The COVID-19 pandemic highlighted the tension between individual autonomy and collective well-being in public health. While vaccination offers individual health benefits and contributes to herd immunity, promoting vaccination requires addressing the conflict between self-interest and collective interest. Existing research suggests a direct link between these interests and vaccination intentions, with collective interest positively correlating with vaccine uptake. However, the role of institutional trust and gender remains under-explored. This study, grounded in expectancy-value theory (EVT) and the selectivity hypothesis, investigates the effects of self-interest and collective interest on attitudes toward vaccination in Israel, a context with strong government-led vaccination campaigns. It examines the mediating role of institutional trust and the moderating role of gender in this relationship. Understanding these factors is crucial for designing effective public health policies and communication strategies that resonate with individual values while achieving societal health goals.

Expectancy-value theory (EVT) posits that behavior is driven by expected outcomes and their perceived value. In the vaccination context, collective interest (altruism) is expected to positively influence vaccination attitudes, while self-interest (egoism) is expected to negatively influence them. Previous research supports this, showing a correlation between prosocial behavior and vaccine acceptance. Institutional trust, often defined as confidence in institutions' trustworthiness, has also been identified as a significant predictor of vaccination intentions. However, the literature lacks a comprehensive investigation into the interplay between self-interest, collective interest, institutional trust, and gender in shaping vaccination attitudes. The selectivity hypothesis suggests that women process information more comprehensively than men, which might affect their reliance on institutional trust when making decisions about vaccination.

Data were collected through an online survey using Blueberries, an online access panel survey company, among 464 Israeli adults aged 18-57. The sample comprised 56% females and 44% males. The survey included validated scales measuring attitudes toward vaccination, institutional trust, collective interest, and self-interest, using 7-point Likert scales. Confirmatory factor analysis (CFA) assessed the construct validity and reliability of the measures. Moderated mediation analysis (PROCESS MODEL 14) with 20,000 bootstrapped samples was employed to test the hypotheses. This involved two separate models: one examining the relationship between collective interest and vaccination attitudes, and the other examining the relationship between self-interest and vaccination attitudes. In each model, institutional trust was treated as a mediator and gender as a moderator.

The CFA confirmed the validity and reliability of the measures. The results supported all hypotheses. First, collective interest showed a positive direct effect on attitudes toward vaccination. Second, self-interest showed a negative direct effect on vaccination attitudes. Third, institutional trust mediated the relationship between both collective interest and self-interest, and attitudes toward vaccination. Fourth, gender moderated the mediating effect of institutional trust: the mediating effect of institutional trust was stronger for females than for males in both collective and self-interest models. Specifically, for the collective interest model, the direct effect was positive (B=0.15, p<0.05), the indirect effect through institutional trust was positive, with a stronger effect observed among females (B = 0.49, p < 0.01) compared to males (B=0.27, p<0.01). The interaction effect between institutional trust and gender was also positive and significant (B=0.22, p<0.05). For the self-interest model, the direct effect was negative (B=-0.15, p<0.01), the indirect effect through institutional trust was positive and stronger among females (B=0.49, p<0.01) than males (B=0.27, p<0.01), and the interaction effect between institutional trust and gender was positive and significant (B=0.22, p<0.05).

The findings support the existence of two distinct pathways to vaccine acceptance. For those driven by collective interest, positive attitudes are directly influenced by altruistic motivations and indirectly enhanced through institutional trust, with a stronger effect observed among females. For individuals driven by self-interest, negative attitudes are directly expressed but can be counteracted by the indirect positive influence of institutional trust, particularly among females. These results highlight the importance of institutional trust in shaping vaccine attitudes, regardless of underlying individual motivators. The stronger influence of trust on females might be explained by the selectivity hypothesis, where women's more comprehensive information processing leads to stronger trust development and greater impact on vaccine acceptance. The study shows that intrinsic motivations (self/collective interest) are complemented by extrinsic motivations (institutional trust) in predicting vaccine attitudes.

This study contributes to the understanding of vaccine acceptance by demonstrating the interplay between self-interest, collective interest, institutional trust, and gender. It shows that institutional trust can significantly influence attitudes toward vaccination, particularly among women, regardless of underlying individual motivations. Policymakers should focus on strengthening institutional trust and tailoring communication strategies to different genders, recognizing their distinct information processing styles. Future research could explore these relationships across different vaccines and populations and investigate other demographic factors influencing this complex interplay.

The study's cross-sectional design limits causal inference. The focus on the Israeli context during the COVID-19 pandemic may limit the generalizability of findings to other settings or different vaccines. The age range of participants (18-57) also limits the scope of the study. Future research should investigate these relationships in longitudinal studies, diverse contexts, and across a broader age spectrum, incorporating other potentially relevant variables such as education and ethnicity.