Appearance and spread of norovirus genotype GII.17 subcluster C2 (Romania-2021 like) in Nizhny Novgorod, Russia, 2021–2023

Noroviruses are one of the leading causes of acute gastroenteritis worldwide and have significant genetic diversity. In this study, based on phylogenetic analysis of genome sequences of noroviruses circulating in Nizhny Novgorod in 2014–2023 and previously published sequences obtained from the GenBank database, we show a return to active circulation of cluster C of genotype GII.17[P17], which was displaced in 2015–2016 by cluster D. A new subcluster, C2 (Romania-2021 like), was identified and found to be different from subcluster C1 (Kawasaki-2014), which circulated in the middle of the last decade. Amino acid substitutions characteristic of C2 were found in the main structural protein VP1, bringing it closer to the Tokyo_JP_1976 strain identified in the 1970s. It was established that representatives of the C2 subcluster (Romania-2021 like) circulated in 2021–2023 in European and American countries and caused outbreaks of norovirus infection. The data obtained indicate that the evolution of the phylogenetic lineage represented by cluster C of the GII.17 genotype continued in the last decade and had the character of a return to the ancestral strain. Moreover, these processes were not detected for four years (2017–2020).