{'fraction_non_alphanumeric': 0.035054268113816366, 'fraction_numerical': 0.021633910237606337, 'mean_word_length': 5.047450110864745, 'pattern_counts': {'":': 0, '<': 7, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Acceptance of COVID‐19 booster vaccination based on the protection motivation theory: A cross‐sectional study in China

Abstract The promotion of the booster shots against severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) infection is an open issue to be discussed. Little is known about the public intention and the influencing factors regarding the booster vaccine. A cross‐sectional survey in Chinese adults was conducted using an online questionnaire, which designed on the basis of protection motivation theory (PMT) scale and vaccine hesitancy scale (VHS). Hierarchical multiple regression was used to compare the fitness of the PMT scale and VHS for predicting booster vaccination intention. Multivariable logistic regression was used to analyze the factors associated with the acceptance. Six thousand three hundred twenty‐one (76.8%) of participants were willing to take the booster shot. However, the rest of the participants (23.2%) were still hesitant to take the booster vaccine. The PMT scale was more powerful than the VHS in explaining the vaccination intention. Participants with high perceived severity (adjusted odds ratio [aOR] = 0.69) and response cost (aOR = 0.47) were less willing to take the booster shots, but participants with high perceived susceptibility (aOR = 1.19), response efficacy (aOR = 2.13), and self‐efficacy (aOR = 3.33) were more willing to take the booster shots. In summary, interventions based on PMT can provide guidance to ensure the acceptance of the booster vaccine.


| INTRODUCTION
The coronavirus disease 2019  pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), remains a severe challenge worldwide. As of April 7, 2022, there were over 494 million confirmed COVID-19 cases and over 6.17 million deaths. 1 Mass vaccination is one of the potential measures to stop the COVID-19 pandemic by establishing the herd immunity against SARS-CoV-2 infection. 2 Increasing evidence has showed that the COVID-19 vaccines were safe and efficacious against SARS-CoV-2 infections. 3 But the infected cases were frequently reported even after receiving two doses of COVID-19 vaccines, which termed as "breakthrough infections" and have raised a critical issue. Thus, current vaccination strategy might be not sufficient to establish a strong barrier against SARS-CoV-2 infections. 4,5 The reasons for the emergence of breakthrough infections are still under investigation. One of the explanations is the rapid decline in antibody titers overtime after vaccination. 6  Africa, further exacerbates the risk of breakthrough infections. 5,7 Recent clinical studies have demonstrated that the third and fourth doses of inactivated vaccine or mRNA vaccine significantly reduced the rates of confirmed COVID-19 and severe illness. 8 In addition, other studies showed that the booster vaccination effectively increased the titers of neutralization antibodies against SARS-CoV-2 variants. 9,10 Consequently, the administration of another additional shot (thereby termed as the booster vaccination) is proposed to maintain and improve the effectiveness of COVID-19 vaccines. 11 The acceptability of routine doses of COVID-19 vaccination had been extensively investigated in different countries and population. [12][13][14][15] However, little is known about the public intention regarding the additional booster vaccination and the factors that influence this willingness.
Protection motivation theory (PMT) is often used to explain how individuals adopt protective measures against different diseases. 16 PMT is a type of social cognition theory that includes the following constructs: perceived severity, perceived susceptibility, response efficacy, self-efficacy, and response cost. 17 The PMT is usually used to predict the motivation of individuals towards self-protective. In addition, the vaccine hesitancy scale (VHS) developed by the World Health Organization Strategic Advisory Group of Experts is commonly used to identify hesitation in different situations based on factors such as confidence, complacency, and risk. 18 Previously, these measuring tools had been applied to the evaluation of COVID-19 vaccination intention, 19 (1)

| Booster vaccination intention
The intention to receive the booster COVID-19 vaccine was measured depending on the answer of the question "To what extent do you want to take the booster COVID-19 vaccine?," and scored by "definitely yes," "unsure but tend to be willing," "unsure but tend to be unwilling," "definitely no." The responses to COVID-19 vaccine intention were classified into two categories: willing group (definitely yes, unsure but tend to be willing) and unwilling group (unsure but tend to be unwilling, definitely no). Participants in the willing group were further asked about the reasons why willing to take a booster vaccination. Participants in the unwilling group were further asked to answer "Why don't you want a booster shot?." Hesitation, delay, or refusal to receive the COVID-19 booster shots was defined as VH.

| PMT scale
The PMT scale in this study consisted of five dimensions, including the perceived severity to COVID-19 (three items), the perceived susceptibility of COVID-19 (three items), the response efficiency (three items), the self-efficacy (three items), and the response cost (two items). This scale was adapted from previous studies. 19,29,30 Participants were asked about how they agreed with each statement, and a 5-point Likert-style scale was used to score each item, with a range from strongly disagree (1 point) to strongly agree (5 points). A higher score on each item indicates a higher level of threat appraisal, response efficacy, self-efficacy, and response cost, respectively.
Reliability analysis showed that the total Cronbach's α of this PMT scale was 0.77, and the Cronbach's α of the five dimensions was 0.82, 0.93, 0.87, 0.86, and 0.80, respectively (Table 1).

| VHS
In this study, the VHS was adapted from previous studies. 18,31 This scale consisted of three dimensions: complacency (three items), convenience (three items), and confidence (four items). This scale also used a 5-point Likert scale to score items, from strongly disagree (1 point) to strongly agree (5 points). A higher score indicated a more negative attitude toward COVID-19 vaccination. Total VH scale Cronbach's α was 0.86.
Exploratory factor analyses were conducted on the scores of PMT and VH scales, and the results indicated that both scales had high validities as well as high reliability (Supporting Information: Table S1).

