfermedadesraras	3202	#diamundialdelasenfermedadesraras	14,918
	#enfermedadesraras	1099	#enfermedadesraras	4778
	#28defebrero	244	#28defebrero	1133
	#investigacion	130	#rarediseaseday2022	734
	#rarediseaseday2022	121	#investigacion	627
	#compartetuscolores	76	#sosenfermedadesraras	497
	#salud	76	#compartetuscolores	281
	#nitanraras	72	#nitanraras	277
	#ebp	44	#lightupforrare	245
	#enfermedadrara	43	#sinciencianohayfuturo	236
	#iluminaporlasenfermedadesraras	39	#diadeandalucia	198
	#raredisease	35	#meettheunmet	186
	#titular	35	#salud	178
	#unclicunaestrella	33	#pacientesquecuentan	177
	#somosfeder	31	#felizlunes	172
2023	#diamundialdelasenfermedadesraras	2625	#diamundialdelasenfermedadesraras	11,638
	#enfermedadesraras	924	#enfermedadesraras	3388
	#28defebrero	210	#28defebrero	1208
	#investigacion	112	#investigacion	771
	#rarediseaseday2023	112	#cubaporlavida	563
	#salud	104	#rarediseaseday2023	484
	#tiempoafavor	78	#tiempoafavor	400
	#somosfeder	58	#mejoresposible	373
	#manystrongproud	57	#cubaporlasalud	286
	#muchosfuertesorgullosos	57	#lospacientesimportan	233
	#enfermedadrara	55	#somosfeder	227
	#diagnostico	35	#chavezinmortal	215
	#raredisease	35	#cuba	195
	#uv_rtl23	29	#enfermedadrara	195
	#lospacientesimportan	26	#raredisease	159

shows the most frequent hashtags in original tweets and the most retweeted hashtags for the specified year during this period.

4.4.1. Year 2019

The hashtag #pocofrecuente (#infrequent) was used as part of the campaign “Un Guiño #pocofrecuente por el DÍA MUNDIAL DE LAS ENFERMEDADES RARAS O POCO FRECUENTES?😉😉” (“A #infrequent wink for WORLD RARE OR UNCOMMON DISEASE DAY? 😉😉”), promoted by the Institute for Research on Rare Diseases (INDEPF) in Spain. The hashtag achieved widespread dissemination thanks to the large number of original tweets created by this institute mentioning the campaign and referring to other accounts to spread the tag.

#JuntosSomosMás (#TogetherWeAreMore) was a hashtag promoted by the solidarity platform “La Fuerza del Corazón” (The Power of the Heart), created by Spanish singer Alejandro Sanz and dedicated to collaboration and raising awareness of different social projects. The large community of followers of this platform and of the artist himself made this hashtag one of the most prominent of the year.

The hashtag #SoyRaro (#IAmRare) emerged from the user community, perhaps from its use in several original tweets from the @NoInvisibles account.

4.4.2. Year 2020

The hashtags #FasgasocialconlasER and #FASGA were promoted by the FASGA union to show solidarity with Rare Disease Day.

The hashtag #UnaEnfermedadRaraEs was promoted by the community to raise awareness of a video about rare diseases created by a Colombian YouTuber. It was widely shared on accounts in that country.

In Argentina, the hashtag #MostráTusRayas was created as the Spanish translation of the hashtag #ShowYourStripes, promoted by NORD. It appeared as one of the most used hashtags in original tweets on Argentine accounts, but it was not one of the most retweeted hashtags globally.

The hashtag #VIIIEncuentroNacionalER (#VIIINationalMeetingRD) refers to the event “National Meeting for Rare Disease Day” organized by the Spanish CREER center (State Reference Center for Care for People with Rare Diseases and their Families).

The hashtag #366DiasDeEERR (#366DaysOfRD) belongs to the challenge “366 days talking about rare diseases,” launched on 1 January 2020, by the user who created the account @MasVisibles (in November 2019), one of the most influential accounts in the field of rare diseases since its creation. This hashtag was also supported by @NoInvisibles, which contributed to its dissemination.

4.4.3. Year 2021

The only widely circulated hashtag among the most relevant ones across all the years included in the whole capture, having a direct political criticism, is #sanchezmentiroso (#SanchezLiar). This hashtag was included in a single original tweet that received over 1300 retweets, making it the hashtag with the highest reach that year, behind only the two most common and generic ones. It was created by a person with amyotrophic lateral sclerosis to denounce, in his opinion, the lack of attention to this disease by the Spanish government, and to criticize statements made by the then Prime Minister, Pedro Sánchez.

The hashtag #SíntomasDeEsperanza (#SymptomsOfHope) is the official hashtag of the campaign promoted by FEDER this year, associated with the slogan “Cada vez más personas tienen estos síntomas: la unión, la lucha y el compromiso. Son #sintomasdeesperanza” (“More and more people have these symptoms: unity, struggle, and commitment. They are #SymptomsOf Hope”).

#ZolGenSMA was a hashtag used by a pediatrician at a Mexican children’s hospital, indicating that he had received the drug of the same name and that the “era of gene therapy” was beginning.

The Spanish center CIBERER (Center for Biomedical Research in Rare Diseases) managed to position its hashtag #InvestigarEsAvanzar (#ResearchIsProgress) among the most widely used this year. This hashtag refers to the conference of the same name: “Research is Progress”. This year marked the tenth edition of the conference.

The hashtag #PasaPalabra20aniversario (#Pasapalabra20thanniversary) refers to the 20th anniversary of a cultural contest on the Spanish television channel Antena3. It was used by a couple of users in two original tweets where it was included along with the Rare Disease Day hashtag and some others, such as #covid19.

The coronavirus pandemic began in the days following Rare Disease Day in 2020, so there is no significant trace of any related hashtags from that year. However, in 2021, #covid19 does appear as one of the most relevant hashtags, both in terms of its use in original tweets and in terms of the reach it achieved. A qualitative analysis of the most widely shared tweets using this hashtag shows that the main content is (in order of reach) as follows:

• Noting and lamenting that, due to the COVID-19 pandemic, most social and health services for people with rare diseases were interrupted.
• Spreading messages of support to people affected by rare diseases in light of the added difficulties caused by the pandemic.
• Emphasizing that, without criticizing the measures and investments made to combat the pandemic, rare diseases also need attention

4.4.4. Year 2022

The official hashtag for the campaign this year, promoted by EURORDIS and supported by FEDER in Spain, was #ComparteTusColores (Spanish translation of #ShareYourColors, the official hashtag worldwide this same year). This hashtag was widely used in 2022, 2023, and 2024.

