Introduction

COVID-19 remains a significant global threat, despite major efforts to combat it. Although early observations indicated that children were less likely to experience severe symptoms or be asymptomatic, recent data shows that COVID-19 has become a leading cause of death in children1. In addition, the infection can result in long-term consequences for children, including neurological issues, multisystem inflammatory syndrome, and myocarditis2,3,4. The impact on vital organs during childhood can lead to irreversible harm to a child's development. Therefore, it is essential to consider children a high-risk group and take measures to protect them from COVID-19.

Vietnam began vaccinating its population against COVID-19 in March 2021, and by July 2022, 81.3% of the population had received at least two doses5. Despite high coverage in adults, parents remain hesitant about vaccinating their children6. Studies found that knowledge about the severity of the disease, the benefits, and limitations of the vaccine, and trust in the government and healthcare system influenced parents' decisions1,7. Healthcare professionals are often viewed as trusted advisors and influencers of vaccine decisions8. However, vaccine hesitancy among healthcare professionals exists, which may lead to increased hesitancy among the general public9. It is, therefore, crucial to understand the factors that influence both healthcare professionals and the general public in their vaccine decisions.

Financing for COVID-19 vaccination is another critical issue that is not well understood. Most countries offer free vaccines, but changes in the global economy may result in the halt of free vaccinations, particularly in nations with low and medium incomes. In addition, the emergence of new immune evasive COVID-19 variants, such as the XBB 1.5 variant, requires the development of new vaccines10. The high rate of new variants may also necessitate annual COVID-19 boosters, similar to the annual flu shot11. Ensuring equal access to COVID-19 vaccination through appropriate financing is therefore an important issue that requires attention. As of June 15, 2022, Vietnam had administered over 224 million doses of COVID-19 vaccines. The coverage rates for the first and second doses among children aged 12–17 were approximately 100% and 97%, respectively. During this study period, the Ministry of Health of Vietnam accelerated the vaccination campaign for children aged 5 to under 12 years, aiming to ensure safety, efficacy, and complete vaccination for eligible children by the second quarter of 2022. The campaign also included the administration of booster doses (third dose) for children aged 5 to 17 who had completed the primary vaccination series. Efforts were intensified to promote and encourage the timely and full participation of children aged 5 to under 12 years in the vaccination program.

Behavioral theories can be used to explain the reasons for provider-user’s vaccine COVID-19 hesitancy. The Anderson and Aday model of healthcare utilization suggests that an individual's decision to get vaccinated may be influenced by their attitudes towards the vaccine, which about the vaccine's safety and efficacy, their perceived risk of COVID-19, and their access to and trust in healthcare providers12. The Theory of Planned Behavior suggests that an individual's decision to get vaccinated may be influenced by their beliefs about the vaccine's safety and efficacy, the social pressure they feel to get vaccinated, and their confidence in their ability to access and use the vaccine. The Social Cognitive Theory suggests that individuals may be influenced by their beliefs about the vaccine's safety and efficacy, their social networks and cultural beliefs, and their confidence in their ability to obtain and use the vaccine. However, evidence from assessments of both service providers and users in resource-limited settings is very limited. Meanwhile, policymakers need empirical data to make informed decisions, especially in the period of relaxing COVID-19 population measures13. In this study, we examined the willingness of healthcare professionals and public groups to vaccinate (WTT) and pay (WTP) for children's COVID-19 vaccination and identified the factors associated with their decisions. Using a Discrete Choice Experiment (DCE), we measure the importance of different vaccine characteristics and determine the optimal vaccine package for children14.

Results

The 891 individuals' demographic details are shown in Table 1. Approximately two-thirds were female (68.0%) and fell within the age range of 16–24 (74.9%). Most participants had a college/university (76.2%) and were single (81.5%). In addition, 18% of participants reported having at least one child. The most common income bracket was 128–425 USD (41.1%).

Table 1 Demographic characteristics of participants.
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Table 2 presents the COVID-19 and vaccination history of the participants. The majority of participants reported having contracted COVID-19 (59.8%) or having an adult family member infected (54.7%). A large portion of those who contracted COVID-19 had it within the past 3–6 months and was either relatively healthy or completely healthy. Approximately two-thirds were vaccinated with boosters (64.1%). The most common source of vaccine information was healthcare professionals (70.7%), followed by the media (40.4%).

