Emergence of GII.4 Sydney[P16]-like Norovirus-Associated Gastroenteritis, China, 2020-2022.

Newly evolved GII.4 Sydney[P16] norovirus with multiple residue mutations, already circulating in parts of China, became predominant and caused an abrupt increase in diagnosed norovirus cases among children with gastroenteritis in Shanghai during 2021-2022. Findings highlight the need for continuous long-term monitoring for GII.4 Sydney[P16] and emergent GII.4 norovirus variants.