Impact of Vaccination on Rotavirus Genotype Diversity: A Nearly Two-Decade-Long Epidemiological Study before and after Rotavirus Vaccine Introduction in Sicily, Italy.

Sicily was the first Italian region to introduce rotavirus (RV) vaccination with the monovalent G1P[8] vaccine Rotarix® in May 2012. In this study, the seasonal distribution and molecular characterization of RV strains detected over 19 years were compared to understand the effect of Rotarix® on the evolutionary dynamics of human RVs. A total of 7846 stool samples collected from children < 5 years of age, hospitalized with acute gastroenteritis, were tested for RV detection and genotyping. Since 2013, vaccine coverage has progressively increased, while the RV prevalence decreased from 36.1% to 13.3% with a loss of seasonality. The local distribution of RV genotypes changed over the time possibly due to vaccine introduction, with a drastic reduction in G1P[8] strains replaced by common and novel emerging RV strains, such as equine-like G3P[8] in the 2018−2019 season. Comparison of VP7 and VP4 amino acid (aa) sequences with the cognate genes of Rotarix® and RotaTeq® vaccine strains showed specific aa changes in the antigenic epitopes of VP7 and of the VP8* portion of VP4 of the Italian RV strains. Molecular epidemiological surveillance data are required to monitor the emergence of novel RV strains and ascertain if these strains may affect the efficacy of RV vaccines.