Table 2 Personal and family history of COVID-19 infection and vaccination.
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Most participants (93.5%) would vaccinate their children for COVID-19, albeit at different levels depending on the children’s age (Table 3) HCP are significantly more likely to accept vaccination for children of all ages. The most common reason for not vaccinating children was "My child just got COVID-19" (39.7%), followed by "I want to wait for more information before deciding" (27.6%). A small but notable group of participants believed that COVID-19 vaccination was unnecessary, and that COVID-19 had disappeared (10.3%). 28.2% of respondents were prepared to pay half the cost of the COVID-19 vaccination for children, while 18% said they would not pay for it. Children's vaccinations were seen as an economic burden by a sizeable majority (60.7%).

Table 3 Willingness to take and willingness to pay for COVID-19 among healthcare professionals and the general public.
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The exploratory factor analysis of the variables influencing immunization to prevent illness is provided in Appendix S1. There were 2 factors: Factor 1 “Concerns on COVID-19 Vaccines and Responsibility of Vaccination” had 7 items, Mean = 6.83 (SD = 2.10), and Cronbach’s alpha = 0.89; Factor 2 “Vaccine Hesitancy and Fear” had 3 items, Mean = 5.39 (SD = 2.30), and Cronbach’s alpha = 0.84.

Regarding Interpersonal factors, 2 factors included: Factor 1 “Perceived COVID-19 Risk, Severity, and Impact” had 5 items, Mean = 7.16 (SD = 2.10), and Cronbach’s alpha = 0.87; Factor 2 “Service satisfaction” had 3 items, Mean = 7.07 (SD = 2.22), and Cronbach’s alpha = 0.91 (Appendix S2).

The factors associated with WTT and WTP for the COVID-19 vaccine for children in HCP are shown in Table 4. The results indicate that service satisfaction positively correlated with vaccine acceptance. Healthcare professionals were less likely to reject vaccination for young or all children if they are satisfied with the vaccination service (OR = 0.79; 95% CI 0.67; 0.94, and OR = 0.82; 95% CI 0.65; 1.03, respectively). Hesitancy towards vaccination for children from 5 to 17 years old was affected by participants’ child status (OR = 3.04; 95% CI 1.07; 8.66), and their concerns about the factors of the vaccine (OR = 1.24; 95% CI 1.01; 1.51). Having children already infected with COVID-19 increased their likelihood of only accepting vaccination for children aged 5–17 rather than all children (OR = 2.08; 95% CI 1.13; 3.85). Participants who fear the vaccine are more likely to reject children's vaccination altogether (OR = 1.71; 95% CI 1.23; 2.39). Interestingly, the financial burden was not identified as a factor affecting HCP’s decision to vaccinate children.

Table 4 Factors associated with the willingness to take and willingness to pay for COVID-19 vaccine for children in healthcare workers/medical students.
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Regarding financing for children's vaccination, the burden of medical expenses negatively correlated with HCP’s WTP for vaccination (OR = 0.34; 95% CI 0.22; 0.53). Inversely, better service satisfaction correlated with a higher level of WTP (OR = 1.16; 95% CI 1.01; 1.33). Fear of COVID-19 (OR = 0.78; 95% CI 0.69; 0.87), remote living areas (OR = 0.18; 95% CI 0.06; 0.52), and extended time after last COVID-19 infection (OR = 0.30; 95% CI 0.09; 0.93) were harmful factors that decreased the level of WTP. In contrast, greater concern about the vaccine and responsibility for vaccination (OR = 1.24; 95% CI 1.08; 1.43) and media as the vaccine information source (OR = 1.56; 95% CI 1.00; 2.42) were positive factors that increased participant’s willingness to pay for vaccination. Income level was not associated with WTP for children vaccine in healthcare professionals.

