https://orcid.org/0009-0007-4415-5855
ABSTRACT
Although COVID-19 vaccination was approved for younger children in Japan in October 2022, uptake rates remain critically low. This study aimed to investigate Japanese parents’ intentions, hesitators’ probability of positive intention change, and factors that motivate COVID-19 vaccination. Parents with a 6-month to 4-year-old child living in Japan participated in this internet-based, cross-sectional survey conducted from December 19, 2022, to January 4, 2023. The modified Poisson regression analysis was used to assess the probabilities of changing intention by each motivator when comparing the degree of hesitancy among hesitators, and the Poisson generalized estimating equations were used to compare the probabilities of changing intentions by potential motivators within hesitant individuals. Among 12,502 participants, 10,008 (80.1%) were hesitators. Parents with lower hesitancy levels were more likely to be motivated to vaccinate their children through potential motivators. Vaccine hesitators were motivated to vaccinate their children, particularly by proven vaccine effectiveness (including “protecting children from getting sick” with a probability ratio [PR] of 3.7 [95% confidence interval (CI) 3.5–3.9] and “less likely to infect adults” with a PR of 2.9 [95% CI 2.8–3.1]), as well as vaccine safety (including “safe vaccination of millions of children” with a PR of 3.1 [95% CI 3.0–3.3]) compared to injunctive norm (including “community leader recommendation”). Therefore, initially addressing parents with low hesitancy levels is an effective strategy that motivates COVID-19 vaccination. Also, providing evidence-based information about COVID-19 vaccine efficacy and safety that is consistent with parents’ needs is crucial.
Introduction
Vaccination is one of the most effective measures to mitigate the impact of COVID-19. COVID-19 vaccines were initially accessible to older age groups and healthcare professionals and gradually expanded to younger ages. Children generally exhibit mild symptoms; however, in some cases, they can occasionally experience a severe course of the disease, including subsequent complications, such as multisystem inflammatory syndrome in children (MIS-C).Citation1 Additionally, vaccinating children is important to prevent transmission in the community and reduce social and economic impact.
The Japanese government approved the COVID-19 vaccine for children aged over 6 months to 4 years in October 2022, and it has been available for free. Although WHO declared an end to COVID-19 as a global health emergency in May 2023, the Japan Pediatric Society announced that they still recommend the COVID-19 vaccination (primary series and booster at appropriate times) for all children over 6 months in October 2023.Citation2 The main reasons for the recommendation are that the spread of infection is expected to continue due to variant strain, about half of the population living in Japan is uninfected, and there have been severe cases and deaths of children due to COVID-19 in Japan.Citation2 Despite high primary series COVID-19 vaccination coverage of 92.7% among adults aged 65 years and older, it declines with age, at 6 months to 4 years old, and remains critically low at 3.1% (as of November 2023).Citation3 Previous studies of parents of 0 to 15-year-old children in Japan have reported that the parents’ concerns about side effects and their doubts about the effectiveness and safety of the vaccine were reasons for hesitation to get their children vaccinated against COVID-19.Citation4,Citation5 However, it was still unknown what percentage of parents were hesitant to vaccinate their 6 months to 4 years old children after the vaccine approval in Japan.
Vaccine hesitancy, defined as the delay in accepting or refusing vaccines despite their availability,Citation6 has been identified as a major obstacle preventing comprehensive coverage against the COVID-19 pandemic. Vaccine hesitancy occurs on the continuum between unclear vaccine demand and complete vaccine refusal.Citation7 Previous research on vaccine attitude change suggests that it is difficult to influence vaccination refusers and that direct attempts can have counterproductive effects.Citation8 We believe that the likelihood of changing COVID-19 vaccination intentions varies depending on the degree of hesitancy, and an effective strategy to reduce vaccine hesitancy should be developed.
In a recent systematic review of 108 studies, COVID-19 vaccine hesitancy rates for children aged up to 12 years were reported very widely, ranging from 0.69% to 89.6%.Citation9 Additionally, various related factors of childhood COVID-19 vaccination among parents have been observed worldwide; however, they are heterogeneous and context-specific.Citation9–12
Behavioral and social drivers of the vaccination framework, which focus on factors potentially changeable by the program, showed that “Thinking and feeling” and “Social processes” influence the vaccine motivation (intention).Citation13 One of the factors that comprise “Thinking and feeling” is confidence in vaccine effectiveness and safety, and “Social processes” include social norms. The following two types of norms are relevant to social norms: injunctive norms (e.g., authority’s recommendation) and descriptive norms (e.g., behaviors of close friends and family members). Although some factors have inconsistent findings of positive or negative effects on vaccination (e.g., higher educational level and higher income),Citation10 confidence in vaccine effectiveness and safety, as well as social norms, particularly descriptive norms, are consistently reported as having a positive effect.Citation14,Citation15 However, limited knowledge exists regarding which factors mostly motivate vaccine-hesitant parents more.
