Clinical, Molecular and Evolutionary Characterization of Noroviruses in Hospitalized Children With Acute Gastroenteritis in Vietnam, 2016 to 2021.

Following rotavirus vaccine implementation in Vietnam, norovirus has gradually become equally an important as a cause of acute gastroenteritis (AGE) in children as rotavirus. This study aimed to investigate the genotype distribution and compare clinical manifestations of norovirus of children < 5 years of age hospitalized with AGE from 2016 to 2021. Of 6,718 specimens collected through active surveillance from 12/2016 to 05/2021, 2,317 (34.5%) were randomly selected for norovirus testing. Among the 477 (20.6%) norovirus-positive specimens identified from the previous surveillance, 390 (81.8%) were successfully genotyped for both partial RdRp and VP1 genes using online typing tools and 47 were selected for whole-genome sequencing. Overall, norovirus genogroup-II (GII) viruses dominated (97.3%) followed by GI (2.5%) and dual GI/GII infections (0.2%), with GII.4Sydney[P16] as the predominant genotype (51.5%) followed by GII.3[P12] (23.9%). Children infected with GII.4Sydney more commonly presented with thirst (65.8% vs 53.7%, p < 0.05) and showed a trend toward higher rates of sunken eyes compared with other genotypes (48.1% vs 38.1%, p = 0.053). A shift in predominant strain from GII.4Sydney[P31] viruses (50.8%) in 2016-2017 to GII.4-Sydney[P16] (51.9%-68.9% in 2018-2021) was observed. Two cases in 2017 were typed as GII.4Hong Kong[P31]. Compared to GII.4 Sydney[P31], GII.4Hong Kong had 12 amino acid substitutions in the P1-P2 domains. This study highlights the evolving genetic diversity of norovirus genotypes in Vietnam. The shift of the predominant strain from GII.4Sydney[P31] to GII.4Sydney[P16] in 2018 and detection of GII.4 Hong Kong[P31] in 2017 emphasizes the need for continuous molecular surveillance to inform public health prevention strategies.