1. Introduction
As of writing this report, the United States Centers for Disease Control and Prevention (CDC) has recommended the use of three Coronavirus disease 2019 (COVID-19) vaccines, with more in development [
1]. Vaccination campaigns for COVID-19 will be key in curbing this global pandemic, but must be purposeful to ensure they do not propagate existing disparities of COVID-19′s impact on communities of color. COVID-19 has been particularly devastating to Black and Latino/Hispanic (henceforth: Latinx) communities in the U.S. [
2,
3]. Long-standing social inequities in social determinants of health place communities of color at elevated risk of COVID-19 infection, severe illness, and death compared to non-Hispanic whites [
4]. Therefore, it is imperative to document and strategize how COVID-19 vaccines can be successfully disseminated throughout these communities.
Previous research shows that Latinx adults are less likely than non-Hispanic whites to be vaccinated [
5,
6]. Low perceived risk of influenza and healthcare providers’ failure to recommend vaccination may contribute to lower vaccination rates [
7]. Compared to non-Hispanic whites, U.S. Latinxs reported more vaccine-related side effects and were more likely to be misinformed about the availability of vaccines [
8]. In addition to individual-level barriers, systemic barriers have been well documented. Latinxs in the U.S. are less likely to have access to health care and more likely to suffer the effects of discriminatory policies, higher healthcare costs, lack of insurance, and language barriers; all of these factors constitute significant challenges to equitable public health efforts [
3].
Data on the acceptability of the COVID-19 vaccines among minority populations are limited. However, a cross-sectional survey of a representative sample of U.S. adults found that both Black and Latinx respondents reported lower intent to be vaccinated for COVID-19 compared to non-Hispanic whites [
9]. Another nationally representative longitudinal study found that intent to receive vaccination declined between April and December of 2020, with the highest decline observed among U.S. Hispanics [
10]. This is consistent with previous findings from the 2009 H1N1 pandemic, which observed that intent to receive vaccination may be highest early in a pandemic before a vaccine is available [
11].
With respect to the impact of COVID-19 in Puerto Rico (PR), it is important to highlight the unique socio-political status of PR as a U.S. territory, the economic crisis in 2016, and the devastating force of Hurricanes Irma and Maria in 2017 [
12]. Because of these variables, and their ongoing impact in PR, it has been difficult to measure the impact of COVID-19 in PR as well as the overall effectiveness of current vaccination efforts. Current analyses suggest that the number of COVID-19 associated deaths in PR during the pandemic is higher than expected, with the number of COVID-19-associated deaths rising to more than double the numbers originally reported [
13]. With the introduction of the SARS-CoV vaccines, it is important to determine variables associated with intent to receive vaccination. Unfortunately, there are no studies to date that have documented intent to receive vaccination in PR against COVID-19. In this Short Communication, we report the factors associated with the intent to receive vaccination against COVID-19 among adults living in Puerto Rico.
2. Materials and Methods
We conducted an online survey among adults 21 years of age and older living in Puerto Rico to identify social and behavioral factors impacted by the COVID-19 pandemic (21 is the age of majority in Puerto Rico). The data collection instrument was available in Spanish (Puerto Rico’s official language) in a secured online platform. The data collection instrument included several measures to assess socio-demographics, respondents’ experiences with COVID-19 information sources, perceived impact of COVID-19, and perceived governmental response, and were culturally adapted following a process previously used by the research team [
14,
15] and integrated previously validated measures [
16]. The final survey instrument contained 70 items in total, and skip patterns were included to reduce burden among participants. Intention to get vaccinated against COVID-19 was assessed asking, “If there existed an approved vaccine to prevent the coronavirus infection, how likely is it that you would get vaccinated?” followed by a 4-point scale (not at all likely to very likely). Respondents were recruited using social media platforms and with the support of several community-based organizations that sent blast emails and posted study information on their websites and social media from 7 July 2020 to 13 July 2020. After screening and providing consent to participate, a total of
n = 1031 respondents completed the survey. All research procedures were approved by the Human Research Subjects Protection Office of HIDDEN FOR PEER REVIEW.