The factors associated with WTT and WTP for the COVID-19 vaccine for children among healthcare professionals (HCP) are shown in Table 4. The results from the Multinomial Logistic Regression model indicate that service satisfaction is positively correlated with vaccine acceptance. HCPs who are satisfied with vaccination services are less likely to reject vaccination for young or all children (OR = 0.79; 95% CI 0.67–0.94, and OR = 0.82; 95% CI 0.65–1.03, respectively). Hesitancy towards vaccination for children aged 5–17 is influenced by the participants’ child status (OR = 3.04; 95% CI 1.07–8.66) and concerns about vaccine factors (OR 1.24; 95% CI 1.01–1.51). HCPs with children who had already been infected with COVID-19 are more likely to accept vaccination only for children aged 5–17 rather than all children (OR = 2.08; 95% CI 1.13–3.85). Those who fear the vaccine are more likely to reject children's vaccination altogether (OR = 1.71; 95% CI 1.23–2.39).

Regarding the willingness to pay (WTP) for children's vaccination, analyzed using the Multivariate Ordered Logistic Regression model, the burden of medical expenses is negatively correlated with WTP (OR = 0.34; 95% CI 0.22–0.53). Conversely, better service satisfaction is associated with a higher level of WTP (OR = 1.16; 95% CI 1.01–1.33). Fear of COVID-19 (OR = 0.78; 95% CI 0.69–0.87), residing in remote areas (OR = 0.18; 95% CI 0.06–0.52), and a longer duration since the last COVID-19 infection (OR = 0.30; 95% CI 0.09–0.93) are factors that decrease WTP. In contrast, greater concern about the vaccine and responsibility for vaccination (OR = 1.24; 95% CI 1.08–1.43) and obtaining vaccine information from media sources (OR = 1.56; 95% CI 1.00–2.42) positively influence WTP. Income level was not significantly associated with WTP among healthcare professionals.

The factors associated with WTT and WTP for children receiving the COVID-19 vaccination among the general public (GP) are shown in Table 5. The Multinomial Logistic Regression model results indicate that a higher level of service satisfaction positively correlates with higher vaccine acceptance for young and all children (OR = 0.77; 95% CI 0.61–0.98 and OR = 0.81; 95% CI 0.72–0.92, respectively). Participants who were pregnant or had children were more likely to choose not to vaccinate children below 18 years (OR = 3.41; 95% CI 1.39–8.38) or only vaccinate children aged 5–17 (OR = 2.34; 95% CI 1.42–3.84). Respondents with concerns about the vaccine were more likely to opt out of vaccinating children below 18 (OR = 1.45; 95% CI 1.11–1.87) or only vaccinate children aged 5–17 (OR = 1.22; 95% CI 1.08–1.39). The time since COVID-19 infection also influenced decisions, with those infected over 6 months ago more likely to decline vaccination for young children.

Table 5 Factors associated with the decision to vaccinate and willingness to pay for the COVID-19 vaccine for children in the general public.
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In the Multivariate Ordered Logistic Regression model, the burden of medical expenses negatively correlated with WTP for vaccination (OR = 0.39; 95% CI 0.27–0.56), while better service satisfaction increased WTP (OR = 1.21; 95% CI 1.10–1.33). Surprisingly, participants with higher education levels exhibited lower WTP for the vaccine (OR = 0.52; 95% CI 0.34–0.80). Higher scores on concerns about COVID-19 vaccines and responsibility for vaccination negatively correlated with WTP (OR = 0.88; 95% CI 0.80–0.97). Participants with a monthly household income per capita higher than 3 million VND (> 128 USD) demonstrated higher WTP than those with less than 1 million VND (< 43 USD). Additionally, a time since COVID-19 infection of over 3 months also indicated higher WTP."

Table 6 demonstrates the optimal vaccine package generated from the DCE analysis. The ideal scenario for most participants included above 90% effectiveness with lifetime immunity, minor side effects, low mortality rate, and no limitations. For this scenario, participants' mean willingness to pay was 200.000 VND (8 USD). Figure 1 presents the feature importance of 6 vaccine attributes. The mortality rate was attributed to most concerned at 28.4 points, followed by immunity duration at 22.4 points and vaccine efficacy at 21.9 points. The cost of the least weighted characteristic is 7.4 points.

Table 6 Optimal vaccine package.
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Fig. 1
figure 1

Feature importance of attributes.

