Shortage of Japanese encephalitis vaccine and vaccination coverage in three municipalities in Japan: the VENUS study.

Objectives: To describe routine Japanese encephalitis (JE) vaccination coverage patterns among priority and nonpriority groups during the 2021 JE vaccine shortage and prioritization policy in Japan, and after supply restoration. Methods: Using vaccination and resident registry data from three municipalities in the Vaccine Effectiveness, Networking, and Universal Safety (VENUS) Study, we assessed cumulative vaccination coverage at each fiscal year (FY)-end in nine Phase 1 birth cohorts and nine Phase 2 annual cohorts (April 2014-March 2023) using descriptive analyses. Results: Among 60,122 children in Phase 1 and 74,914 in Phase 2, first- and second-dose coverage in the prioritized FY 2018 birth cohort was 62.0% and 50.5%, respectively, at age 3 years. Third-dose coverage at age 4 years declined to 6.9% in the FY 2017 birth cohort, compared with 37.5% to 41.4% in prior cohorts, and increased to 49.9% by age 5 years. Fourth-dose coverage at age 9 years was 1.3% in the FY 2012 birth cohort and increased to 32.7% by age 10 years. Conclusion: The JE vaccine shortage temporarily reduced coverage among nonpriority groups, whereas coverage was maintained among prioritized children in 3 Japanese municipalities. Age- and dose-specific monitoring could identify deferred cohorts and support targeted follow-up measures in case of vaccine supply disruptions.