Of the 1031 participants who completed the survey, two participants were excluded for incomplete data, leaving 1029 survey responses in the dataset. A total of 1016 responses were available for analysis from respondents who reported their intention to get vaccinated for COVID-19. The intent to receive vaccination was then dichotomized to maximize the number of participants in each category. Risk factor count was calculated as the number of the following factors: diagnosed with heart disease, respiratory illness, cerebral illness, diabetes, kidney disease, cancer, or age ≥ 65 years old. Health regions were derived from self-reported postcodes. All measured variables were selected a priori to be analyzed independently for association with intent to receive vaccination using Chi-square tests for categorical variables and t-tests for continuous variables. Variables with significant association and variables selected a priori (perception of government response and overall impact of COVID-19) were included in the multivariate logistic regression analysis. Adjusted odds ratios and their p-values for the independent variables were reported. The significance level of all analyses was at α = 0.05. All analysis was conducted with SAS 9.4 software.
3. Results
Respondents had a broad distribution of demographic and socioeconomic characteristics (
Table 1), with a mean age of 46 years old and 73% identifying as women. In the bivariate analysis, younger age, higher education, pre-COVID-19 employment, male sex, gay/bisexual identity, and single marital status were all associated with increased intention to be vaccinated. Increasing numbers of risk factors for poorer outcomes from COVID-19 (i.e., aged 65 and older, comorbidities) were not associated with vaccine intention.
No significant relationship was observed between pre-COVID-19 employment, sexual orientation, and marital status and intent to receive vaccination after adjustment (
Table 1). However, younger, male respondents, and those with higher educational attainment, reported higher intent to receive vaccination. Respondents who had a yearly income of
$50,000 or more had significantly higher intent to receive vaccination (POR = 2.4,
p = 0.0096) than those who earned less than
$10,000. Respondents living outside of the San Juan metro region had significantly lower intent to receive vaccination when compared to respondents who lived in the metro region (POR = 0.647,
p = 0.0082). Respondents who were less likely to get vaccinated expressed less worry about the impact of COVID-19 and perceived the Puerto Rican government’s response to be deficient.
Respondents who reported a high degree of confidence in one’s ability to evaluate the credibility of information about COVID-19 reported higher intent to receive vaccination (
Table 2). National and international health organizations (World Health Organization, Centers for Disease Control and Prevention) were identified as the most reliable sources for COVID-19-related information for respondents with a high likelihood of getting vaccinated (75%), followed by healthcare professionals (70%) and news programs (51%). While these sources were also selected as the most reliable among respondents with a low likelihood of vaccination, healthcare professionals and national/international health organizations were trusted at significantly lower rates than those intending to vaccinate (59% and 56%, respectively).
4. Discussion
These results, which are part of a larger survey created to evaluate the impact of COVID-19 on people living in Puerto Rico, provide insight into vaccine acceptability and intent to receive vaccination amongst the respondents and may be useful to current vaccination efforts in Puerto Rico and the U.S. Although the total number of risk factors for poor COVID-19 outcomes was not associated with intent to receive vaccination, decreased intention observed among older respondents is troubling.
Several limitations should be considered when interpreting the findings of this study. As mentioned previously, vaccine acceptability tends to decrease over time following the onset of a pandemic, and responses from July of 2020 may overestimate intent to receive vaccination. Moreover, the item assessing intent to receive vaccination was posed in a hypothetical manner as no vaccine was yet available. As such, perceptions and intentions may have changed since that time, in particular with regards to media coverage of different vaccine manufacturers and vaccines currently approved or in development. Further, the study used a convenient online sample of adults. This may have led to self-selected participants who had access to the internet and were interested in the topic. Despite these limitations, this was the best approach to capture information during the stay-at-home orders that were in place at the time of data collection. Lastly, it is possible that confounding factors not collected by the survey instrument such as religion or health literacy may have additional effects on intent to receive vaccination.
5. Conclusions
These findings highlight the importance of considering sociodemographic characteristics identified with low intent to receive vaccination when designing public messaging related to increasing COVID-19 vaccinations. In particular, older individuals earning less than $50,000 a year and those living in rural areas may be at particular risk of not being vaccinated. Furthermore, in light of reported perceptions of the government’s response to the COVID-19 crisis, communication initiatives should consider efforts to promote vaccinations via trusted sources of information, particularly among those who are less likely to get vaccinated. Communication campaigns may benefit from using established guidance from the CDC and WHO, and by being delivered by local healthcare professionals and through news outlets to ensure success.
