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

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.

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.

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.

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.