Consequently, to inform future cost-effective and tailored strategies to increase COVID-19 vaccine uptake, it is crucial to understand Japanese parents’ intentions to vaccinate their children, the probability of positive intention change, and factors that potentially motivate COVID-19 vaccination for children.
Therefore, this study aimed to determine the proportions of parental COVID-19 vaccine hesitancy for children aged 6 months to 4 years old living in Japan, examine if differences exist in the likelihood of changing COVID-19 vaccination intentions depending on the degree of hesitancy among vaccine-hesitant parents, and identify potential motivators influencing the vaccination decision among vaccine-hesitant parents. Specifically, we address the following research questions: 1) What percentage of parents are hesitant to vaccinate their children aged 6 months to 4 years with COVID-19? 2) Within the hesitant group, is there a difference in the likelihood of changing vaccination intention depending on the degree of hesitancy? 3) What potential factors could motivate parents in the hesitant group to vaccinate their children?
Materials and methods
Study design and setting
This cross-sectional internet-based survey using convenience sampling was conducted anonymously from December 19, 2022, to January 4, 2023. This was during the eighth wave of COVID-19, which had the highest recorded number of deaths,Citation16 and approximately 1 month after COVID-19 vaccination for children between 6 months and 4 years of age was available in Japan. This study was the first wave of the three-wave longitudinal investigation. The sample size of this study was 12,000, which conformed to that of a longitudinal study.
Participants and procedure
Parents aged 18–69 years old living in Japan who were raising at least one child aged 6 months to 4 years old were eligible to participate in this study. Data collection was charged by Cross Marketing Inc., Tokyo, Japan, a company with a survey panel of more than five million Japanese people registered.Citation17
Invitations were sent to registered parents in the panel with children under age 6 (N = 182,043). Invitation recipients answered screening questions, and respondents who were eligible and consented to participate were invited to complete a web-based questionnaire. The respondents answered questions using their electronic devices connected to the Internet. Recipients who did not respond were sent reminders. Data collection and reminders continued until the responses reached 13,000, considering the inclusion of inadequate responses. For study participation, respondents received credit points which can be used for online shopping and cash conversion. If respondents had more than one child within the target age, they were asked to limit their answers to the youngest child.
Measures
The questionnaire was pilot-tested among five parents who did not participate in the actual survey to assess clarity and readability. The survey was finalized based on the participant’s comments.
Demographic variables and others
Demographic factors included number of households, zip code of residence, parents’ gender and age, and child’s sex and age. Socioeconomic factors included job status, job type (health care provider/others), household income per year, level of educational attainment, and marital status. Other factors included parents’ COVID-19 vaccination status, the level of fear of COVID-19 (scores ranging from 7 to 35),Citation18 and current or previous COVID-19 infection of parents and children. Regarding parent information, respondents were asked to provide details about themselves.
COVID-19 vaccination behavior and parental intentions
The measure was adapted from previous similar studies.Citation19,Citation20 Respondents answered the question, “Has your child received at least one dose of the COVID-19 vaccination?” (yes or booked it already/no). If respondents answered “no,” they were asked, “Would you want your child to receive COVID-19 vaccination when it is available in your municipality?” (“Want my child to receive COVID-19 vaccination”/“Inclined to have my child vaccinated”/“Not sure about my child COVID-19 vaccination”/“Inclined not to have my child vaccinated”/“Do not want my child to receive COVID-19 vaccination”). We defined respondents who had already vaccinated their child, booked it, or answered, “Want my child to receive COVID-19 vaccination” or “Inclined to have my child vaccinated” as acceptors. After excluding acceptors, participants who answered “Not sure about my child’s COVID-19 vaccination,” “Inclined not to have my child vaccinated,” and “Do not want my child to receive COVID-19 vaccination” were classified as COVID-19 vaccine hesitators and assigned to groups “I,” “II,” and “III,” respectively.