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Discussion

In this cross-sectional survey study of WTT and WTP for children's COVID-19 vaccination, we found that a large proportion of participants favored vaccinating children of all ages (72.4%). Vietnam’s vaccine acceptance rate was higher than countries such as Turkey (36%)15 and Germany (51%)16. Reasons for not accepting the vaccine include concerns about the vaccine attributes, fear of the vaccine, participants’ child status, and dissatisfaction with healthcare services. Regarding WTP, the most popular options were half-price, full-price, and free. The burden of medical expenses and service dissatisfaction reduced participants’ level of WTP. According to DCE, 200,000 VND was the ideal cost for children in the Vietnamese community to get the COVID-19 vaccination (approximately 8 USD), which was significantly lower than WTP in other countries (260 USD in the United States, 184 USD in Chile17,18). The disparity in WTP has been attributed to various factors such as per capita income, occupation, education level, and health environment19.

It is crucial for the WTT of both service providers and clients to have clear and accurate information about the seriousness of COVID-19 and the safety and effectiveness of the vaccination. Participants who declined to vaccinate their children cited perceived safety from the disease or a need for more information about the vaccine. When compared to non-parents, parents were shown to be more cautious in immunizing their kids, indicating that they believe the vaccine's hazards outweigh the dangers of contracting COVID-19. The widespread misconception that children are outsiders in the current COVID-19 pandemic needs to be urgently corrected20, as children can suffer from serious long-term complications of COVID-19 infections2,3,4, and they are potent disease carriers at school and in their homes21. While the speedy development of COVID-19 vaccine results from the combined effort of scientists, doctors, regulators, industry, and government, it also casts doubt in the public’s mind. Fear and concerns about the vaccine significantly contribute to vaccine hesitancy, with parents adopting a “wait-and-see” attitude or complete rejection of vaccination. To promote public acceptability of COVID-19 and its vaccination, the GP must have access to current information about these topics.

Our study identified HCP as a crucial vaccine information source for the public. According to studies, healthcare workers who choose to vaccinate their children are more likely to advise their patients to do the same, whereas those who choose not to vaccinate their children are less likely to do so9. While vaccine acceptance is high in HCP, it is concerning to see that a quarter of HCP demonstrate vaccine hesitancy at some level, with Vaccine Hesitancy and Fear being a significant factor. In addition, HCP are not immune to COVID-19 misinformation and can be influenced by informal sources of information, reducing their WTP. Similarly, Nowak et al. showed that greater trust in family and friends correlated with vaccine hesitancy22. As HCP are on the frontlines and are decisive in driving vaccination programs23, restoring their confidence in science and improving COVID-19 knowledge should be a priority in efforts to increase vaccination. It is vital to address worries and misconceptions regarding the COVID-19 vaccine, dispel them, and make the vaccine more readily available and easy for users in order to reduce vaccination hesitancy among users and providers. Healthcare providers may also benefit from additional education and training to increase their confidence and knowledge about the vaccine and its benefits.

WTP for children, COVID-19 vaccination is found to be an extension of WTT. Factors contributing to WTT, such as vaccine concerns and the perceived risk of COVID-19, also impact WTP. This finding implies that raising vaccination awareness will likewise raise consumers' willingness to pay. A substantial correlation between monthly household income per person and WTP was also discovered among the GP, as was previously shown in a number of other nations (Indonesia24, and Malaysia25). Since lower-income groups' WTP is partially related to financial factors, the economic situation of the target population should be considered in the development of vaccination programs.

Last but not least, service satisfaction is consistently a positive indicator of WTT and WTP for children vaccines among both HCP and GP. Several studies have demonstrated the relationship between customer satisfaction and vaccine acceptance26. Particularly, service quality and satisfaction influenced parents' decisions to accept vaccinations for their children due to the increased perceptions of safety and privacy27. Hedvall and Paltschik suggested that the professionalism and qualifications of medical staff have a tremendous impact on the service quality of healthcare facilities, and should be the focus of improvement28. These findings provide the foundation for healthcare administrators to improve vaccination facilities by fostering improved attitudes and knowledge of healthcare professionals.

Our study includes a number of limitations. Despite using a sizable sample of participants who resided in Vietnam, the online questionnaire might result in biased sampling because other provinces weren't represented. Second, the age group of 16–24 is overrepresented in our dataset. Many participants did not have children, so their lessened concern regarding the vaccine effect on children might have contributed to the higher vaccine acceptance rate. Third, the current free vaccine policy might affect participants’ answers to the questionnaire. Nevertheless, the result of this study should prove valuable for policymakers to understand the general trend in vaccination for children, which will hopefully lead to better vaccination programs in the future.

