Changes in the mumps vaccine coverage and incidence of mumps before and after the public subsidization program: A descriptive study using a population-based database in Japan.

BACKGROUND Evidence suggests that mumps infection can be eradicated by continuous mumps vaccine coverage. However, due to safety concerns, the mumps vaccination program in Japan shifted from routine to voluntary. To improve vaccination coverage rates, some municipalities began to independently provide subsidization programs for the mumps vaccine. However, the changes in vaccination coverage and incidence of mumps before and after initiating the subsidization programs remain unknown. METHODS In April 2018, a city in Japan started a subsidization program for the mumps vaccine for children aged 1-6 years. This study used data on vaccination records and healthcare claims from the city obtained between July 2016 and December 2019. We described changes in vaccination coverage, and the incidence of mumps infections before and after the start of the subsidization program. RESULTS The mumps vaccination coverage rate among eligible children was 3.3% at the program's initiation; this increased by about 1.5% per month, reaching 38.4% 21 months after the initiation of the program. Among 308,976 individuals, 145 cases of mumps were identified; of these, 92 cases (0.27 cases per 1,000 person-years) occurred before, and 53 (0.15 cases per 1,000 person-years) occurred after the initiation of the subsidization program. CONCLUSION While the mumps vaccination coverage rate increased after the initiation of the subsidization program, it did not reach the level required for eradication.