Author Contributions
Conceptualization, K.M., J.P.Z., C.E.R.-D.; methodology, K.M., C.Z., S.M.M.-R., C.E.R.-D.; formal analysis, K.M., C.Z., J.P.Z., Y.M.R., K.F., E.S., S.M.M.-R., C.E.R.-D.; data curation, C.Z.; writing—original draft preparation, K.M., J.P.Z., K.F.; writing—review and editing, C.Z., Y.M.R., E.S., S.M.M.-R., C.E.R.-D.; visualization, C.Z. All authors have read and agreed to the published version of the manuscript.
Funding
The work of Juan Pablo Zapata was supported by the National Center for Advancing Translational Sciences, National Institutes of Health, through grant numbers UL1TR001436 and 1TL1TR001437. The research presented in this paper is that of the authors and does not reflect the official policy of the NIH.
Institutional Review Board Statement
The study was conducted according to the guidelines of the Declaration of Helsinki, and approved by the Institutional Review Board of the University of Puerto Rico Medical Sciences Campus (Protocol #: A9650220; approved 7 July 2020).
Informed Consent Statement
Written informed consent was waived due by the Institutional Review Board under Exemption 2: Research involving the use of survey procedures recorded in a manner in which human subjects are unable to be identified and in which any disclosure of the human subjects’ responses outside the research context could not reasonably place the subject at risk of criminal or civil liability or be damaging to the subjects’ financial standing, employability, or reputation.
Data Availability Statement
Data are available upon completion of a data sharing agreement with the principal investigator, Carlos E. Rodriguez-Diaz.
Acknowledgments
The researchers wish to thank the respondents who participated in this research.
Conflicts of Interest
The authors declare no conflict of interest.
References
- Centers for Disease Control and Prevention. Different COVID-19 Vaccines 2021. Available online: https://www.cdc.gov/coronavirus/2019-ncov/vaccines/different-vaccines.html (accessed on 7 June 2021).
- Millett, G.A.; Jones, A.T.; Benkeser, D.; Baral, S.; Mercer, L.; Beyrer, C.; Honermann, B.; Lankiewicz, E.; Mena, L.; Crowley, J.S.; et al. Assessing differential impacts of COVID-19 on black communities. Ann. Epidemiol. 2020, 47, 37–44. [Google Scholar] [CrossRef] [PubMed]
- Rodriguez-Diaz, C.E.; Guilamo-Ramos, V.; Mena, L.; Hall, E.; Honermann, B.; Crowley, J.S.; Baral, S.; Prado, G.J.; Marzan-Rodriguez, M.; Beyrer, C.; et al. Risk for COVID-19 infection and death among Latinos in the United States: Examining heterogeneity in transmission dynamics. Ann. Epidemiol. 2020, 52, 46–53. Available online: http://www.sciencedirect.com/science/article/pii/S1047279720302672 (accessed on 23 July 2020). [CrossRef] [PubMed]
- Laster Pirtle, W.N. Racial Capitalism: A Fundamental Cause of Novel Coronavirus (COVID-19) Pandemic Inequities in the United States. Health Educ. Behav. 2020, 47, 504–508. [Google Scholar] [CrossRef] [PubMed]
- Lu, P.-J.; Singleton, J.A.; Euler, G.L.; Williams, W.W.; Bridges, C.B. Seasonal influenza vaccination coverage among adult populations in the United States, 2005–2011. Am. J. Epidemiol. 2013, 178, 1478–1487. [Google Scholar] [CrossRef] [PubMed] [Green Version]
- FluVaxView Interactive! Centers for Disease Control and Prevention. 2021. Available online: https://www.cdc.gov/flu/fluvaxview/interactive-general-population.htm (accessed on 8 February 2021).