The hashtag #LightUpForRare was also promoted by EURORDIS as part of the 2022 campaign. In this case, the hashtag invited institutions, city councils, companies, and individuals to light up buildings, monuments, and homes with the official colors of World Rare Disease Day (pink, green, blue, and purple). Although the hashtag #IluminaPorlasEnfermedadesRaras was used as a Spanish translation and promoted by FEDER, and despite appearing in Spanish in a greater number of original tweets, it was not as widely used as the English version, which managed to position itself as one of the most retweeted hashtags of the event.

The hashtag #SOSEnfermedadesRaras (#SOSRareDiseases) was created by the VocesSolidarias2022 platform, which was launched in January of this same year as a community initiative to defend different causes.

In Mexico, the Accionar.io platform created the hashtag #NiTanRaras (#NotSoRare) as part of the “Nadie es Menos” (“Nobody is less”) initiative developed for this global day in 2022. It was widely promoted by accounts in that country.

The hashtag #SinCienciaNoHayFuturo (#NoScience_NoFuture) was created based on statements made by a person with different rare diseases who is very active on social media and other social networks. The hashtag was widely shared by the community.

The pharmaceutical company Sanofi created the hashtag #MeetTheUnmet, distributing it and achieving good coverage in Spain through its rare disease support project “Raras pero Reales” (on Twitter via the account @RarasReales, created in 2015 and continuing over time, it is one of the leading sources of information and awareness about rare diseases).

#Pacientesquecuentan (#PatientsThatMatter) is a hashtag used by a patient platform of the same name, which has collaborated with the Rare Disease Day campaign since 2019 and gained reach in 2022 thanks, among other things, to some of the accounts that shared its hashtag. Unfortunately, in 2023, this platform ceased its activity due to the impossibility of being managed by its creator, who was a person with chronic pain.

4.4.5. Year 2023

This year, several hashtags promoted and disseminated by accounts in Cuba and Venezuela stand out. The hashtags #CubaPorLaVida, #CubaPorLaSalud y #MejorEsPosible, (#CubaForLife, #CubaForHealth, and #BetterIsPossible) were created and promoted from original tweets by Cuban accounts promoting Rare Disease Day, which used these hashtags repeatedly. The hashtag #ImmortalChavez appeared only once in an original tweet created by a Venezuelan account, but was heavily disseminated by accounts in that country.

The hashtag #TiempoAFavor (#TimeInOurFavor) was created and promoted in Spain by FEDER for its 2023 campaign, with the slogan “Haz que el tiempo vaya a nuestro favor” (“Make time work in our favor”) explicitly asking people to use it, along with #EnfermedadesRaras and #SomosFEDER, in posts made during the campaign.

#LosPacientesImportan is a hashtag created by the Peruvian platform of the same name (“Los Pacientes Importan,” or “Patients Matter”) dedicated to giving a voice “to thousands of people with chronic, rare, and orphan diseases who seek access to and participation in Peru’s health policies.” In 2023, they were very active, generating numerous original tweets on Twitter that were widely shared.

5. Study of Hashtags Using Social Media Analysis Techniques

So far, we have described the results obtained by analyzing the most relevant hashtags that appear repeatedly in original tweets or retweets. These results give an idea of which hashtags were most used to start conversations (original tweets) and those that achieved the highest degree of dissemination (by studying retweets). However, some of these hashtags may have been promoted and used by communities that are not closely related to rare diseases, or they may belong to topics that are not closely related to the Rare Disease Day campaign.

The techniques from social network analysis (SNA) allow us to study how hashtags are related to each other, beyond simply counting the number of times they appear in tweets. In this way, we can get an idea of which hashtags are most closely related to each other in terms of the topic of rare diseases and the celebration of Rare Disease Day.

To perform this analysis, a network must be created to show the connection between hashtags. Each time two hashtags appear together in the same tweet, 1 is added to the weight of the relationship between them. By doing this each year in the entire dataset captured, a co-occurrence network of hashtags will be obtained for each of the conversations held on the corresponding campaign.

Once the co-occurrence networks for each year have been constructed, the metrics defined by social network analysis (SNA) can be calculated and interpreted to study these types of relational structures. In the case of this study, the metric known as eigenvector centrality has been used. This metric provides a measure not only of the greater or lesser number of connections a hashtag has, but also of the number of connections that the hashtags with which it is connected have. Thus, a hashtag with a high value for this metric will be relevant in terms of the number of times it appears, but it will also be relevant in terms of other important hashtags in the network to which it is related. This allows us to obtain an ordered list of the most relevant hashtags for each year. Figure 4 shows the complete network of hashtags with their relationships for the year 2023, with a total of 2448 hashtags and 17,770 relationships represented. The hashtags that are most interrelated are grouped in the densest cluster, while those that are least related to the most common ones are placed on the periphery. This effect is achieved by applying a topological distribution algorithm that considers the characteristics of the relationships between hashtags. In the case of Figure 4, the distribution has been obtained by applying the Force Atlas 2 algorithm using the Gephi software.

In Figure 5, the visualization has been filtered to show only the hashtags with the highest eigenvector centrality value. In both Figure 4 and Figure 5, the size of the node representing the hashtag (as well as the size of the font used in the node) is proportional to this centrality value.

Table 5. Most relevant hashtags each year according to the eigenvalue centrality values in the hashtag co-occurrence network.

2015	2016	2017
#diamundialdelasenfermedadesraras	#diamundialdelasenfermedadesraras	#diamundialdelasenfermedadesraras
#hazlasvisibles	#enfermedadesraras	#enfermedadesraras
#enfermedadesraras	#somosfeder	#investigacion
#28defebrero	#cedominombre	#28defebrero
#raroesignorar	#investigacion	#somosfeder
#rarediseaseday2015	#salud	#felizmartes
#salud	#yotambien	#diadeandalucia
#investigacion	#hazlasvisibles	#salud
#enfermedades	#creandoredesdeesperanza	#venezuela
#fb	#felizlunes	#unasonrisapocofrecuente
#algorarosemueve	#sanidad	#confuerzaganamostodos
#raras	#apoyo	#solidaridad
#diadeandalucia	#esperanza	#ciencia
#diagnostico	#todossomosraros	#feder
#hazlasvisibleseci	#madrid	#diamundial
2018	2019	2020
#diamundialdelasenfermedadesraras	#diamundialdelasenfermedadesraras	#diamundialdelasenfermedadesraras
#enfermedadesraras	#enfermedadesraras	#enfermedadesraras
#28defebrero	#28defebrero	#29defebrero
#investigacion	#investigacion	#investigacion
#salud	#showyourrare	#salud
#showyourrare	#somosfeder	#felizsabado
#somosfeder	#felizjueves	#somosfeder
#rarediseaseday2018	#salud	#rarediseaseday2020
#diadeandalucia	#febreroraro	#febreroraro2020
#rarasnoinvisibles	#feder	#dm2020
#hazlasvisibles	#enfermedades	#enfermedadrara
#feder	#enfermedadrara	#enfermedades
#enfermedadrara	#soyraro	#366diasdeeerr
#felizdiadeandalucia	#ffpaciente	#visibilidad
#diamundialdelasenfermedadesraras	#raredisease	#coronavirus
2021	2022	2023
#diamundialdelasenfermedadesraras	#diamundialdelasenfermedadesraras	#diamundialdelasenfermedadesraras
#enfermedadesraras	#enfermedadesraras	#enfermedadesraras
#28defebrero	#28defebrero	#28defebrero
#rarediseaseday2021	#investigacion	#investigacion
#investigacion	#rarediseaseday2022	#salud
#somosfeder	#salud	#rarediseaseday2023
#salud	#raredisease	#enfermedadrara
#felizdomingo	#enfermedadrara	#somosfeder
#febreroraro	#enfermedades	#diagnostico
#hipertensionpulmonar	#febreroraro	#tiempoafavor
#covid19	#visibilidad	#raredisease
#enfermedades	#hipertensionpulmonar	#enfermedades
#buenosdias	#compartetuscolores	#febrero
#raredisease	#feder	#colombia
#esperanza	#rarasperonoinvisibles	#equidad

