Success of rotavirus vaccination in Finland, a register based study measuring impact beyond overall effectiveness

Abstract Introduction Even with vaccines available since 2006, rotavirus continues to be a major cause of acute gastroenteritis globally in children under 5 years old. Finland introduced the rotavirus vaccine to its national vaccination programme in 2009. Since then hospitalizations due to gastroenteritis caused by rotavirus (RVGE) and of all causes (AGE) have been reduced significantly in young children. Methods We performed a retrospective analysis of data from register databases consisting of over 200 000 children aged 0.5-2 years. Children born before rotavirus vaccines were available (2002, 2003) and after the implementation of rotavirus vaccination programme (2014, 2015) were followed for episodes of acute infectious gastroenteritis. We calculated the incidences of hospital outpatient and inpatient episodes and used individual vaccination records to estimate the overall, total, direct and indirect vaccine effect (VE %). Results Among children born in 2014 and 2015, there was a 96% reduction in inpatient RVGE episodes and a 78% reduction in episodes of inpatient AGE compared to the pre-vaccination era, comprising the overall VE. Direct effectiveness was 96% and 53% for RVGE and AGE respectively. Herd effect i.e. indirect protection was estimated to be 67% against inpatient RVGE and 56% against inpatient AGE. Protection acquired by the vaccinated children when compared to pre vaccination era i.e. the total VE was 99% for inpatient RVGE and 79% for inpatient AGE. Conclusions Although overall incidences for every disease type studied were reduced, rotavirus is still circulating with seasonality and there is a slight shift of disease towards the older age groups. Together with changes observed in the distribution of rotavirus genotypes, our results indicate that continuous monitoring is still necessary.