1. Introduction
Since the outbreak of the COVID-19 (coronavirus disease 2019) pandemic in December 2019, nearly every country worldwide has suffered greatly over a long period of time. To combat COVID-19, the general public, professionals, and authorities have made tremendous efforts and devised multiple strategies to prevent the transmission of SARS-CoV-2 [
1]. Among these strategies, vaccination is considered as one of the most effective methods to control the pandemic [
2].
However, many people are hesitant regarding the COVID-19 vaccine. SAGE (The Strategic Advisory Group of Experts on Immunization) defined vaccine hesitancy as a “delay in acceptance or refusal of vaccines despite availability of vaccine services” [
3]. Vaccine hesitancy has been identified as one of the ten greatest threats to public health by the World Health Organization [
4]. Therefore, exploring and identifying factors that influence people to vaccinate against COVID-19 are high-priority tasks [
5].
Young adults are a significant group to be concentrated on for the promotion of immunization campaign. Young people are vulnerable to coronavirus infection due to jobs and campus life [
6]. Moreover, the young population plays an important role in virus transmission given the fact that they have high rates of asymptomatic infections and have active social lives [
7]. Besides, the period of young adulthood experiences changes in personal values and beliefs [
8], which may have influences on the adherence to preventive behaviors [
9]. Considering the high frequency of social media use among young people and their tendency to seek health information online, their vaccine attitudes may be easily affected by social influences [
10]. Furthermore, young adults could also work as potential change agents and promote safer behaviors within their families and communities [
11]. In this study, we aim to explore influencing factors related to COVID-19 vaccine willingness among young adults in China.
Many factors that would influence the COVID-19 vaccination intention of young adults were identified, such as concerns about vaccine safety [
12,
13,
14], side effects [
11,
12], effectiveness [
11,
13,
15], political concerns [
11,
14], thinking others are in greater need of the vaccine [
12,
15,
16], and social support [
8]. Researchers conducted a cross-sectional survey among Chinese college students and found that participants who believed in vaccine safety and effectiveness in preventing infection were more likely to accept the COVID-19 vaccine [
17]. Besides, a cross-sectional study, based on the extended theory of planned behavior, surveyed mainland Chinese university students and reported that knowledge about the COVID-19 vaccine as well as the risk perception of COVID-19 were main factors influencing COVID-19 vaccine attitude [
18]. Moreover, a study based on the health belief model conducted interviews among young adults in China and proposed that social benefits and worry reduction were positive factors of vaccination intention [
19]. Other factors for Chinese young adults included worrying about adverse effects [
20], vaccine safety [
17], family support [
21], and attitudes of surrounding individuals [
22]. Although there were many studies on COVID-19 vaccination willingness, the subjective experience of young adults was insufficient in research. Many studies used questionnaires to survey individuals, and participants may not explicate the reasons of their responses in detail in most cases. Exploring the experiences and opinions of young adults in an explicit and flexible way may further the understanding of vaccination intention. Furthermore, semi-structured interviews may provide participants the opportunity to adequately express their responses using their own narratives. In addition to the common qualitative analysis methods, we propose that multiple analysis methods may help identifying potential promising factors from different viewpoints. From the perspective of young adults, this study aims at exploring lived experiences related to COVID-19 vaccination intention.
Researchers described health behavior as “any activity undertaken by a person believing himself to be healthy, for the purpose of preventing disease or detecting it in an asymptomatic stage” [
23]. Furthermore, getting vaccinated could be considered as health behavior, which is also acknowledged in many relevant studies [
24,
25,
26]. A theory related to health behaviors is needed to identify factors affecting vaccination in this study. Multi-theory model (MTM) is a fourth-generation theory explaining changes in health behaviors, which includes malleable constructs and can provide insights for both one-time and long-term behavioral changes [
27]. MTM incorporates multiple theoretical perspectives and could work at individual, group, and community levels [
27]. Considering vaccination uptake is a complex issue involving multiple factors and complicated contexts, MTM could be used to explore such a phenomenon from a comprehensive and extensive perspective. MTM consists of two components: initiation and sustenance, which differentiates between these two components in a detailed way and provides a nuanced understanding of health behaviors. Since vaccination differs from long-term behaviors, such as physical activity, we have chosen to focus on the first component in our study. Initiation is explained in terms of three constructs: participatory dialogue, behavioral confidence, and changes in the physical environment [
27]. MTM has been used by previous studies to explain health behaviors changes. For instance, a cross-sectional study based on MTM explored COVID-19 booster vaccination hesitancy in the United States and found that the hesitant group had lower odds of behavioral confidence than the non-hesitant group [
28]. Researchers also used MTM to explain the handwashing behavior in an American sample of college students during the COVID-19 pandemic [
29] as well as the intentions of physical activity behavior among Chinese pregnant women [
30]. In the present study, we proposed to use this framework to explore COVID-19 vaccination intentions in China.
