Abstract
INTRODUCTION: Japan introduced a routine rotavirus vaccination programme in October 2020, and infants born in or after August 2020 were eligible to be vaccinated under full government subsidy. However, the effects of this programme on vaccination coverage and vaccination factors remain unclear. This study aimed to determine the changes in rotavirus vaccination coverage and factors among infants residing in a Japanese municipality before and after the introduction of routine rotavirus vaccinations. METHODS: This retrospective cohort study was conducted using vaccination records, resident register data and medical claims data acquired from a municipality. We identified infants born between April 2019 and February 2022; infants born before August 2020 were analysed as 'pre-introduction', and infants born in or after August 2020 were analysed as 'post-introduction'. The pre-post changes in vaccination coverage were examined using an interrupted time-series analysis. To identify vaccination factors, we analysed the associations of sociodemographic and socioeconomic factors with rotavirus vaccination status using Poisson regression and modified least-squares regression analyses. The risk ratios and risk differences were estimated. RESULTS: We analysed 26 174 infants (pre-introduction: 12 532, post-introduction: 13 642). The introduction of routine rotavirus vaccinations was immediately followed by an increase of 11.24% in vaccination coverage. These increases were notable among infants with ≥3 siblings (40.47%) and infants covered by public assistance (60.65%). Next, infants with older siblings, younger mothers, single-mother households and use of public assistance were less likely to be vaccinated in the pre-introduction period. The post-introduction period showed generally similar trends in vaccination factors. However, the introduction of routine rotavirus vaccinations substantially reduced the impact of these factors on vaccination status. CONCLUSIONS: The introduction of the routine rotavirus vaccination programme improved vaccination coverage and reduced the impact of sociodemographic and socioeconomic factors on vaccine uptake.