shows the main hashtags sorted by this centrality value for each year between 2015 and 2023.

Looking at the results obtained by studying these networks for each campaign, relevant differences can be highlighted with respect to the data obtained by analyzing only the number of times the hashtag appears in the original tweets and the retweets that were presented previously.

Several of the hashtags that appear most frequently in original tweets or in the list of most widely disseminated tweets occupy very low positions in these lists based on relevance according to the eigenvector: #Telemaraton, #sanchezmentiroso, #PasaPalabra20Aniversario, #CubaPorLaVida, #CubaPorLaSalud, #MejorEsPosible, because they are found not to be connected to hashtags that are relevant to the community as a whole. For example, #sanchezmentiroso ranks, in 2021, in position 1676 out of 2887 (58.1st percentile), with a normalized eigenvector of 0.017, while #ChávezInmortal does not appear in the hashtag co-ocurrence network because the original tweet did not use any campaign hashtags (it was retrieved in the capture because it included the words “Día mundial de las enfermedades raras”)

In addition to continuing to appear as relevant, #SomosFEDER also appears in different years among the most relevant hashtags. An analysis of the tweets that include this hashtag shows that they belong to users, associations, and organizations that include this tag to mention this Spanish federation. This mention occurs organically without any explicit call to use the hashtag.

The hashtag #CreandoRedesDeEsperanza (#BuildingNetworksOfHope) appeared as relevant in 2016. This hashtag was created by the community based on the campaign slogan “creating networks of hope” promoted by FEDER that year. It is noteworthy that FEDER did not promote the slogan as a hashtag; rather, it was a spontaneous creation of the user community.

The hashtag #diagnóstico appears as one of the 15 most relevant topics in 2015 and 2023, while it only appeared as one of the most used hashtags in original tweets in 2023, but did not make it onto the list of the most retweeted hashtags of that year.

In 2020, the hashtag #coronavirus appeared as a relevant topic for the community, as it is related to other relevant hashtags in the conversation of this year. A study of the content of the tweets shows that most of them referred to complaints about the media coverage of the coronavirus compared to the attention they were giving to rare diseases during the days of world day, as well as commenting on the first cases that were appearing in different countries.

6. Hashtag Dynamics, Community Structures, and Co-Occurrence Patterns over Time

To gain deeper insights into the dataset, the analysis extended beyond the identification of the most frequent hashtags to examine their evolution and interrelationships over time. First, changes in the relevance of hashtags across different years were studied in order to highlight emerging and declining themes within the campaigns. In addition, the structure of hashtag communities was analyzed using clustering techniques, allowing the identification of groups of terms that formed thematic domains and shaped the overall conversation. Finally, associations between hashtags were explored through co-occurrence and association rule mining, which revealed patterns of terms that frequently appeared together, thus providing a more comprehensive understanding of how discourse was organized and disseminated on the platform.

6.1. Hashtag Relevance Dynamics

To examine which hashtags have shown sustained increases or decreases in relevance over the years, the Kendall–Theil–Sen test was applied.

Table 6. Hashtags with significative sustained increase in relevance.

Hashtag	Theil–Sen Slope	Kendall’s Tau	Normalized Eigenvector in 2023	Rank in 2023
#enfermedadesraras	0.039248	0.888889 ***	0.554209	#2
#investigacion	0.003364	0.611111 *	0.166411	#4
#enfermedadrara	0.003528	0.666667 *	0.105122	#7
#discapacidad	0.003107	0.611111 *	0.066308	#16
#pacientes	0.001309	0.555556 *	0.064754	#17
#diainternacionaldelasenfermedadesraras	0.003512	0.555556 *	0.035026	#178

* p < 0.05, *** p < 0.001.

and

Table 7. Hashtags with significative sustained decrease in relevance.

Hashtag	Theil–Sen Slope	Kendall’s Tau	Normalized Eigenvector in 2023	Rank in 2023
#somosfeder	−0.013755	−0.785714 **	0.094459	#8
#diadeandalucia	−0.007710	−0.642857 *	0.045756	#50
#masinvestigacion	−0.000616	−0.555556 *	0.041226	#73
#hazlasvisibles	−0.009522	−0.722222 **	0.039219	#93
#infografia	−0.002793	−0.611111 *	0.024661	#783
#blog	−0.003135	−0.714286 *	0.023088	#845
#acromegalia	−0.004031	−0.777778 **	0.021291	#940
#sindromedetourette	−0.002757	−0.714286	0.018755	#1254
#cushing	−0.003069	−0.785714 **	0.017767	#1520
#todossomosraros	−0.004308	−0.611111 *	0.001953	#2038
#mastocitosis	−0.003660	−0.777778 *	0.001863	#2059

* p < 0.05, ** p < 0.01.

present the results of this test for those hashtags where the upward or downward trend, respectively, reached statistical significance. To be included in the study, a hashtag was required to appear in at least 8 years of the analyzed period. The data used for this analysis were the eigenvector centrality values of all nodes in the hashtag co-occurrence networks of each campaign, from 2015 to 2023 (as calculated in Section 5).

Both tables display the Theil–Sen slope, which indicates the magnitude of the annual variation, while Kendall’s tau provides information on the strength and direction of this trend. In addition, the normalized eigenvector centrality value for 2023 was included to indicate the relative importance of each hashtag in the most recent year, together with its ranking based on this metric (with an eigenvector centrality value of 1 corresponding to the hashtag #diamundialdelasenfermedadesraras).