Conclusion

This study utilized the Theory of Planned Behavior and Social Cognitive Theory to identify factors influencing the willingness to vaccinate and willingness to pay for children's COVID-19 vaccination. Our findings underscore the significance of attitudes, social influence, and self-efficacy in vaccination decisions, aligning with the theoretical framework of these models. The results provide a comprehensive understanding of the factors affecting acceptance and payment for the COVID-19 vaccine for children, encompassing perspectives from both service providers and users. This understanding is crucial for achieving optimal vaccine coverage and herd immunity. The study suggests that providing accurate information about COVID-19 and its vaccine, along with ensuring high satisfaction with vaccination services, can significantly enhance both the willingness to pay and the willingness to vaccinate children. Healthcare professionals, as primary sources of information and service providers, play a pivotal role. Therefore, it is recommended that policymakers prioritize enhancing healthcare professionals' awareness and quality of care. Additionally, our study highlights the importance of leveraging public and government resources to effectively implement vaccination programs aimed at preventing severe infectious diseases, particularly in the context of the ongoing COVID-19 pandemic and potential future outbreaks.

Methods

Study design and sampling methods

In this research, data from Vietnam's Preference for Vaccine Evaluation and Trial (PREVENT) study was used. PREVENT was conducted through the Qualtrics platform and consisted of five separate datasets, each focusing on a different topic related to vaccines, including the COVID-19 vaccine for children, Monkeypox, the adult COVID-19 booster, the HIV vaccine, and a potential future pandemic. Participants answered a matching questionnaire after being allocated at random to one of these themes. Data validation was conducted using IP addresses, and the information was stored securely for research purposes. Participants gave informed consent by checking the box at the start of the questionnaire after being advised of the advantages and hazards of participation.

This cross-sectional study used snowball sampling, where 20 individuals were initially contacted to participate and then asked to refer others. The recruitment period was from April to August 2022, and a total of 5,700 Vietnamese individuals aged 16 and above from various regions of the country participated in the study. The data for the sub-study on the COVID-19 vaccination for children was completed by 891 of these participants. This analysis used primary data collected specifically for the study. The sampling randomly assigned respondents into different themes, resulting in an empirical dataset unique to this research. The study included two groups: the general public (GP) and healthcare professionals (HCP)/ medical students. Prior to taking part in the trial, each subject gave their informed permission after being made aware of the advantages and hazards.

Measurements and instruments

The Theory of Planned Behavior and Social Cognitive Theory were applied by including questions that assess attitudes towards the vaccine (safety and efficacy), perceived social pressure (influence from family and friends), and self-efficacy (confidence in accessing and using the vaccine). These elements were integrated to understand the multifaceted influences on vaccination decisions.

We searched the literature for elements that have been linked to COVID-19 vaccination payment and acceptability. From there, we built the initial list of questions as the tool with 4 major sessions: (1) Socio-demographics, (2) COVID-19 infection and immunization history, (3) Willingness to take COVID-19 vaccine for children, and (4) Willingness to pay for it. The questionnaire was developed based on a comprehensive literature review including studies on vaccine hesitancy, health behavior theories, and previous discrete choice experiments in the context of vaccination. A group of specialists in public health (2), infectious diseases (1), health services (1), econometrics (1), languages (1), target group representatives (4), and research assistants (2) later revised the questionnaire, translated it into Vietnamese, and pilot-tested it.

Variable definitions

Outcome variables

The participants’ willingness to vaccinate was determined by their choice of the three options: (1) Vaccinate all children, (2) Only vaccinate children 5–17, and (3) Do not vaccinate children. Additionally, the participant’s willingness to pay was determined by their choice of the five options: (1) No pay, (2) 20% fee, (3) 50% fee, (4) 80% fee, and (5) 100% fee. Participants' willingness to vaccinate and willingness to pay were defined as the proportion of participants willing or intending to receive a COVID-19 vaccine for themselves or their children, and the maximum price they were willing to pay for it.

