Rotavirus epidemiology 5-6 years after universal rotavirus vaccination: persistent rotavirus activity in older children and elderly.

Background: Rotavirus (RV) vaccination using RotaTeq vaccine exclusively was introduced into Finnish National Immunization Program (NIP) in 2009, and soon reached high (≥90%) coverage. Since mid-2013, all stool samples from laboratory diagnosed cases of RV gastroenteritis in the entire country have been typed.

Methods: 364 RV positive stool samples collected from clinical laboratories over a 2-year period were G- and P-typed using RT-PCR, and the results were confirmed by sequencing. In addition, the genome segment encoding for VP6 was sequenced to distinguish between wild-type and vaccine origin (bovine) RVs.

Results: RV winter epidemic seasons 2013-2014 and 2014-2015 lasted until July each. The age distribution of RV cases showed two unusual clusters: one in children 6-16 years of age, too old to have been vaccinated in NIP, and the other in elderly over 70 years of age. In children, diverse genotypes were observed without any obvious predominance. The most common ones were G1P[8] (30.0%), G2P[4] (22.4%), G9P[8] (15.8%), G3P[8] (12.2%) and G4P[8] (11.2%). The genotype distribution was not different among vaccinated and unvaccinated children. Most cases in the elderly were associated with G2P[4].

Conclusions: Even at high vaccine coverage and high effectiveness of RV vaccine, RV activity continues to persist, particularly in unvaccinated older children. RV genotypes show greater diversity than before RV vaccinations. We conclude that RV disease can be controlled but not eliminated by vaccinations. Herd-protection in long-term follow-up may be less than at the start of RV vaccinations.