Potential motivators for vaccination
A set of eight potential motivators for deciding to receive the COVID-19 vaccination for their children were shown to participants identified as COVID-19 vaccine hesitators. These motivators were developed based on previous research,Citation21 including vaccine effectiveness (such as the vaccine will help protect children from getting sick from COVID-19), safety (including millions of children have already been safely vaccinated against COVID-19), descriptive norm (for example, a close friend or family member vaccinated their children safely), and injunctive norm (e.g., public health authorities or community leader recommend children receive the vaccine). The list of all potential motivators can be found in . After each statement, respondents answered if this factor would make them “more likely to vaccinate,” “less likely to vaccinate,” or had “no impact on their decision.” When we performed the analysis, the three responses were merged into two categories, “more likely to vaccinate” vs. “other.”
Table 1. Full list of potential motivators.
Statistical analysis
Analysis was performed in three steps. First, descriptive analysis was conducted to identify the distribution of the COVID-19 vaccination behavior, parental intentions, and participants’ characteristics. Participants characteristics were summarized as number (%) and mean ± standard deviation for categorical and continuous variables, respectively, among whole participants (analysis set 1) and vaccine hesitators (analysis set 2).
Second, to assess the relationships between the degree of hesitancy (I – III) and the likelihood of changing parental vaccination intentions by each motivator among hesitators, we modeled the probabilities of positive intention change (i.e., answered more likely to vaccinate) using the “modified” Poisson regression with robust standard errors. The modified Poisson regression can directly estimate the outcome probability ratios (PRs), which would differ from odds ratios for outcomes with a probability of more than 10%,Citation22 as expected in this survey. Parent’s gender, educational attainment, household income, COVID-19 vaccination status, job type (health care provider vs. other), fear of COVID-19, parent’s and child’s current or previous COVID-19 infection, and child’s age were adjusted as the potential confounding variables based on published literature.Citation9–12 Subgroup analysis was performed based on parent’s gender, educational attainment, child’s age, and child’s history of COVID-19 to check the robustness of the result.
Third, to identify potential motivators influencing parental intention, we compared the likelihood of positive intention change by potential motivators by clustering individuals. Eight observations per individual, each corresponding to the response to one potential motivator for vaccination, were modeled using Poisson regression with generalized estimating equations (GEE) to account for the correlation within individuals. Here, positive intention change (i.e., more likely to vaccinate) (yes or no) served as an outcome variable, while dummy variables for eight potential motivators were the only independent variable because individual-level variables were balanced due to the same number of observations within individuals. Subgroup analysis was performed to assess the modification of the associations between vaccine hesitators groups (I – III). All statistical analyses were performed using R software (version 4.2.3, R Foundation for Statistical Computing, Vienna, Austria).
Ethical approval
The ethics committee of the Graduate School of Health Management, Keio University, approved this study (Approval number: 2022–20). Online informed consent was obtained from all participants.
Results
Sample selection and COVID-19 vaccination behavior and parental intentions
shows a flowchart of the study sample selection. Invitations were sent to 182,043 parents, and 34,200 answered screening questions (response rate: 18.8%). Among them, 13,317 respondents met the inclusion criteria and agreed to participate in the survey. We excluded respondents who did not follow simple instructions (e.g., “Please choose the second option from the bottom”) or who completed the survey quickly; we chose 2 min 40 seconds as a cutoff time. Finally 12,502 parents were included in analysis set 1. The analysis set 2 only included vaccine hesitators.
Figure 1. Flowchart of the study sample selection. aWe contacted parents who have a child under age of six.
shows parents’ COVID-19 vaccination behavior and intentions. Among 12,502 parents, 2,494 (19.9%) and 10,008 (80.1%) were acceptors and hesitators, respectively.
Table 2. COVID-19 vaccination behavior and intentions among parents with a child aged 6 months to 4 years.
Participants’ characteristics
shows characteristics of all participants and vaccine hesitators. Among all participants, 8,328 were female (66.6%), 12,137 (97.0%) had a spouse, and 7,488 (59.9%) were working. Approximately half of the children were boys and went to daycare or kindergarten during the daytime. Vaccine hesitators showed a similar distribution; however, the percentage of parent COVID-19 vaccination was lower than that of all participants. The prefectures where the respondents lived were representative of all prefectures in Japan (Supplementary Table S1).
Table 3. Characteristics of the participants.
Differences in the likelihood of positive intention change depending on the degree of hesitancy
Overall 10,008 vaccine hesitators (analysis set 2) were included in the following analysis. The associations between the degree of hesitancy and positive vaccination intention change by potential motivators among vaccine hesitators are shown in . For all potential motivators, the adjusted PRs for groups II and I were approximately two and three times higher than those for group III, respectively. The subgroup analysis results showed that larger PRs were observed in Groups I and II; in that order, those for group III in all analyses were consistent with those of the primary analysis (Supplementary Table S2).
