Vaccination recommendations to others among physicians and the general public: effects of birth-year-based vaccination policy changes assessed by regression discontinuity analysis

Introduction: Recommendations from physicians and peers play a crucial role in promoting vaccination. This study evaluated differences in recommendations to others regarding four vaccines with varying efficacy (seasonal influenza, measles, human papillomavirus [HPV], and coronavirus disease 2019 [COVID-19]) between physicians and the general public and examined the impact of birth-year-based vaccination policy changes on these recommendations. Methods: This cross-sectional study was conducted in February 2026 among 492 physicians and 5,252 members of the general public in Japan. Consistency in recommendations across the four vaccines was assessed using the intraclass correlation coefficient (ICC[3,1]), and group differences were examined using a two-way mixed-design analysis of covariance. Multilevel regression discontinuity analyses were performed to evaluate the effects of birth-year-based vaccination policy. Results: Physicians showed significantly stronger recommendations to others than the general public, and their recommendation patterns generally reflected vaccine efficacy. However, physicians showed lower consistency across vaccine types than the general public (ICC[3,1]), driven primarily by heterogeneity in COVID-19 vaccine recommendations. Regression discontinuity analyses showed that birth-year-based vaccination policy, including routine vaccination opportunities, was significantly associated with recommendations to others for measles and HPV vaccines, independently of perceived benefits and risks. Conclusion: To improve vaccination coverage from a public health perspective, it is important for physicians to provide effective vaccination recommendations to the general public on a broader scale; however, it is also necessary to address the heterogeneity in vaccine-specific recommendation patterns among physicians, as observed for COVID-19. Routine vaccination opportunities may increase vaccination coverage not only through the routine vaccination program itself but also through peer effects among the general public. Vaccination policy may therefore influence vaccination coverage not only in the current generation but also in future generations. Designing vaccination policy should consider its long-term impact on future vaccination coverage as well as herd immunity.