With MTM working as the theoretical basis, this study focused on the subjective experience of individuals and explored what factors might be able to tip the scales toward a decision among young adults in China who are initially hesitant to get vaccinated. Specifically, we conduct semi-structured interviews for data collection and employ qualitative thematic analysis and machine learning approach to analyze data.
3. Results
In this study, we carried out 12 interviews.
Table 1 showed the demographic information of our interview participants. The gender distribution of participants reached a balanced gender ratio. Besides, the regional distribution was rather diverse.
3.1. Thematic Analysis Results
After concluding all interviews, we used three constructs in MTM as a framework and conducted thematic analysis to analyze interview transcripts. Thirty-one initial codes were generated (for more details, please refer to the
Appendix A Table A1) and nine key factors were identified. More specifically, we identified four key factors belonging to participatory dialogue, one key factor that was closely related to behavioral confidence, and two key factors pertaining to changes in the physical environment. Besides, we found two novel key factors beyond MTM. The final interview results are shown in
Table 2.
The main content of participatory dialogue focused on the advantages and disadvantages of changes in health behavior [
27], including the
effectiveness and safety of vaccines, scientific and objective expression, perceived benefits, and
social responsibility.
The first factor is the effectiveness and safety of vaccines. This factor emphasized concerns regarding whether the vaccine would protect against COVID-19 effectively or whether it would pose a threat to personal safety. Participants reported that they were worried about the side effects of vaccination. Some participants wanted to know more about why some people were not suitable for vaccination.
Scientific and objective expression emphasized the fact that vaccine-related information should avoid the inclusion of arbitrary or ambiguous expressions, provide a comprehensive source of vaccination information from an objective perspective, and use accurate and easy-to-understand language. Some participants noted that they had heard that the effectiveness rate of COVID-19 vaccines in Brazil was low, and they believed that it was rather honest to publish such information instead of merely praising the vaccine.
Perceived benefits referred to the benefits perceived by individuals following vaccination. For example, participants noted that they would get vaccinated actively if doing so made it easier to enter and leave campus.
Social responsibility entails that people are aware, feel, and believe that an individual should be responsible for others, i.e., his or her family, group, country, and society. Moreover, such a person should also have the corresponding conscious attitude that an individual should abide by norms, accept responsibility, and fulfill obligations. Some participants indicated that vaccination uptake is a sign of being responsible to others and to society.
Our interview results identified this construct. The effectiveness and safety of vaccines and scientific and objective expression both focused on the disadvantages that people may face when considering vaccination uptake, such as side effects and limited efficacy. The perceived benefits emphasized the advantages perceived by individuals, while social responsibility underlined the advantages shared by the community and society.
Behavioral confidence emphasized the certainty of individuals when performing a certain behavior, such as receiving the COVID-19 vaccine. The source of behavioral confidence can come from external sources. For instance, people would refer to the opinions of influential people in real life [
27]. In this study, we confirmed one key factor,
External reference, in this construct.
External reference referred to situations in which an individual intended to engage in a certain behavior or develop a certain attitude by using a specific individual or group as a reference and object of comparison. These reference objects included specific social groups, the majority of people in the society, people surrounding the individual in question, and people from different political and cultural backgrounds. Some participants noted that the ways in which people around them viewed vaccines were important for them. If close friends and family chose to become vaccinated, these participants would also approve of the vaccine.
Changes in the physical environment emphasized the importance of individuals’ physical environment, including the availability, accessibility, and convenience of resources, which could also affect behavioral intentions. In this study, this construct contained two key factors, i.e., the convenience of vaccines and the perceived necessity and urgency of vaccination uptake.
