Trends in voluntary vaccination coverage in a Japanese city.

BACKGROUND: Large numbers of patients with diseases preventable by voluntary vaccines have been reported in Japan. However, it is difficult to analyze the impact of voluntary vaccination on disease prevention, as governments do not aggregate the number of recipients of vaccines that are not included in the national immunization program. This study investigated the association between the coverage rates of two voluntary vaccines (rotavirus and mumps vaccines) and the incidence of the diseases preventable by these vaccines. METHODS: We performed a prospective questionnaire-based observational study to investigate the presumptive coverage rates of the rotavirus vaccine in infancy and the mumps vaccine at 1 year of age in Kitakyushu City from 2015 to 2018. The number of children admitted to a secondary medical institution for rotavirus-associated gastroenteritis and the incidence of mumps infection in sentinel medical institutions were also analyzed during the investigation period. RESULTS: The rotavirus and mumps vaccine coverage rates since 2016 were 61-63% and late 28-30%, respectively (52.6% and 20.3% in 2015, respectively). The yearly number of children hospitalized for rotavirus-associated gastroenteritis from 2015 to 2018 declined by 41.4% compared with that during the pre-vaccination period (2009-2011). The incidence of mumps infection remained unchanged during the investigation period. CONCLUSION: The coverage rates of two voluntary vaccines were not high enough to control the infections. The incorporation of voluntary vaccines into the routine immunization program should be considered as the one of the effective ways to increase vaccination coverage.