Covariates

Socio-economic status was obtained from questions about age, sex, marital status, employment including healthcare workers/medical students and other jobs, monthly household income per capita, and present residence.

COVID-19 infection and immunization history included personal and family history of COVID-19 infection (time since infection, current health status) and vaccination.

Ten items, each representing two factors, were used to test the influence of the factors on vaccination to prevent illness. Responses to each question were measured by a 3-point Likert scale. The total score of all items within a factor was converted to a 10 scale. A higher score indicated greater community responsibility, dread of the vaccination, and heightened worry about the vaccine's characteristics. The Cronbach’s alpha of factors 1 and 2 was 0.89 and 0.84, respectively (Appendix S1). Factor 1: Concerns about COVID-19 Vaccines and Responsibility of Vaccination included 7 items. Factor 2: Vaccine Hesitancy and Fear included 3 items.

Interpersonal factors were measured by eight items, corresponding to two factors. Responses to each question were measured by a 3-point Likert scale. The total score of all items within a factor was converted to a 10 scale. A higher score denoted a greater chance of contracting COVID-19, a greater concern over the disease's effects on the economy and health, and better service satisfaction. The Cronbach’s alpha of factors 1 and 2 was 0.87 and 0.91, respectively (Appendix S2). Factor 1: perceived COVID-19 Risk, Severity, and Impact included 5 items. Factor 2: service Satisfaction included 3 items.

Discrete choice experiment: our literature review indicated that six primary attributes drive individual choices on vaccination: (1) Vaccine efficacy, (2) Immunity duration, (3) Side effects, (4) Mortality rate within 7 days after vaccination, (5) Restriction if not vaccinated, and (6) Costs. Each attribute was given 2–5 levels, making up 480 possible combinations (Appendix S3). Seven different scenarios based on the combinations were assigned to each participant. The DCE sample size was calculated using the Sawtooth Program29: Sample size = (multiplier*c)/(t*a) = 357. Where: multiplier = 1000, c = largest number of levels across all features (5), t = the number of tasks or questions (7), a = number of alternatives or choices per question (2). Both target groups surpassed this sample size, with 399 participants for HCP and medical students, and 491 participants for the GP.

Data analysis and statistical methods

We used Qualtrics and STATA software (v15) for statistical analysis. All variables were described using descriptive data. 141 missing records were eliminated after using the Listwise Deletion technique to clear up the missing data. Standard deviation (SD) and mean were used to represent continuous variables, whereas frequencies and percentages were used to represent categorical variables. Internal consistency was assessed using Cronbach’s alpha, with an acceptable value of 0.7 or above. The results of Exploratory Factor Analysis and Cronbach's alpha are presented in Appendices S1, S2.

Exploratory Factor Analysis with principal component analysis was used to determine the number of factors, using Scree plot, parallel analysis, total portion of variance explained, and eigenvalues. Items with ≥ 0.5 loadings were included in the relevant factor. The socio-economic, COVID-19 features, relevant information about the COVID-19 vaccine, variables impacting intention to vaccinate for disease prevention, and interpersonal factors were analyzed as covariates linked with WTT and WTP for the COVID-19 vaccination for children. We used two different regression models to analyze the data. The Multinomial Logistic Regression model was applied to compare the willingness to vaccinate (WTT) outcomes, specifically comparing 'Do not vaccinate children' and 'Only vaccinate children aged 5–17' against the reference category of 'Vaccinate all children'. This model helps identify the factors influencing these distinct vaccination choices. The Multivariate Ordered Logistic Regression model was used to assess the willingness to pay (WTP) for the COVID-19 vaccine, which was measured as an ordered categorical variable ranging from 'Unwilling to pay' to 'Full price'. This model allows us to evaluate the ordered nature of the WTP responses and the factors associated with varying levels of WTP. Each odds ratio (OR) in the tables indicates the likelihood of the specified outcome compared to the reference group. Models were then simplified using stepwise forward strategies, with only variables with p < 0.2 beings included. Statistical significance was determined by a P < 0.05.

To ascertain the relative significance of each investigated variable and create individual-based utility models for the DCE analysis, Hierarchical Bayes estimation utilizing the Bayesian approach was used. Contributions of each COVID-19 vaccine characteristic were calculated, and the optimal package for children's COVID-19 vaccination was identified.