The convenience of vaccines referred to the costs that individuals would be required to consider and pay during the process of vaccination, such as costs related to distance and time. Participants noted that if there were many vaccination sites and if it were convenient to get vaccinated, they would be more willing to receive the COVID-19 vaccine.
The perceived necessity and urgency of vaccination uptake emphasized the degree of intensity and urgency associated with the need for vaccination that individuals experienced in the context of the current social and epidemic situation. Several participants noted that if it were difficult to make a vaccination appointment or if the vaccine were scarce, they would be more willing to receive the vaccine.
In this study, we found that although other key factors cannot simply be integrated into MTM constructs, they were also important influencing factors related to COVID-19 vaccination intention. These factors included perceived threat to the freedom of choosing getting vaccinated and policy requirements.
Perceived threat to the freedom of choosing getting vaccinated referred to situations in which people felt some degree of threat to their freedom when certain acts aimed at persuasion interfered with individual free choice. Some participants indicated that many reports claimed that people must be vaccinated instead of that they should be vaccinated. This kind of expression made these participants more resistant to receiving the COVID-19 vaccine.
Policy requirements entailed that an individual would abandon his or her own opinion and behave in accordance with policy demands and group regulations. Some participants indicated that if the relevant authorities implemented mandatory vaccination against COVID-19, they would obey this requirement and become vaccinated.
3.2. Topic Modeling Results
To determine the appropriate number of topics for topic modeling, we calculated the coherence score for each topic model.
Figure 1 presents the coherence score result for each topic model, which was developed based on a different number of topics. We finally chose seven as the most appropriate number of topics for topic modeling based on two considerations. First, when the number of topics was set to seven, the coherence scores were high, thus indicating the good performance of the topic model. Second, our corpus was not very large, and too many topics could dilute the main focus of our text materials. Thus, in comparison with other numbers of topics that exhibited rather high coherence scores, such as sixteen and eighteen, seven contained the important topics to the greatest possible degree, on the one hand, and avoided the risk of confusing the main focus of the study, on the other [
48].
The inter-topic distance map is shown in
Figure 2. Each bubble in the inter-topic distance map represents a topic, and the area of the bubble indicates the prevalence of this topic [
49]. The distances of topics are scaled multidimensionally onto two axes [
50]. Relatively large and nonoverlapping bubbles in the map suggest a proper topic model result [
49]. Each bubble represents a different topic ranging from Topic 1 to Topic 7 in our study. The bubbles shown in
Figure 2 are relatively large and do not overlap, thus confirming the reasonability of using seven topics and suggesting that this approach produces a good topic model. The topics are ordered in descending order of prevalence in the corpus [
49].
Table 3 shows the results of the topic model including seven topics and the top twenty relevant words for each topic in the corpus. The numbers of topics are in accordance with the numbers shown in the inter-topic distance map.
Following the analysis and discussion of the seven topics grouped by topic modeling, we identified these seven topics as our final topic categories and reached an agreement concerning a label for each topic. This result is shown in
Table 4.
The first topic (Topic #1) was called influences from others’ experiences. This topic focused on the fact that people refer to the experiences and behaviors of other people, such as friends and colleagues, when making decisions regarding vaccination uptake. The feedback of others was of great value to these people.
The second topic (Topic #2) was labeled potential costs during the vaccination process. This topic included two aspects. One such aspect was the social pressure that people might experience if they remained unvaccinated. The other aspect pertained to the time and energy costs that people would pay if they were to consider becoming vaccinated. In other words, this topic concerned all the costs that people should consider when making a vaccination plan.
The third topic (Topic #3) was characterized as the side effects of the COVID-19 vaccine. This topic focused on concerns regarding the side effects of the vaccines. More specifically, this topic emphasized how people’s bodies would feel after becoming vaccinated, which caused them to worry.
The fourth topic (Topic #4) was labeled application range of vaccine. This topic focused on the application population and situations, that is, the kinds of people that were able to become vaccinated, the kinds of people that should wait, the kinds of people that should not receive a vaccination, and the situations in which vaccination would be useful, as well as those in which full vaccination would not be sufficient, thus requiring other epidemic protection approaches (e.g., a nucleic acid test).
The fifth topic (Topic #5) was defined as direct and transparent information. This topic emphasized the fact that the language and expressions used in relation to the vaccine should be unambiguous, direct, sincere, and transparent.