The longitudinal analysis of eigenvector centrality slopes and Kendall’s tau values highlights the consolidation of certain hashtags within the Rare Disease Day conversation. As shown in Table 6, #enfermedadesraras exhibits the steepest and statistically significant growth, confirming its role as the dominant term in the discourse, beyond the hashtag specifically dedicated to the awareness day itself (#diamundialdelasenfermedadesraras).

Some other hashtags also demonstrate statistically significant upward trajectories. The hashtags #enfermedadrara and #diainternacionaldelasenfermedadesraras, though less prominent, reinforce the linguistic and symbolic framing of the awareness campaign in Spanish, while #investigacion points to the increasing prominence of research as a collective demand within the community. Similarly, #discapacidad shows a clear upward trend, gaining relevance, and the growth of #pacientes suggests a gradual shift towards more explicitly patient-centered narratives, emphasizing lived experience and advocacy by those affected by rare diseases.

The data also reveal hashtags that have experienced a significant decline in relevance within the co-occurrence network during the study period (Table 7). Among these, #somosfeder shows the steepest statistically significant negative slope. This suggests that, while once central, the visibility of this organizational marker has diminished over time. Likewise, #hazlasvisibles also displays a marked and statistically significant decline. This hashtag, strongly linked to the visibility of rare diseases, emerged prominently in 2015 but has gradually been replaced by others over the years.

Other hashtags, such as #diadeandalucia or those tied to specific pathologies (#cushing, #acromegalia, #mastocitosis, #sindromedetourette), show moderate yet statistically significant decreases. Their decline may signal the waning influence of geographically or pathology-specific terms within the broader rare disease conversation, as the campaign consolidates around a more cohesive set of unifying hashtags.

6.2. Communities of Hashtags over Time

To investigate the presence of thematic communities within the hashtag co-occurrence network, we applied the Louvain clustering algorithm. Since the dataset was collected through queries including the main campaign hashtag (#diamundialdelasenfermedadesraras), this term appeared in almost all relationships within the co-occurrence networks of each campaign, making community detection difficult. For this reason, the main hashtag was removed from all networks, and communities were calculated based on the relationships among the remaining hashtags for each year. This strategy improved the modularity of the networks, raising values from around 0.3 in the original networks to approximately 0.6 after excluding the main hashtag.

Table 8. Total network metrics over the years.

Year	Nodes	Edges	Density	Communities	Modularity
2023	2247	7011	0.003	230	0.662
2022	2268	6589	0.003	210	0.609
2021	2631	8667	0.003	223	0.594
2020	2136	6532	0.003	186	0.621
2019	2573	8104	0.002	228	0.62
2018	2107	6146	0.003	201	0.649
2017	1106	1980	0.003	136	0.689
2016	629	937	0.005	103	0.63
2015	663	1053	0.005	127	0.399

presents the results of the clustering algorithm for each campaign. The total number of nodes and edges increased considerably between 2015 and 2018, remaining relatively stable from that point until 2023. A similar pattern is observed in the number of communities detected, which stabilized at around 200 from 2018 onwards.

Table 9. Metrics for the top 4 communities detected.

Year	Community 1		Community 2		Community 3		Community 4
	N. Hashtags (% of Total)	Density	N. Hashtags (% of Total)	Density	N. Hashtags (% of Total)	Density	N. Hashtags (% of Total)	Density
2023	673 (29.95)	0.009	184 (8.19)	0.023	96 (4.27)	0.041	113 (5.03)	0.083
2022	512 (22.57)	0.009	240 (10.58)	0.023	100 (4.41)	0.048	94 (4.14)	0.043
2021	777 (29.53)	0.007	150 (5.7)	0.032	135 (5.13)	0.055	139 (5.28)	0.061
2020	484 (22.6)	0.009	120 (5.62)	0.039	105 (4.92)	0.049	223 (10.44)	0.035
2019	433 (16.83)	0.011	147 (5.71)	0.031	186 (7.23)	0.027	200 (7.77)	0.031
2018	642 (30.47)	0.008	207 (9.82)	0.042	140 (6.64)	0.043	77 (3.65)	0.047
2017	170 (15.37)	0.021	80 (7.23)	0.037	99 (8.95)	0.033	77 (6.96)	0.036
2016	161 (25.6)	0.018	43 (6.84)	0.064	33 (5.25)	0.062	23 (3.66)	0.119
2015	190 (28.66)	0.018	30 (4.52)	0.094	21 (3.17)	0.11	36 (5.43)	0.081

reports some metrics for each of the four communities that include the most relevant hashtags of each campaign, while

Table 10. Most relevant hashtags in each of the top 4 communities detected.

