Understanding COVID-19 Vaccination Intention in Japan: The Influence of Individual Social Capital and Personal Beliefs on Vaccination.

Background/Objectives: Vaccine hesitancy remains a significant public health challenge in Japan, particularly following the HPV vaccine suspension (2013-2022) that severely damaged vaccination trust. Although prior studies have linked individual social capital to vaccination behavior in Japan, whether and how personal vaccination beliefs modify this association remains poorly understood. This study examined associations between individual social capital (resources accessed through personal social networks) and COVID-19 vaccination intention, and how these associations interact with personal vaccination beliefs based on the 7C model. Methods: A nationwide web-based survey (January 2024) included 7210 participants aged 20-69. Individual social capital was measured using civic participation, social cohesion (community trust), and reciprocity (mutual helping). Personal beliefs were assessed via the 7C model (psychological vaccination determinants framework) and factor-analyzed. Logistic regression examined associations; interaction analyses tested whether social capital effects differed across belief patterns. Results: Overall, 73.1% expressed intention to receive COVID-19 vaccination for 2024-2025. All social capital components positively associated with vaccination intention: social cohesion (adjusted OR = 1.80, 95% CI:1.58-2.04), reciprocity (adjusted OR = 1.64, 95% CI:1.33-2.02), and civic participation (adjusted OR = 1.29, 95% CI:1.10-1.51). Factor analysis identified three belief domains: individual and collective health responsibility, trust in vaccination systems, and safety concerns. Health responsibility beliefs substantially reduced social capital-vaccination associations when included in models. Safety concerns moderated effects of social cohesion (p < 0.001) and reciprocity (p = 0.011), with stronger effects among those with lower concerns. Civic participation was associated with vaccination intention mainly among those with higher institutional trust. Conclusions: Individual social capital was significantly associated with vaccination intention through complex belief interactions. Safety concerns act as crucial moderators. Multifaceted strategies addressing social capital, safety concerns, and institutional trust may be needed to increase vaccine uptake.