Table 4. Association between the degree of hesitancy and positive vaccination intention change by potential motivators among vaccine-hesitant parents (analysis set 2; N = 10008).
Potential motivators’ effect on parental vaccination intentions
GEE estimates of PRs and 95% confidence intervals (CIs) of each potential motivator for positive vaccination intention change in the hesitant group are presented in . Compared with the community leader’s recommendation (Factor 8), all potential motivators significantly increased positive intention change. The large PRs (95% CIs) were observed for “The vaccine will help protect children from getting sick from COVID-19” with an estimate of 3.7 (3.5–3.9), “Millions of children have already been safely vaccinated against COVID-19” (3.1 [3.0–3.3]), and “Researchers determine that vaccinated children are less likely to infect adults” (2.9 [2.8–3.1]) in that order. In contrast, PRs (95% CIs) of 1.2 (1.1–1.2) for “Public health authorities recommend children receive the vaccine” was not much large. Subgroup analyses by degree of hesitancy showed that the top three and last two potential motivators based on estimated PRs remained unchanged (Supplementary Figure S1).
Figure 2. Association between potential motivators and vaccination intention changes among vaccine-hesitant parents (analysis set 2). Eight yes/no answers for vaccination intention change by potential motivators were pooled across 10,008 parents, resulting in 80,064 observations. PRs (95% CIs) were determined using generalized estimating equations for a log-linear Poisson regression model, clustering eight answers within the same parents. The horizontal axis is the log scale. Abbreviations: CI, confidence interval; PR, probability ratio.
Discussion
To the best of our knowledge, this was the first study to examine the potential motivators affecting parental intention in COVID-19 vaccination after approval for children aged 6 months to 4 years in Japan.
Our study had three major findings. First, more than 80% of respondents who were parents of children aged 6 months to 4 years were hesitant to vaccinate their children with COVID-19, which is higher than that of previous studies in other countries and Japan. Studies from the United States and Malaysia that investigated parents of children aged <5 years reported that 60.3%–68.8% of respondents were hesitant about COVID-19 vaccination for their children.Citation23–26 One of the reasons for these differences may be related to the high level of concern about vaccine safety in general among the Japanese.Citation27 Other Japanese studies reported vaccine hesitancy for COVID-19 rates of 35.3% and 57.1% for parents with children aged 3–14 and 0–15 years, respectively.Citation4,Citation5 Those studies were conducted when people were under social restrictions, such as staying home, wearing masks, and social distancing. The desire to return to normal life in these studies might have influenced the differences. Additionally, since prior studies have shown an association between parents of younger children and higher COVID-19 vaccine hesitancy, the focus of the current study on young children under 5 years old may have contributed to the high hesitancy rate.Citation28 This study was conducted during the eighth wave of COVID-19,Citation16 which had the highest recorded number of deaths; however, many of the infected individuals who died of the virus were older adults. Therefore, parents may have thought that the impact on their children would be limited. This fact may also have influenced the high percentage of parental COVID-19 vaccine hesitancy. Second, parents in Groups II (i.e., Inclined not to have my child vaccinated) and I (i.e., Not sure about my child’s COVID-19 vaccination) were around two and three times more likely to be motivated to vaccinate their children by any potential motivators than parents in Group III (i.e., Do not want my child to receive COVID-19 vaccination). In other words, among vaccine hesitators, parents with lower levels of hesitancy were more likely to be motivated to vaccinate their children with the COVID-19 vaccine through potential motivators, which is consistent with a previous study.Citation21 Although this result was expected, it is important as evidence supporting the initial approach of targeting individuals with low levels of hesitancy to improve vaccination rates. Third, vaccine hesitators were motivated to vaccinate their children by proven vaccine effectiveness (protecting children from getting sick [factor 1] and less likely to infect adults [factor 3]), as well as vaccine safety (safe vaccination of millions of children [factor 2]) compared to injunctive norm (recommendation of the public health authority [factor 7] and community leader [factor 8]). A previous systematic review found that confidence in COVID-19 vaccination was a significant predictor of parents’ attitudes toward vaccination, which is consistent with our result.Citation10 These results suggest that when considering vaccination for children, Japanese parents emphasize the evidence of the vaccine’s effectiveness and safety more than the authority’s recommendations. This result also showed that the impact of injunctive norms on vaccine intention change was limited. Some studies exist on the relationship between perceived injunctive norms and COVID-19 vaccine hesitancy for adults;Citation29,Citation30 however, results are inconsistent and not for parents; therefore, this warrants further research.
