First year experience of rotavirus immunisation programme in Finland.

Introduction: This study aimed to estimate the impact of rotavirus (RV) immunisation programme on the total hospital treated acute gastroenteritis (AGE) burden, as well as, on severe RV disease burden in Finland during the first year after immunisation programme introduction. Such studies can also be considered as a vaccine-probe-study, where unspecific disease burden prevented by immunisation is assumed to be caused by the agent the vaccine is targeted against.

Methods: The RV related outcome definitions were based on data registered in the National Hospital Discharge Register coded using ICD 10 codes. Incidences of hospitalised and hospital outpatient cases of AGE and RVGE were compared prior (1999-2005) and after (2010) the start of the programme among children under 5 years of age. ICD 10 codes utilised were A00-A09, R11 and K52.

Results: The reductions in disease burden, when the post-introduction year was compared to pre-vaccine era, were 80.3% (95% CI 74.5-84.7) in hospital inpatient RVGE among toddlers less than 1 year of age and 53.9% (95% CI 49.8-57.7) when the total inpatient AGE burden was considered in the same age group. For the corresponding hospital outpatient cases the reductions were 78.8% (95% CI 48.4-91.3) and 12.5% (7.1-17.7). The overall vaccine impact against confirmed RVGE in age cohorts eligible for vaccination before the RV season 2010 was 97% (95% CI 90.7-99.0). If the total reductions, both in diagnosed RVGE, as well as in cases without definite microbial diagnosis, were expected to be RVGE, population based estimates for the total disease burden can be obtained: for inpatient RVGE in children less than 1 year of age the estimate is 10.5/1000 pyrs, while the diagnosed specific incidence was less than half of that, 4.9/1000 pyrs.

Discussion: During the first post-vaccination year 2010, RV immunisation programme clearly managed to control the severe, hospital treated, forms of RVGE. The total disease burden is a more valuable end point than mere diagnosed cases as laboratory confirmation practises change after vaccine introduction. Our study is limited by the very short post-introduction follow up.