- Arriola, C.S.; Mercado-Crespo, M.C.; Rivera, B.; Serrano-Rodriguez, R.; Macklin, N.; Rivera, A.; Graitcer, S.; Lacen, M.; Bridges, C.B.; Kennedy, E.D. Reasons for low influenza vaccination coverage among adults in Puerto Rico, influenza season 2013–2014. Vaccine 2015, 33, 3829–3835. [Google Scholar] [CrossRef] [PubMed] [Green Version]
- Hebert, P.L.; Frick, K.D.; Kane, R.L.; McBean, A.M. The causes of racial and ethnic differences in influenza vaccination rates among elderly Medicare beneficiaries. Health Serv. Res. 2005, 40, 517–537. [Google Scholar] [CrossRef] [PubMed] [Green Version]
- Fisher, K.A.; Bloomstone, S.J.; Walder, J.; Crawford, S.; Fouayzi, H.; Mazor, K.M. Attitudes Toward a Potential SARS-CoV-2 Vaccine: A Survey of U.S. Adults. Ann. Intern. Med. 2020, 173, 964–973. [Google Scholar] [CrossRef] [PubMed]
- Szilagyi, P.G.; Thomas, K.; Shah, M.D.; Vizueta, N.; Cui, Y.; Vangala, S.; Kapteyn, A. National Trends in the US Public’s Likelihood of Getting a COVID-19 Vaccine—1 April to 8 December 2020. JAMA 2021, 325, 396–398. [Google Scholar] [CrossRef] [PubMed]
- Gidengil, C.A.; Parker, A.M.; Zikmund-Fisher, B.J. Trends in risk perceptions and vaccination intentions: A longitudinal study of the first year of the H1N1 pandemic. Am. J. Public Health 2012, 102, 672–679. [Google Scholar] [CrossRef] [PubMed]
- Gelpí-Acosta, C.; Rodríguez-Díaz, C.E.; Aponte-Meléndez, Y.; Abadie, R. Puerto Rican Syndemics: Opiates, Overdoses, HIV, and the Hepatitis C Virus in a Context of Ongoing Crises. Am. J. Public Health 2020, 110, 176–177. [Google Scholar] [CrossRef]
- Azofeifa, A.; Valencia, D.; Rodriguez, C.J.; Cruz, M.; Hayes, D.; Montañez-Báez, E.; Tejada-Vera, B.; Villafañe-Delgado, J.E.; Cabrera, J.J.; Valencia-Prado, M. Estimating and characterizing COVID-19 deaths, Puerto Rico, March–July 2020. Public Health Rep. 2021, 136, 354–360. [Google Scholar] [CrossRef] [PubMed]
- Rodríguez-Díaz, C.E.; Martínez-Vélez, J.J.; Jovet-Toledo, G.G.; Vélez-Vega, C.M.; Hernández-Otero, N.; Escotto-Morales, B.; Mulinelli-Rodríguez, J.J. Challenges for the Well-Being of and Health Equity for Lesbian, Gay, and Bisexual People in Puerto Rico. Int. J. Sex. Health 2016, 28, 286–295. [Google Scholar] [CrossRef]
- Rodríguez-Díaz, C.E.; Jovet-Toledo, G.G.; Vélez-Vega, C.M.; Ortiz-Sánchez, E.J.; Santiago-Rodríguez, E.I.; Vargas-Molina, R.L.; Rodríguez Madera, S.L.; Mulinelli-Rodríguez, J.J. Discrimination and Health among Lesbian, Gay, Bisexual and Trans People in Puerto Rico. Puerto Rico Health Sci. J. 2016, 35, 154–159. [Google Scholar]
- Harkness, A.; Behar-Zusman, V.; Safren, S.A. Understanding the Impact of COVID-19 on Latino Sexual Minority Men in a US HIV Hot Spot. AIDS Behav. 2020, 24, 2017–2023. [Google Scholar] [CrossRef] [PubMed]
Table 1.
Bivariate and Multivariate Analyses of Socio-Demographic Characteristics with Vaccine Acceptability.
Table 1.
Bivariate and Multivariate Analyses of Socio-Demographic Characteristics with Vaccine Acceptability.