As implications for policymakers and healthcare providers, given the high hesitancy rate, efficient and effective interventions need to be urgently considered. To reduce parental vaccine hesitancy, giving priority to addressing parents with low levels of hesitancy concerns may be efficient. The result of this study also indicates the importance of communication focusing on the effectiveness and safety of COVID-19 vaccines for Japanese parents. As Katharine et al. highlighted,Citation21 existing messages may not have adequately addressed this concern meaningfully for parents. Thus, developing an effective intervention to focus on parent’s concerns about COVID-19 vaccine efficacy and safety that is consistent with parents’ needs is crucial. This study’s findings provide practical suggestions for intervention planning for COVID-19 vaccine hesitancy in Japan. However, only providing information about vaccine safety and effectiveness to vaccine-hesitant individuals can have the opposite effect.Citation31,Citation32 Therefore, further studies are needed to understand those discrepancies and develop tailored, effective approaches to reduce vaccine hesitancy.
The strength of this study is that it covered the representative of all prefectures in Japan using large-scale data. This study provides vital information to healthcare workers and policymakers in Japan to understand the characteristics of parents who are hesitant about their children’s COVID-19 vaccination. It will also help identify effective approaches to address parent’s concerns and reduce vaccine hesitancy. Nevertheless, this study had some limitations. First, since we used internet-based survey data and non-random sampling, the selection and no-response biases of participants should be considered when interpreting the study results. However, as mentioned above, the distribution of participants by prefecture ensures a certain degree of representativeness for this sample. Second, inappropriate responses may have been obtained by survey respondents not devoting sufficient attention when answering a survey.Citation33 Therefore, to minimize this influence, we excluded individuals who did not correctly answer the simple instructional question and very short-time respondents from the analysis. Third, this was a cross-sectional study; therefore, the parent’s intention was a snapshot in time. However, vaccine intention may change over time; therefore, we should monitor and model the change in future research. Fourth, although our questions measured parental vaccine hesitancy are consistent with the literature, they have not been validated. Since there are various ways to measure parental vaccine intention (e.g., including midpoint response or not), caution should be taken in comparing the hesitancy rate with other studies. Fifth, unmeasured confounding factors may have contributed to the result.
In conclusion, this study found that 80.1% of respondents who were parents of children aged 6 months to 4 years were hesitant to vaccinate their children against COVID-19. Among vaccine hesitators, parents with lower levels of hesitancy were more likely to be motivated to vaccinate their children with the COVID-19 vaccine through potential motivators. Additionally, vaccine-hesitant parents were motivated to vaccinate their children by proven vaccine effectiveness and safety rather than authority’s recommendation. Therefore, the initial approach of targeting parents with low levels of hesitancy is an effective strategy that motivates COVID-19 vaccination. Also, providing evidence-based information about COVID-19 vaccine efficacy and safety that is consistent with parents’ needs is crucial. COVID-19 as a global health emergency has passed, but the wave of infection continues, and socioeconomic activities have returned. Dissemination of the COVID-19 vaccine is more important now to balance infection control and socioeconomic activities. This great hesitancy rate is a future lesson for us. Also, knowledge of the current study which showed parental attitude to the new vaccine, is valuable to counter emerging infectious diseases that may occur in the future.
Author contributions
Conceptualization, Y.K. and S.N.; methodology, All authors; investigation, Y.K.; formal analysis, Y.K.; original draft preparation, Y.K.; review and editing, All authors.; supervision, S.N.; funding acquisition, Y.K. and S.N. All authors have read and agreed to the published version of the manuscript.
Supplementary_material_YK_clean.docx
Download MS Word (442.6 KB)Acknowledgments
We thank all respondents of this study. Sincere appreciation is extended to the advice and expertise of Shinya Masuda, Ph.D, Aaron Olaf Batty, Ph.D and Ardith Z. Doorenbos, PhD, RN, FAAN.
Disclosure statement
No potential conflict of interest was reported by the author(s).
Data availability statement
Raw data were generated at Keio University. Derived data supporting the findings of this study are available from the corresponding author Y.K. on reasonable request.
Supplementary material
Supplemental data for this article can be accessed on the publisher’s website at https://doi.org/10.1080/21645515.2023.2296737.
Additional information
Funding
References
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