The sixth topic (Topic #6) was termed positive perceptions of the epidemic situation. This topic referred to the necessity of vaccination uptake, and when people felt positive regarding their living circumstances and believed that their risk of infection was low, they noted that they might be less willing to become vaccinated.
The seventh topic (Topic #7) was called safe and reliable information related to the COVID-19 vaccine. This topic emphasized people’s attention to trustworthy information related to vaccine safety. More specifically, official media, medical professionals, and scientific reports that supported and verified vaccine safety would have some degree of impact on certain people.
3.3. Influencing Factors Related to COVID-19 Vaccination Intention
From a practical perspective, we want to focus on the factors that have the greatest practical value in the context of vaccination promotion, and they can be divided into two categories: nonmanipulable and manipulable factors. Nonmanipulable factors refer to factors that are directly related to the COVID-19 vaccine itself, such as experimental results and objective data. Manipulable factors refer to factors that are indirectly related to the COVID-19 vaccine and commonly focus on external circumstances rather than information pertaining to the vaccine per se. It is rather easy for researchers to change the presentation of these factors in practice as a means of influencing the feelings of individuals.
Our two data analysis approaches used in this study led to two similar but subtly different results.
Table 5 shows the detailed findings of each analysis method.
With respect to the theme “nonmanipulable factors”, the thematic analysis identified one key factor, the effectiveness and safety of vaccines. The topic model identified two key factors, i.e., the side effects of the COVID-19 vaccine and application range of vaccine. We found that topic modeling confirmed more factors than thematic analysis. Moreover, the effectiveness and safety of vaccines and the side effects of the COVID-19 vaccine shared a partially similar focus, as the safety referenced by the former factor and the side effects noted by the latter factor both emphasized the perceived threat of vaccines and the damage that they can cause. However, application range of vaccine emphasized the relevant situation and the groups to which vaccines should or should not apply. This factor indicated a semantic connection between the targeted group and the situation of use, which differed from a concentration on the effectiveness and safety of vaccines and indeed supplied a new perspective concerning nonmanipulable factors.
As manipulable factors, the thematic analysis identified eight key factors, that is, convenience of the vaccine, social responsibility, external reference, perceived necessity and urgency of vaccination uptake, perceived threat to the freedom of choosing getting vaccinated, perceived benefits, scientific and objective expression, and policy requirements. The topic model identified five key factors: influences from others’ experiences, potential costs during the vaccination process, direct and transparent information, positive perceptions of the epidemic situation, and safe and reliable information related to the COVID-19 vaccine.
According to the meanings of these factors discussed above, we must acknowledge that influences from others’ experiences were quite similar to external reference, both of which highlighted influences from external sources. In addition, direct and transparent information and scientific and objective expression shared a common focus on the unambiguous and accurate language used to convey vaccine-related information. Moreover, potential costs during the vaccination process were also identified in the results of thematic analysis. In this topic, the first aspect, i.e., social pressure, was categorized as part of the external reference category in the thematic analysis. The second aspect, time and energy costs, was quite similar to the convenience of the vaccine emphasized by the thematic analysis. We also suggested that the safe and reliable information related to the COVID-19 vaccine factor found by the topic modeling was part of the external reference category in the thematic analysis. The former topic highlighted the importance of having reliable information sources, such as medical professionals, which was related to the latter factor.
In addition, one interesting finding was that the same factor was found by these two analysis results, but was presented in different directions between these two cases. The perceived necessity and urgency of vaccination uptake emphasized the fact that pressure and risks resulting from situations could cause people to feel a sense of urgency and to become more active in receiving the vaccination. Meanwhile, the positive perception of an epidemic situation highlighted the fact that a positive feeling toward the epidemic could decrease the public’s willingness to become vaccinated. Regardless of the direction, these two factors both pertained to the necessity of vaccine uptake.
In addition, the thematic analysis found social responsibility, perceived threat to freedom of choosing getting vaccinated, perceived benefits, and policy requirements, which were not included in the topic modeling results. These findings suggested that with respect to manipulable factors, the thematic analysis provided more detailed and distinct results compared to topic modeling.
Taking the results of both the thematic analysis and the topic modeling into consideration, we added application range of vaccine to the list of nonmanipulable factors based on the thematic analysis, and ultimately identified ten key factors related to COVID-19 vaccination intention.