Variable (N, %) | If There Existed an Approved Vaccine to Prevent the Coronavirus Infection, How Likely is It that You Would Get Vaccinated? | Multivariate Regression Analysis |
---|
High Likelihood | Low Likelihood | p-Value | AOR | p-Value |
---|
Total participants (N, %) | 704 (68.4%) | 312 (30.3%) | | | |
Age | n | 704 | 312 | | | |
Mean (SD) | 44.9 (15.8) | 50.1 (13.2) | <0.0001 | 0.98 | 0.0141 |
Age group | (n = 1016) | | <0.0001 | | |
21–29 | 180 (84.9%) | 32 (15.1%) | | | |
30–39 | 93 (73.8%) | 33 (26.2%) | | | |
40–49 | 121 (64.7%) | 66 (35.3%) | | | |
50–59 | 168 (63.4%) | 97 (36.6%) | | | |
60+ | 142 (62.8%) | 84 (37.2%) | | | |
Education | (n = 1013) | | 0.0013 | | |
High school or less | 35 (49.3%) | 36 (50.7%) | | (ref) | (ref) |
Some years of university | 161 (68.5%) | 74 (31.5%) | | 2.168 | 0.0121 |
Bachelor’s degree | 265 (70.3%) | 112 (29.7%) | | 1.839 | 0.044 |
Post-graduate | 241 (73.0%) | 89 (27.0%) | | 1.952 | 0.0349 |
Refuse to answer | 2 (66.7%) | 1 (33.3%) | | 3.12 | 0.3949 |
Employment before COVID-19 | (n = 1003) | | 0.0003 | | |
Full time job | 298 (71.5%) | 119 (28.5%) | | (ref) | (ref) |
Part time job | 86 (72.9%) | 32 (27.1%) | | 1.008 | 0.9791 |
Student | 83 (85.6%) | 14 (14.4%) | | 1.978 | 0.0748 |
Retired | 111 (64.2%) | 62 (35.8%) | | 1.498 | 0.1147 |
Disabled | 30 (56.6%) | 23 (43.4%) | | 0.784 | 0.488 |
Unemployed | 90 (62.1%) | 55 (37.9%) | | 0.97 | 0.9108 |
Refuse to answer | 6 (46.2%) | 7 (53.8%) | | 0.902 | 0.8776 |
Employment under COVID-19 | (n = 527) | | 0.2094 | | |
The same (it has not changed after COVID-19 emergency) | 297 (72.4%) | 113 (27.6%) | | | |
I lost my job during the emergency | 51 (75.0%) | 17 (25.0%) | | | |
I’m laid off until further notice | 30 (61.2%) | 19 (38.8%) | | | |
N/A | 320 (66.5%) | 161 (33.5%) | | | |
Refuse to answer | 6 (75.0%) | 2 (25.0%) | | | |
Income | (n = 970) | | 0.0201 | | |
Less than $10,000 | 264 (70.6%) | 110 (29.4%) | | (ref) | (ref) |
$10,000-$19,999 | 126 (68.1%) | 59 (31.9%) | | 1.16 | 0.5313 |
$20,000-$34,999 | 145 (66.5%) | 73 (33.5%) | | 0.945 | 0.8263 |
$35,000-$49,999 | 50 (64.1%) | 28 (35.9%) | | 1.048 | 0.8908 |
$50,000 or more | 95 (82.6%) | 20 (17.4%) | | 2.677 | 0.0055 |
Refuse to answer | 24 (52.2%) | 22 (47.8%) | | 0.721 | 0.3936 |
What is your sex assigned at birth? | (n = 1016) | | <0.0001 | | |
Woman | 496 (64.7%) | 271 (35.3%) | | (ref) | (ref) |
Men | 208 (83.5%) | 41 (16.5%) | | 2.583 | 0.0001 |
What is your sexual orientation? | (n = 995) | | <0.0001 | | |
Heterosexual | 525 (66.4%) | 266 (33.6%) | | (ref) | (ref) |
Homosexual | 112 (81.8%) | 25 (18.2%) | | 0.895 | 0.7228 |
Bisexual | 48 (85.7%) | 8 (14.3%) | | 2.113 | 0.0747 |
Other | 10 (90.9%) | 1 (9.1%) | | 3.441 | 0.247 |
Refuse to answer | 9 (42.9%) | 12 (57.1%) | | 0.439 | 0.1165 |
What is your current marital status? | (n = 999) | | <0.0001 | | |
Single, never married | 281 (79.2%) | 74 (20.8%) | | (ref) | (ref) |
Currently married, living with partner | 295 (66.6%) | 148 (33.4%) | | 0.751 | 0.1863 |
Separated/divorced | 99 (61.5%) | 62 (38.5%) | | 0.708 | 0.1953 |
Widowed | 20 (50.0%) | 20 (50.0%) | | 0.458 | 0.0637 |