Year	Hashtags Community 1	Hashtags Community 2	Hashtags Community 3	Hashtags Community 4
2023	#enfermedadesraras #investigacion #salud #rarediseaseday2023 #diagnostico #somosfeder #tiempoafavor #raredisease	#28defebrero #efemerides #felizmartes #buenosdias #apoyo #infancia #felizmartesatodos #pr	#enfermedadrara #sanidadpublica #masinvestigacion #vonhippellindau #enfermedadpocofrecuente #saf #masinversion #cancerpocofrecuente	#enfermedades #febrero #enfermedad #conciencia #febrero2023 #dia #raras #sabiasque
2022	#enfermedadesraras #investigacion #rarediseaseday2022 #visibilidad #feder #tratamientos #diagnostico #tratamiento	#28defebrero #raredisease #febrero #felizlunes #buenosdias #mwc22 #secret28f #mwc2022	#enfermedades #pacientes #pocofrecuentes #cambiominombre #raras #diagnosticos #apoyo #educacion	#salud #mexico #medicos #sosenfermedadesraras #visibles #rareismany #rareisproud #rareisstrong
2021	#enfermedadesrara #28defebrero #rarediseaseday2021 #salud #febreroraro #covid19 #raredisease #pacientes	#investigacion #visibilidad #diagnostico #tratamiento #ciencia #tratamientos #empatia #apoyo	#hipertensionpulmonar #somosfuertes #somoshiper #hiperunete #portodas #somosmuchos #rareisstrong #educacion	#felizdomingo #buenosdias #andalucia #escritodeldia #escritora #farmaceuticas #saludpublica #sigueleyendo
2020	#enfermedadesraras #29defebrero #feder #er #pacientes #ffpaciente #genetica #rarasnoinvisibles	#investigacion #visibilidad #apoyo #diagnostico #tratamiento #informacion #familias #derechos	#salud #febreroraro #medicina #genes #genoma #odisea #saludmental #retos	#felizsabado #coronavirus #cdmx #felizsabadoatodos #sabadodeganarseguidores #venezuela #felizfindesemana #felizviernes
2019	#enfermedadesraras #showyourrare #somosfeder #febreroraro #soyraro #ffpaciente #raredisease #pacientesquecuentan	#28defebrero #febrero #corresolidaris #josocsolidari #hacernosvisibles #high5forrarediseases #terapias #cornella	#investigacion #visibilidad #pocofrecuentes #rarasperonoinvisibles #inclusion #desafioduchenne #diversidad #inversion	#felizjueves #diadeandalucia #enfermeria #ciencia #sanidad #buenosdias #27defebrero #cientificas
2018	#enfermedadesraras #28defebrero #investigacion #salud #showyourrare #somosfeder #rarediseaseday2018 #hazlasvisibles	#felizmiercoles #diadeandalucia #felizdiadeandalucia #hoy #nieve #buenmiercoles #mwc18 #salamanca	#rarasnoinvisibles #solidario #ortopedia #aerscyl #granvia51 #ortopediasumesal #sumesal #empatia	#enfermedadrara #sabiasque #fibrosisquistica #ainhoa #acromegalia #neuromielitisoptica #d #hemofilia
2017	#enfermedadesraras #venezuela #hap #argentina #espana #aliber2017 #hp #raras	#investigacion #apoyo #feder #diamundi #worldraredisease #andalucia #lupus #sanidadpublica	#28defebrero #salud #rarasnoinvisibles #confuerzaganamostodos #medicina #ciencia #concienciacion #familia	#somosfeder #2 #diamundialenfermed #red #peronoinvisibles #r #ansedh #ehlersdanlos
2016	#enfermedadesraras #somosfeder #salud #creandoredesdeesperanza #hazlasvisibles #sanidad #felizlunes #todossomosraros	#29defebrero #infografia #skt #rarosnoinvisibles #colabora #fadepof #undiacomohoy #tal	#cedominombre #solidaridad #diamundi #diadelasenfermedadesra #diamundia #miasteniagravis #niemannpick #hoy	#investigacion #apoyo #esperanza #fuerza #linfedema #fb #fondos #inversion
2015	#hazlasvisibles #enfermedadesraras #28defebrero #raroesignorar #rarediseaseday2015 #fb #algorarosemueve #25	#enfermedades #raras #hazlasvisibleseci #dia #lovexair #rt #pontelarayaverde #video	#salud #venezuela #sanidad #granada #28f15 #ceuta #health #fabry	#investigacion #diagnostico #tratamientoya #cura #oi #stopame #tratamientos #diadelasenfermedadesr

shows the most relevant hashtags for each of these communities. Based on these results, several observations can be made.

A main community consistently accounts for between 20% and 30% of all hashtags used in each campaign, approximately double the size of the second-largest community in every case. This main community always contains the most relevant hashtag of each campaign, which—except in 2015—is #enfermedadesraras.

Communities headed by the date-specific campaign hashtags (#28defebrero, #29defebrero) can also be observed, although they show no clear semantic association with other hashtags in the same group. It is also common to find a community centered on greetings or using positive expressions (e.g., #buenosdias, #felizlunes, #felizmartes).

The role of #investigacion is particularly noteworthy. In six of the nine campaigns analyzed, this hashtag leads communities that include other terms related to the demands of people with rare diseases and their families. In the remaining three campaigns, it appears within the main community, ranking second or third in relevance.

Several communities dominated by disease-specific hashtags were also identified. While these communities are usually neither large nor composed of the most relevant campaign hashtags, in some cases—such as the community headed by #hipertensionpulmonar in 2021—they achieved a prominent position among the most notable communities.

To supplement the analysis in Section 5 regarding the #sanchezmentiroso hashtag, it should be noted that while it belongs to the main 2021 community, its low internal ranking (686th out of 777) confirms its peripheral structural position.

6.3. Hashtag Associations over Time

Association rule mining is a technique used to discover frequent relationships or co-occurrence patterns among hashtags employed in the conversation. This method was applied to the full dataset in order to identify which hashtags tended to appear together in the same tweets with significant frequency during each campaign period.

For this purpose, the Apriori algorithm, as implemented in the mlxtend.frequent_patterns Python module was employed to extract frequent itemsets and generate association rules based on support, confidence, and lift metrics. A minimum support threshold of 0.015 was selected to ensure that the rules captured associations beyond those expected with the main campaign hashtag. The results are presented in

Table 11. Hashtag association rules over the years.

Year	Antecedent	Consequent	Support	Confidence	Lift
2023	{‘#enfermedadrara’} {‘#investigacion’} {‘#enfermedadesraras’, ‘#28defebrero’} {‘#rarediseaseday2023’} {‘#enfermedadesraras’} {‘#somosfeder’} {‘#28defebrero’} {‘#tiempoafavor’}	{‘#diamundialdelasenfermedadesraras’}	0.016–0.042	0.73–0.94	0.93–1.2
	{‘#tiempoafavor’} {‘#somosfeder’}	{‘#enfermedadesraras’}	0.017	0.74–0.79	2.63–2.8
2022	{‘#nitanraras’} {‘#investigacion’} {‘#rarediseaseday2022’} {‘#compartetuscolores’} {‘#enfermedadesraras’} {‘#28defebrero’}	{‘#diamundialdelasenfermedadesraras’}	0.016–0.23	0.76–0.99	0.93–1.21
2021	{‘#sintomasdeesperanza’} {‘#somosfeder’} {‘#covid19’} {‘#enfermedadesraras’, ‘#rarediseaseday2021’} {‘#rarediseaseday2021’} {‘#investigacion’} {‘#enfermedadesraras’} {‘#28defebrero’}	{‘#diamundialdelasenfermedadesraras’}	0.018–0.20	0.82–0.98	0.96–1.15
2020	{‘#fasga’} {‘#fasga’, ‘#somosfeder’}	{‘#fasgasocialconlaser’}	0.019	1	37.15
	{‘#fasga’}	{‘#fasgasocialconlaser’, ‘#somosfeder’}	0.019	1	37.15
	{‘#fasga’} {‘#fasgasocialconlaser’} {‘#fasgasocialconlaser’, ‘#fasga’}	{‘#somosfeder’}	0.052	1	19.13
	{‘#febreroraro2020’} {‘#enfermedadrara’} {‘#rarediseaseday2020’} {‘#enfermedadesraras’} {‘#investigacion’} {‘#29defebrero’}	{‘#diamundialdelasenfermedadesraras’}	0.016–0.054	0.76–0.97	0.95–1.23
2019	{‘#enfermedadesraras’, ‘#juntossomosmas’} {‘#diamundialdelasenfermedadesraras’, ‘#juntossomosmas’} {‘#juntossomosmas’}	{‘#somosfeder’}	0.05–0.14	0.9–0.99	4.84–5.33
	{‘#febreroraro’} {‘#felizjueves’} {‘#enfermedadesraras’, ‘#showyourrare’} {‘#showyourrare’} {‘#investigacion’} {‘#28defebrero’}	{‘#diamundialdelasenfermedadesraras’}	0.016–0.033	0.83–0.99	1.07–5.33
	{‘#enfermedadesraras’, ‘#somosfeder’} {‘#somosfeder’} {‘#diamundialdelasenfermedadesraras’, ‘#somosfeder’}	{‘#juntossomosmas’}	0.048–0.14	0.6–0.85	3.72–5.27
	{‘#juntossomosmas’, ‘#somosfeder’} {‘#somosfeder’} {‘#juntossomosmas’}	{‘#enfermedadesraras’}	0.1–0.12	0.62–0.68	2.27–2.5
2018	{‘#nieve’} {‘#felizdiadeandalucia’, ‘#nieve’} {‘#felizdiadeandalucia’} {‘#hazlasvisibles’} {‘#felizmiercoles’} {‘#investigacion’} {‘#28defebrero’} {‘#showyourrare’} {‘#enfermedadesraras’} {‘#salud’}	{‘#diamundialdelasenfermedadesraras’}	0.018–0.14	0.7–1	0.92–1.17
	{‘#nieve’}	{‘#felizdiadeandalucia’, ‘#diamundialdelasenfermedadesraras’}	0.018	0.94	34.2
	{‘#nieve’} {‘#nieve’, ‘#diamundialdelasenfermedadesraras’}	{‘#felizdiadeandalucia’}	0.018	0.94	33.8
2017	{‘#felizmartes’} {‘#unasonrisapocofrecuente’} {‘#investigacion’} {‘#28defebrero’} {‘#enfermedadesraras’}	{‘#diamundialdelasenfermedadesraras’}	0.019–0.067	0.61–0.97	0.82–1.13
2016	{‘#29defebrero’} {‘#cedominombre’}	{‘#diamundialdelasenfermedadesraras’}	0.04–0.069	0.59–0.63	0.92–0.97
2015	{‘#somosvisibles’} {‘#28defebrero’}	{‘#diamundialdelasenfermedadesraras’}	0.02–0.022	0.64–0.99	1.24–1.95