4. Discussion
This study explored influencing factors related to public vaccination willingness based on semi-structured interviews. Following data collection, we employed two approaches to analyze the transcribed interviews. Using thematic analysis to code the transcripts manually, we identified seven key factors pertaining to the MTM constructs and included two novel influencing factors as supplements. We also used the topic modeling method LDA to examine the semantic pattern of the transcripts and thus identified seven key factors. Combining these two results, we analyzed the similarities and differences between them and confirmed ten influencing factors as a final set.
Some factors in this study have also been identified in previous research. In a systematic review by Wake, perceived risk of COVID-19, norms, the perceived benefits of the vaccine, the perceived efficacy of the COVID-19 vaccination, and COVID-19 vaccine safety concerns were found to be associated with COVID-19 vaccine uptake willingness [
51], thus confirming the rationality of our results. We suggest that these influencing factors may be effective generally for COVID-19 vaccine campaign. For mass immunization campaign, these factors may work as the focus of vaccine communication in the long term.
However, several factors identified by previous studies did not emerge in our study. Liu and Liu found that in the category of physical opportunities, monetary concerns could lead to the refusal of the vaccine [
52]. We did not find any factors related to affordability in our study. When the vaccine campaign began and the policy of free vaccinations was clearly announced [
53], some predetermined factors were no longer suitable to the new situation.
Besides, the role of choice of freedom among Chinese young adults deserved the attention in this study. A cross-sectional study conducted in Italy suggested that believing in the freedom to choose whether to vaccinate was the key predictor of people with vaccine hesitancy [
54]. However, in this study, we proposed that the perceived threat to freedom of choice may decrease the vaccination intention, and the perception of choice of freedom may be a motivating factor for immunization promotion. A previous study shared a similar idea that mandatory vaccination by employers would make people less likely to accept a COVID-19 vaccine [
55]. Our study further explored such an idea by providing narratives of participants and emphasized the importance of the role of freedom of choice.
This study used thematic analysis to analyze the interview data and employed topic modeling to supplement results. Our findings suggested that it is feasible to use thematic analysis as supplemented by topic modeling. In most cases, thematic analysis can provide detailed insights. The topics noted by the topic model were relatively rudimentary. However, topic modeling, as a method based on machine learning, can prevent oversights on the part of human beings facing high workloads and provide a novel perspective. According to our results, topic modeling indeed allowed us to identify some fresh relationships. Therefore, we suggest that future research should consider the addition of topic modeling to the thematic analysis to produce comprehensive analysis results.
Our study confirmed that MTM could function as a theoretical framework and explain influencing factors related to vaccination intention in China. Apart from the constructs associated with MTM, we also suggested novel factors as supplements. Our findings could provide nuanced understandings of related factors that can influence public COVID-19 vaccine uptake intention for young adults in China. By adopting semi-structured interviews, this study included the reflections and elaborations of participants sensitively and provided an insightful picture of effective factors related to COVID-19 vaccine hesitancy. Results might assist in determining the potential topics for targeted vaccination promotion programs. We suggest that authorities and public health workers may focus on one or several factors in accordance with the specific social situation and epidemic condition. For example, if the COVID-19 outbreak started in a country in close proximity to our own, authorities might consider emphasizing the severity of the disease and the risks faced by this country. Young people may thus feel the proximity of COVID-19, and their awareness of vaccination may be raised.
Our study faces certain limitations. First, our study was conducted in China, and our identification of influencing factors related to COVID-19 vaccine intention should thus be confined to China. People should use the results of this study with caution in the context of different cultural backgrounds. Besides, our study focused on the perspective of young adults. Little is known about whether these influencing factors found in this study would work well for the aged. Future study should further investigate the views of elderly people as well as other age groups. Further examination across generations may provide us with detailed information related to attitude changes concerning COVID-19 vaccine uptake. In addition, we suggest future researchers move forward to examine MTM framework and influencing factors confirmed in this study in a larger sample using epidemiological quantitative methods, which could expand the breadth of the framework and our findings. Besides, the differences of vaccination beliefs among different regions are worth being investigated in the future work. Although we made efforts to enrich the regional distribution, it is hard to derive the significant results due to the limited sample size in this study. We intend to further explore differences of effective influencing factors associated with COVID-19 on a regional level in a future study.