Long-term surveillance of rotavirus vaccination after implementation of a national immunization program in Finland (2008-2018)

BACKGROUND: Rotavirus (RV) vaccination was included in the Finnish National immunization Program (NIP) in 2009. RotaTeq (RV5) has been used exclusively with a national average vaccination coverage rate (VCR) of > 90%. While previous studies have demonstrated that inpatient rotavirus gastroenteritis (RVGE) admissions declined by as much as 96% in Finnish children ≤ 5 years old following RV vaccination introduction, no study has evaluated long-term protection after vaccination in Finland. In this study, we analyze incidence of hospital outpatient visits and inpatient admissions of gastroenteritis in children up to 7 years of age.

METHODS: We first describe the incidence of RVGE, viral gastroenteritis (VGE), and acute gastroenteritis (AGE) for all Finnish children born during 2008-2011. Children were stratified by the year of birth into not-eligible, partially eligible and rotavirus vaccine-eligible (born in 2008, 2009, 2010 and 2011, respectively). Hospital inpatient and outpatient data was collected from the National Care Register for all children from birth until December 31st, 2018. We also studied RVGE incidence during 2014-2017 for children<3 years of age in municipalities with VCRs of 90% and above and municipalities with VCRs below 90%.

RESULTS: RVGE incidence decreased significantly soon after implementation of RV vaccination in the NIP. In vaccine-eligible cohorts, no clear peak incidence in the youngest age groups could be observed, and no RVGE cases were observed beyond 6 years after vaccination, in contrast to vaccine ineligible and partially eligible cohorts. Despite an overall high VCR in Finland, regions with high VCR had lower incidence of RVGE than regions with lower VCR.

CONCLUSION: Incidence of RVGE has remained low in all age groups during the 10 years following introduction of RV vaccine in the Finnish NIP. Differences in RVGE incidence were observed in regions with high as compared with lower VCR, highlighting the importance of maintaining high vaccination coverage.