, which reports the rules obtained across different years, restricted to those with confidence values greater than 0.6 and lift values equal to or above 0.9.

Overall, the findings reveal a core set of strongly interrelated hashtags that remain consistently present across all years. At the same time, the analysis highlights variations that reflect the thematic emphases of specific campaigns.

The main campaign hashtag, #DiaMundialDeLasEnfermedadesRaras, appears in the vast majority of tweets, serving as the anchor of the conversation. Since 2017, the hashtag #enfermedadesraras has been systematically associated with the campaign hashtag, reflecting a deliberate strategy to connect the specific event with the broader awareness discourse on rare diseases. Another prominent element is #investigacion (“research”), which shows a particularly strong association with the campaign hashtag in 2017, the year when the official theme was “Research is our hope.” Since then, this hashtag has remained significantly linked to Rare Disease Day in subsequent campaigns.

The temporal hashtag #28deFebrero, marking the date of the event, also emerges as a recurrently associated term, reinforcing the community’s identification with the chosen celebration day. From 2020 onwards, the English hashtag #RareDiseaseDayYYYY appears in the association rules, suggesting a gradual shift toward greater internationalization of the campaign. Before this period, #showyourrare had been the only English-language term consistently present in relevant associations.

Occasionally, unrelated hashtags such as #nieve (“snow”) or #felizdiadeandalucia (“Happy Andalusia Day”) appear within the association rules, reflecting the influence of external circumstances such as seasonal events or regional celebrations on the online conversation. Campaign-specific hashtags, promoted by particular, influential accounts, also emerge as relevant due to their wide diffusion in connection with Rare Disease Day.

It is particularly noteworthy that the 2021 edition incorporated #covid19 into the set of significantly associated hashtags, reflecting an effort to connect the challenges of rare diseases with the broader context of the global pandemic.

7. Discussion

Analysis of the hashtags used on Twitter during Rare Disease Day between 2008 and 2023 reveals a significant evolution in the volume, reach, and nature of participation. In the early years, conversation on Twitter was in its infancy, in line with the platform’s lower penetration; however, over time, there has been a sharp increase in both the number of tweets and the diversity of hashtags used. This increase reflects how social media has become an important tool for raising awareness of rare diseases, a trend consistent with other areas of digital health. Several studies have highlighted that hashtags facilitate access to health information and increase its visibility by grouping content and communities around health topics [28].

The main findings of the analysis indicate that participation on Twitter during Rare Disease Day has not only grown in volume, but also in the plurality of voices and messages. Initially, posts were mostly institutional or conveyed basic information, while in subsequent years, there has been a greater presence of patients, family members, and citizens articulating their own slogans. For example, in 2014, generic hashtags emerged focusing on the demands of the rare disease community—such as #education, #research, #visibility, and #care—which referred to the fundamental needs of this group. It is noteworthy that #investigacion (#research), alluding to the demand for more research into rare diseases, remained consistently among the most widely used hashtags in subsequent years, even above some official campaign tags. The longitudinal analysis confirms this pattern: hashtags such as #investigacion and #pacientes have shown statistically significant upward trajectories in structural relevance, reinforcing the idea that research and patient-centered narratives are gaining prominence over time.

This suggests that the community’s priorities (among which greater scientific investment seems to be the main one) found a permanent space on Twitter, transcending the specific campaign of each year. This phenomenon coincides with the findings of [10], who argue that empowered patients can “solve the zebra puzzle”—a metaphor for rare diseases—through social media, driving research and visibility from the grassroots level [10]. In line with the theory of connective action in health [39], social media allows for flexible mobilization focused on personal narratives rather than hierarchical structures, something that is clearly reflected in the proliferation of organic slogans around Rare Disease Day. The fact that “research” remains the dominant and structural theme after many years of activism underscores the collective perception that scientific progress, despite advances, remains insufficient. The hashtag, therefore, serves as a powerful annual and public reminder of this structural gap between patient needs and the response of the scientific and healthcare system.

The evolution of the most widely used hashtags is one of the most revealing findings of the study. There is a clear transition from generic and descriptive terms such as #health or #diseases in the early years to specific, evocative, and, crucially, actionable campaign slogans such as #HazlasVisibles (in year 2015), #CedoMiNombre (in year 2016), and #ShareYourColors (in year 2022). This trajectory illustrates how the community learned to use hashtags not only as metadata tags to organize content, but as tools for mobilization.

