Rotavirus (RV) vaccination has been available in Japan since November 2011, but is not yet part of Japan's national immunisation programs. There are insufficient data on vaccine effectiveness (VE) among Japanese children.
Between the months of January and May in 2014 and 2015, we conducted active surveillance of gastroenteritis among children at 14 medical facilities. Rectal swabs from all patients with diarrhoea or vomiting were tested for RV by immunochromatography, and positive specimens were genotyped. Demographic data and immunisation records were obtained from a questionnaire completed by their parents/guardians or medical records. A test-negative case-control design was used to examine vaccine effectiveness (VE) using unconditional logistic regression analysis adjusted for possible confounding factors.
Among the 1519 eligible subjects (children with acute gastroenteritis symptoms aged ≥2 months to <3 y visiting medical facilities) recruited, 487 cases and 925 controls were enrolled. Cases had more severe symptoms than controls, requiring more intensive treatment, including intravenous rehydration or hospitalisation. VE against all rotavirus gastroenteritis (RVGE) was 80.0% (95% confidence interval [CI], 72.8-85.5%), and VEs against RV1 and RV5 were similar, at 80.6% (95%CI, 70.7-87.1%) for RV1 and 80.4% (95% CI, 69.1-87.6%) for RV5. Although VEs of both vaccines decreased with age, VEs against all RVGE were >70% up to 2 years after vaccination. VEs increased with severity of RVGE, and VE against severe RVGE, requiring intravenous rehydration or hospitalisation, was 97.3% (95% CI, 88.8-99.3%). VEs of RV1 and RV5 against G1P and G2P were comparable, at RV1, 89.8% (95% CI, 78.2-95.5%) and 78.3% (95% CI, 23.6-93.8%); and RV5, 85.8% (95% CI, 72.8-92.6%) and 88.1% (95% CI, 10.1-98.4%), respectively.
Rotavirus vaccines were effective in preventing mild to severe RVGE, irrespective of vaccine type, time since vaccination, or RV genotype.