Changes in vaccine coverage and incidence of acute gastroenteritis and severe rotavirus gastroenteritis in children <5 years in Shibata City, Niigata Prefecture, Japan.

Rotavirus (RV) vaccines were first introduced in 2011 and adopted for universal vaccination in 2020 in Japan. However, the effectiveness of RV vaccines after being adopted for universal vaccination in 2020 has not been reported. Because of the easy accessibility of clinics in Japan, many children are not usually hospitalized for RV gastroenteritis (RVGE). Therefore, in order to evaluate the impact of the RV vaccine since 2008, we investigated the incidence of hospitalization for RVGE as well as the frequency of children aged < 5 years who received medical treatment for severe RVGE at clinics in Shibata City, Japan. The RV vaccine coverage rate was 94.0% (1,046/1,113) in Shibata City after universal vaccination in 2020; this was a significant increase from previous rates. The incidence per 1000 person - years for RVGE hospitalization and severe RVGE at clinics were significantly higher among children aged < 3 years than in previous time periods. The incidence in children with all acute gastroenteritis (AGE) decreased significantly after universal vaccination during the COVID-19 pandemic. The proportion of severe RVGE among all AGE cases also decreased significantly after universal vaccination among children aged < 3 years (0.0%) and those aged 3-4 years (0.6%). There were significant differences in the distribution of RV genotypes isolated from the feces of children with RVGE between different eras divided by RV vaccination rates, especially G1P[8], which was the major genotype before it recently almost disappeared. Further studies are warranted to assess the impact of the COVID-19 pandemic.