Hashtags serve multiple communicative functions: they mark a topic, aggregate disparate conversations, encourage socialization, express attitudes, and promote social movements. Analysis shows that the rare disease community has strategically deployed hashtags to increase the visibility of its cause, organize the flow of information around an annual event, and develop brand recognition for its campaigns. The success of hashtags such as #HazlasVisibles lies in their call to action, a highly effective tactic in social media advocacy that invites the audience to move from being passive spectators to active participants. Beyond its technical function on the social platform, a hashtag is an artifact of collective identity. The choice and popularity of certain hashtags over time show how the community perceives itself and how it wants to be perceived by the rest of society. In this regard, the association rule mining results indicate that some terms consistently appear together, such as #diamundialdelasenfermedadesraras with #enfermedadesraras and #investigacion, reflecting a deliberate discursive alignment between the global campaign, the general framing of rare diseases, and the structural demand for more research.

The analysis shows that the hashtag system used started from a vague initial situation and evolved into a structured system based on different types of tags:

• Official campaign hashtags: Promoted by some of the central organizations (e.g., EURORDIS, FEDER) to unify the annual message (e.g., #TiempoAFavor). These institutional hashtags act as catalysts, generating peaks of concentrated participation around awareness days [28]. Various studies show how public health agencies manage to increase the reach of messages by coordinating campaigns with specific hashtags [18,28].
• Community hashtags (grassroots): These arise organically from patients and their families, healthcare professionals, or agencies aware of the cause. These hashtags usually represent a fundamental demand. An example of this type of hashtag is #RarasNoInvisibles, which remained relevant over time as a slogan for the rare disease movement, emphasizing the need to not leave those living with these conditions invisible. It is a clear example of how a civil society initiative can be integrated into the official narrative: #RarasNoInvisibles complemented and reinforced the message of #HazlasVisibles, both aiming for visibility as a goal, but from different origins (community vs. institutional).
• Persistent Thematic Hashtags: Terms that transcend annual campaigns and represent the pillars of the conversation, being related to the needs of patients and families (e.g., #research, #diagnosis).

The literature reports similar cases in digital health where grassroots efforts and official campaigns converge on common goals. For example, in the analysis of World Breastfeeding Week [40], Twitter communities were identified that were made up of both individual users and professional organizations, all promoting the cause from different angles. This convergence of diverse actors through hashtags illustrates the horizontal and collaborative nature of social media as a space for health activism [41]. Other studies on health campaigns on Twitter have observed that users often incorporate additional hashtags to the official ones to enrich the message and connect with multiple communities [28], finding that in the Heart Month campaign, alongside the official tags (#AmericanHeartMonth, etc.), users introduced hashtags such as #HeartHealth or #WearRedDay, broadening the reach to specific related topics. At the same time, organic hashtags such as #investigación or those related to visibility coexisted with the official ones, indicating recurring topics of interest (scientific research, media visibility) that people wanted to highlight constantly. This is corroborated by the clustering analysis, which shows that the campaign progressively consolidated into stable thematic communities: one large community consistently accounting for 20–30% of hashtags, led by #enfermedadesraras, and smaller communities structured around research, patient demands, or specific pathologies. The persistence of a research-centered cluster—led by #investigacion in most campaigns—highlights its structural role as a unifying theme across the years.

The consistent presence of some terms suggests that the rare disease community uses Twitter not only to support the annual campaign but to continuously advocate for their needs. In fact, Twitter’s ability to foster permanent communities around health conditions is well documented; for example, communities with permanent hashtags have been created for different health conditions that maintain dialogue even outside of campaign days, as in the case of brain tumors with the hashtag #BTSM [42], breast cancer with the hashtag #BCSM [43] or type I diabetes with the hashtags #WeAreNotWaiting and #OpenAPS [44].

An interesting finding is the participation of private and healthcare sector actors in hashtag conversations. For example, in 2022, the pharmaceutical company Sanofi promoted the hashtag #MeetTheUnmet as part of its “Raras pero Reales” (“Rare but Real”) campaign (from the @RarasReales account), which achieved widespread coverage, especially in Spain. Similarly, hospitals and research centers have used Twitter to promote events related to the global day: in 2023, CIBERER (the Spanish Network of Biomedical Research Centers in Rare Diseases) managed to position its hashtag #InvestigarEsAvanzar (#ResearchIsProgress) among the most widely used, linked to a scientific conference of the same name. This reinforces the idea that the conversation ecosystem includes not only those affected and Non-Governmental Organizations, but also health professionals, researchers, and committed companies, all contributing their initiatives.

The emergence of hashtags with an explicit political slant, such as #sanchezmentiroso (2021) or hashtags related to Cuba and Venezuela in 2023 (#CubaPorLaVida, #ChávezInmortal), introduces another layer of complexity. It is crucial to differentiate between genuine political activism and “astroturfing,” a deceptive practice in which orchestrated and funded campaigns masquerade as spontaneous grassroots support.

The hashtag #sanchezmentiroso, created by a patient to denounce alleged government inaction, appears to be a case of genuine protest speech. Its virality was likely driven by strong negative emotions (anger, frustration), which, as research has shown, are powerful drivers of participation and dissemination on social media [45,46]. On the other hand, hashtags such as #ChávezInmortal or #CubaPorLaVida could be considered suspicious of being astroturfing tactics [47]. Although their content is not thematically distant from rare diseases, their sudden appearance and coordinated dissemination by a specific group of accounts suggest an attempt to take advantage of the event’s visibility to promote a foreign political agenda. Social network analysis (SNA) reinforces this hypothesis by showing that these hashtags, despite their volume, are structurally peripheral (they can be seen in Figure 4, repelled towards the periphery of the graph) and do not integrate into the central conversation of the community. In the case of the hashtag #ChávezInmortal, the account that created the original tweet did so automatically, probably taking the text from a news aggregator, including mentions to different accounts in the tweet to gain traction. It so happens that the vast majority of the accounts mentioned are currently suspended on the platform. In the case of hashtags related to Cuba, this type of action has been observed previously, as in the case of the COVID-19 pandemic, where the predominant interactions on Twitter during the period analyzed were polarized toward ideologies in favor of the Cuban government’s policies in this health crisis [48]. Understanding these power dynamics is essential to assessing the impact and communicative effectiveness of any campaign.

The emergence of #coronavirus and #covid19 as relevant hashtags in the analysis of 2020 and 2021 illustrates how the Rare Disease Day conversation intersected with a broader global social trend. Qualitative analysis of the tweets shows that users did not primarily discuss virological or epidemiological aspects of the new virus, but rather emphasized its social and systemic implications for people with rare diseases, such as the disruption of health and social services, the fear of being overlooked in the midst of the new emergency, and comparisons between the substantial investment in COVID-19 and the chronic scarcity of resources for rare conditions. The issues identified reflect documented concerns about the disproportionate impact of the pandemic on patients with chronic and rare diseases [49,50,51,52]. While these narratives provide insight into the perceptions and concerns expressed by the community, they should not be interpreted as objective indicators of system vulnerability, which would require complementary evidence such as epidemiological or health outcome data.