Refuse to answer | 9 (52.9%) | 8 (47.1%) | | 0.685 | 0.5258 |
Health region | (n = 937) | | 0.0002 | | |
San Juan metro area | 459 (73.8%) | 163 (26.2%) | | (ref) | (ref) |
Other | 195 (61.9%) | 120 (38.1%) | | 0.647 | 0.0084 |
[Missing] | 50 (63.3%) | 29 (36.7%) | | 0.731 | 0.2849 |
Number of people living together | n | 683 | 295 | | | |
Mean (SD) | 2.1 (1.5) | 2.1 (1.5) | 0.2164 | | |
Number of children living together | n | 656 | 278 | | | |
Mean (SD) | 0.5 (0.8) | 0.6 (1.5) | 0.0822 | | |
Risk Factor Count | (n = 1011) | | 0.3365 | | |
0 | 330 (71.0%) | 135 (29.0%) | | | |
1 | 200 (65.8%) | 104 (34.2%) | | | |
2 | 111 (72.1%) | 43 (27.9%) | | | |
3–6 | 58 (65.9%) | 30 (34.1%) | | | |
Refuse to answer | 5 (100.0%) | 0 (0.0%) | | | |
Number of Risk Factors Reported | N | 699 | 312 | | | |
Mean (SD) | 0.9 (1.1) | 0.9 (1.1) | 0.7107 | | |
How do you consider the government of Puerto Rico’s response to the coronavirus pandemic? | (n = 1014) | | 0.0612 | | |
Excellent/Good | 147 (74.2%) | 51 (25.8%) | | (ref) | (ref) |
Regular | 274 (71.0%) | 112 (29.0%) | | 0.636 | 0.0379 |
Bad/Very bad | 282 (65.6%) | 148 (34.4%) | | 0.372 | <0.0001 |
Refuse to answer | 1 (50.0%) | 1 (50.0%) | | 0.633 | 0.757 |
How worried are you about the impact that COVID-19 can have on you? | (n = 1015) | | <0.0001 | | |
Extremely worried/Very worried | 547 (72.1%) | 212 (27.9%) | | (ref) | (ref) |
Somewhat worried | 132 (67.3%) | 64 (32.7%) | | 0.656 | 0.027 |
Just a little bit worried/I’m not worried | 25 (41.7%) | 35 (58.3%) | | 0.196 | <0.0001 |
Refuse to answer | 0 (0.0%) | 1 (100.0%) | | - | 0.9791 |
Table 2.
COVID-19 Knowledge Acquisition and Perceptions of Vaccine Acceptability.
Table 2.
COVID-19 Knowledge Acquisition and Perceptions of Vaccine Acceptability.
Variable (N, %) | If There Existed an Approved Vaccine to Prevent the Coronavirus Infection, How Likely is It that You Would Get Vaccinated? |
---|
High Likelihood | Low Likelihood | p-Value |
---|
How confident are you in your ability to determine if the information you are receiving about COVID-19 is correct? | (n = 1007) | | 0.0011 |
Super confident | 288 (76.2%) | 90 (23.8%) | |
Somewhat confident | 366 (65.5%) | 193 (34.5%) | |
Not confident at all | 44 (62.9%) | 26 (37.1%) | |
Refuse to answer | 6 (66.7%) | 3 (33.3%) | |
What sources do you trust to obtain reliable information regarding COVID-19? * (select all, n = 1016) |
Social media | 303 (43.0%) | 121 (38.8%) | 0.2043 |
TV commercials | 155 (22.0%) | 63 (20.2%) | 0.5134 |
News programs | 358 (50.9%) | 156 (50.0%) | 0.8021 |
Peer network | 115 (16.3%) | 34 (10.9%) | 0.0238 |
Healthcare professionals | 495 (70.3%) | 186 (59.6%) | 0.0008 |
National/international health organizations | 525 (74.6%) | 174 (55.8%) | <0.0001 |
Local health department | 349 (49.6%) | 137 (43.9%) | 0.0955 |
Other | 39 (5.5%) | 12 (3.8%) | 0.2541 |
I don’t believe any source of information about COVID 19 | 3 (0.4%) | 11 (3.5%) | 0.0001 |
Refuse to answer | 5 (0.7%) | 5 (1.6%) | - |
| Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. |
© 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).