Emerging norovirus GII.4 Sydney[P31] causing acute gastroenteritis outbreak in children in Japan, during COVID-19, 2021

Prevalence of Human Norovirus GII.4 Sydney 2012 [P31] between 2019 and 2021 among Young Children from Rural Communities in South Africa

“…However, in some cases, norovirus strains were closely related to other circulating strains outside of Africa, which is thought to have been due to population movement prior to the COVID-19 pandemic lockdown. Sequence analysis showed that GII.4 Sydney 2012 strains ( Figure 2 and Figure 3 ) are most phylogenetically related to the HNoV strains recently reported in Japan [ 60 ] in sporadic cases and outbreaks and elsewhere in countries such as China [ 74 ], Botswana [ 75 ], and Ghana [ 10 ]. The GII.4 variants became predominant in outbreaks starting from the early 1990s until the current circulating GII.4 Sydney 2012.…”

“…It is unclear what may have selectively facilitated the epidemiological fitness and spread of the HNoV GII.4 Sydney 2012 P31 strain amid COVID-19 in the study area. However, the same strain was reported to be circulating in Japan and China during COVID-19 [ 22 , 60 ]. The features of epidemiological fitness are not easily quantifiable [ 24 ].…”

“…Data indicating both the rise and decline in norovirus cases during the COVID-19 pandemic were reported [ 58 , 59 ]. Furthermore, norovirus outbreaks occurred during the COVID-19 pandemic in China and Japan [ 22 , 60 ].…”

“…We observed less than 50% similarity in the nucleotide sequences of HNoV GII.4 strains obtained in this study compared to previously published data ( Data S1 ). The genetic variation of HNoV strains over the years ascertains how HNoV may continue to affect vulnerable communities in different countries, with the possibility of the emergence of new variants in the near future [ 22 , 60 ]. The variation of sequence nucleotides could explain the viral adaptability and epidemiological fitness or dominance in the area [ 72 ].…”