Rotavirus vaccine effectiveness against the risk of hospitalization and the impact of public expense for the vaccine on a regional rotavirus gastroenteritis epidemic in Japan

An epidemic of rotavirus (RV) gastroenteritis occurred from April to July 2015 across a wide area of Hokkaido, surrounding the Abashiri-Kosei General Hospital. The RV vaccine for children in Shari and Koshimizu was provided at public funds by their local governments, while children in Abashiri were charged for the vaccine. This study examined the effectiveness of the RV vaccine against the risk of hospitalization based on a retrospective cohort study and the impact of using public funds for RV vaccination on a regional RV gastroenteritis epidemic. The vaccination coverage was significantly higher in children in Shari and Koshimizu than in Abashiri (87.8% vs. 42.7%, respectively, p < 0.001). The RV gastroenteritis-related risk of hospitalization was slightly lower in children from Shari and Koshimizu than in those from Abashiri (1.6% vs. 3.2%, respectively, p = 0.07). In addition, the risk of hospitalization in the vaccinated children was significantly lower than that in the unvaccinated children (0.7% vs. 4.8%, respectively, p < 0.001); indicating that the RV vaccine effectiveness against the risk of hospitalization was 96.5% (95% confidence interval 45.7%-99.8%). In conclusion, the use of public funds for the provision of RV vaccine increased the vaccination coverage, which, in combination with high vaccine effectiveness, led to a decrease in the number of hospitalizations in children during a regional RV gastroenteritis epidemic.