| Data analysis
Cronbach's α values and confirmatory factor analysis were performed to test the reliability and validity of the two scales. confidence interval (CI) were used to quantify the effects. All analyses were performed by SPSS26.0 (IBM Corporation). The alpha level was 0.05, and p < 0.05 was considered statistically significant. 3 | RESULTS
The male participants and health care staff were significantly more willing to receive the booster vaccination than those who were female (p < 0.001) and nonmedical staff (p < 0.001). Participants who did not feel uncomfortable after vaccination (p < 0.001) and had an interval of more than 6 months after last vaccination (p < 0.001) were more likely to accept the booster vaccination. The intention to vaccination was highest for those in junior high school or below (p < 0.001). In addition, those who take active attention to news about the COVID-19 pandemic at least once a day had the highest proportion of intention to accept the booster vaccination (p < 0.001) ( Table 2).

| Contribution of PMT and VH scale in predicting the intention to receive the booster vaccine
Taking the intention of "receive the vaccine boosters" (range:

| The predicted factors to affect the booster vaccination intention
Taking the average score of each construct among all participants as the classification criteria, the scores of the participants in each construct in PMT scale were divided into "low scores" and "high scores." The score levels of five constructs were taken as the independent variables, and the "willing" or "hesitant" of the booster vaccination was taken as the dependent variable for multivariable the contrary, the participants with higher scores of "perceived susceptibility" (aOR = 1.19, 95% CI: 1.61-1.34), "response efficacy" (aOR = 2.13, 95% CI: 1.83-2.49), and "self-efficacy" (aOR = 3.33, 95% CI: 2.83-3.93) were more likely to "be willing to receive the booster vaccination" (Table 5).

| DISCUSSION
The VH increases the difficulty of achieving herd immunity and has a negative impact on the prevention and control of infectious diseases. 32 Although the COVID-19 pandemic has been effectively controlled in China, it remains extremely vulnerable to the imported SARS-CoV-2 transmission. 33  PMT scale is usually used to predict the motivation of individuals towards self-protective measures. We modified the PMT scale in this study, based on people's judgment on the pandemic as the threat appraisals and people's understanding of taking booster vaccination as the coping appraisals. Of note, we found that this modified PMT scale was better to explain the differences in the participants' intention to receive the booster vaccination than that of the VH scale. In this study, our results of the PMT scale showed that coping appraisals, including response efficacy, self-efficacy, and response cost, were the key factors determining the COVID-19 booster vaccination behavior. The aOR of response efficacy and self-efficacy were 2.13 and 3.33, respectively, indicating that there was a higher intention of the booster vaccination, when participants have a higher belief in the booster vaccination and a higher confidence to take self-protective measures. In addition, the aOR value of response cost was 0.47, suggesting that the higher perception of adverse health costs with vaccination might be associated with the lower intention of the booster vaccination. Our results on the coping appraisal were consistent with a previous study on hepatitis B vaccination intention, which reported that the vulnerability, response efficacy, and self-efficacy were the determinant factors associated with the intentions. 29 As for the threat appraisals, our study showed that perceived severity and perceived susceptibility had different influence on the intention to receive the booster vaccination. A higher level of perceived susceptibility was associated with a higher intention of the booster vaccination, which is consistent with the previous study that The COVID-19 pandemic has lasted for more than 2 years, and the prevention and control of this pandemic have become a complex system in a globally connected world. Among them, VH and vaccine inequity are two major issues in the mass vaccination strategy for COVID-19 control. 46 To some extent, VH and vaccine inequity are correlated with the local level of economy, health service, and production capacity. 47 An in-depth understanding of people's attitude to booster shots would not only improve vaccination coverage in different regions but also increase incentives to expand production scale and develop a novel generation of vaccines for vaccine manufacturers, which will be helpful to reduce the social inequities and rehabilitate the social economy.

| STRENGTHS AND LIMITATIONS
In this study, a comprehensive analysis and comparison with a large sample size were performed for the study design and the selection of the measuring scale. To our best knowledge, this study is the first time to simultaneously use PMT and VHS to investigate booster vaccination intentions, and we found that the PMT scale was more powerful than the VH scale in explaining the results of vaccination intention. However, there are still some limitations in our study. First of all, this investigation was conducted through an online questionnaire, using a snowball sampling method, and thus there might be a selection bias of sampling. For example, some people without smartphone and internet access might fail to participate in this survey. Second, it was difficult to guarantee the authenticity of the answers since we did not conduct the survey face-to-face, though we set up quality control questions. Finally, the intention of the booster vaccination may be dynamically changed with the epidemic situation.
Therefore, these findings may not fully reflect the latest intention of the Chinese population to take the COVID-19 booster vaccine.

| CONCLUSIONS
Overall, our study demonstrated that there was a high intention to receive the COVID-19 booster vaccine but quite a few people were still hesitant in Chinese adults. Of note, the PMT scale was powerful to study the vaccination intention. These data suggested that the PMT scale could be used not only to understand the intention of receiving the COVID-19 booster vaccine in a certain population but also to develop appropriate interventions to improve people's vaccination intention.

ACKNOWLEDGMENTS
We thank all members for carefully reading and commenting on the manuscript. We thank staff members at disease control institutions across Guangdong province for helping us to collect questionnaires. We are grateful to all participants for taking part in this investigation. This study was supported by grants from the National Natural Science

Foundation of China (81971927) and the Science and Technology
Planning Project of Shenzhen City (JSGG20200225152008136, 2019 0804095916056). All funding parties did not have any role in the design of the study or in the explanation of the data.