Another significant finding of this study comes from the comparison between frequency metrics (number of original tweets and retweets along with the hashtags used in them) and structural centrality metrics derived from social network analysis (SNA), specifically eigenvector centrality. This comparison reveals a crucial distinction between popularity and structural relevance. Hashtags that achieved widespread dissemination in a given year, such as #sanchezmentiroso (2021), #PasaPalabra20Aniversario (2021), or the political hashtags of 2023, dominated the retweet lists but disappeared completely from the lists of structurally most important hashtags generated by SNA. In contrast, hashtags such as #FEDER or #diagnostico, with a more modest volume of use and dissemination, emerge as relevant nodes in the network structure over several years. This difference demonstrates the limitation of volume metrics and the power of SNA to uncover the underlying architecture of the conversation, as seen in previous work [28,53]. The integration of trend analysis further clarifies these differences: hashtags with high short-term popularity often show flat or declining slopes in longitudinal centrality (e.g., campaign-specific or regional tags), while structural hashtags related to core demands (#investigacion, #pacientes, #discapacidad) exhibit sustained upward trajectories. This strengthens the argument that structural analysis provides a deeper understanding of the long-term dynamics of advocacy.

Hashtags have enabled collective action to be synchronized: knowing which tag to use, organizations, professionals, affected parties, and individuals coordinate to tweet on the days around 28/29 February, ensuring that the issue gains media attention. This synergistic effect is consistent with theoretical models of public health communication that postulate that exposure to social media campaigns can amplify reach and even lead to cognitive or behavioral changes in the audience [54,55]. While transforming awareness into behavior is complex, social networks offer a space to reinforce health messages repeatedly and creatively, which is an important first step [56]. In the context of rare diseases, where raising awareness among the public and decision-makers is a central objective, the impact of campaigns on Twitter is often notable, as evidenced by the reports on the reach achieved in each Rare Disease Day campaign, available on the website https://www.rarediseaseday.org/ (accessed on 20 August 2025).

8. Limitations

While this study provides a comprehensive overview of the dynamics of hashtag use on Twitter on Rare Disease Day in Spanish over a 15-year period, it is important to acknowledge several limitations of the study:

• Platform bias: The analysis focuses exclusively on Twitter. While it is a crucial platform for public discourse, conversations on other social media platforms, such as Facebook, Instagram, TikTok, or specialized patient forums, may present substantially different dynamics, actors, and topics. The growing difficulty of accessing data from these platforms (including the current X) for large-scale research represents a significant obstacle to this type of study.
• Data query mechanism: The choice of a number of specific character strings and search terms for capturing the data means that some messages (tweets) may not have been captured, but could be relevant to the analysis of the conversation.
• This study assumes hashtags as central mechanisms for structuring and amplifying conversations on Twitter/X. However, the communicative ecosystem of the platform has evolved significantly in recent years. Hashtags have lost much of their former strength as a mandatory component for visibility, since content discovery is now also driven by algorithms and recommendation systems. While hashtags remain valuable when used strategically and selectively, their declining centrality in shaping online discourse should be acknowledged. Consequently, the long-term trends identified in this study must be interpreted with caution, as future campaigns may rely less on hashtags and more on alternative mechanisms of engagement and dissemination.
• Linguistic and cultural limitations: The study is restricted to the Spanish language. A cross-cultural comparative analysis of the campaign hashtags could reveal important differences in priorities, communication styles, and cultural frameworks between different regions of the world.
• Depth of content analysis: The present analysis is based on the frequency and co-occurrence of hashtags, which act as a proxy for conversation topics. However, it does not analyze the full content of tweets or multimedia content (images, videos, infographics), which are increasingly important components of digital communication. A sentiment analysis or deeper topic modeling of the text could reveal emotional and narrative nuances that hashtags alone cannot capture.
• Real-world impact of the online campaign: This is an observational and longitudinal study. It can identify patterns and trends in digital conversation, but it cannot establish a direct causal relationship between hashtag campaigns and changes in behavior, public awareness, or political decisions in the real world.

9. Conclusions

This study has conducted the first longitudinal analysis of Spanish-language conversation on Twitter around Rare Disease Day, tracing its evolution over 16 years, from its inception in 2008 to its consolidation in 2023. The results not only quantify the growth of an awareness event but also allow us to observe the maturation of a cohesive digital health movement with well-defined strategies.

The trajectory of the dominant hashtags shows a collective learning process from a hesitant start to the creation and adoption of specific, evocative campaign slogans that include calls to action and a sense of community. While annual campaign slogans changed, the hashtag #investigación (#research) remained the most persistent and structurally central theme for over a decade. Its constant prominence, validated by both frequency and centrality metrics in the network, as well as its leading role in thematic clusters across the years, indicates not only persistence but also integrative capacity in structuring the discourse, establishing it as the fundamental and non-negotiable demand of the community.

The conversation is not a monologue, but a dynamic environment of narrative negotiation. Analysis reveals an ecosystem with differentiated roles: patient organizations such as FEDER act as central architects that hold the network together; grassroots activism brings authenticity and emotional solidarity; some professionals or affected individuals emerge as highly relevant actors over several years, and external actors such as celebrities or the media generate peaks of visibility through the “messenger effect,” although often with limited structural integration into the community dialogue. Likewise, the vulnerability of the conversation to being instrumentalized by foreign political agendas is evident, underscoring the need to care for and preserve these spaces for debate on such complex and sensitive health issues.

Despite the enthusiasm generated and the widespread participation in various campaigns to promote and raise awareness of different health-related issues, the academic literature debates the ultimate effectiveness of such campaigns on online social media in bringing about tangible changes in health behaviors or policies. There is still limited evidence of behavior changes attributable to health campaigns on Twitter, partly because many evaluations focus on dissemination metrics rather than concrete results. Although this study was not aimed at verifying the specific impact of the various campaign initiatives, it found, thanks to its longitudinal nature, that year after year a significant cohesive virtual community has formed around the issue of rare diseases in Spanish language, with a set of hashtags that has matured over time to form a cohesive core that reflects the main concerns and demands of this community. For this reason, social and health services and those responsible for health policies in each country should be aware of and participate in this type of campaign, offering at least some kind of feedback that lets this community feel that someone is listening to them.

Future lines of research include conducting an analysis of the main actors involved in the different Rare Disease Day campaigns to better understand the dynamics of the creation and dissemination of hashtags and narratives. The study has also served to identify different topics that would be interesting to explore further through techniques of content analysis using quantitative and qualitative methods in order to better understand the debate surrounding them.