Influence of herd immunity on norovirus: a long-term field study of repeated viral gastroenteritis outbreaks at the same facilities

Epidemiological Features of Human Norovirus Genotypes before and after COVID-19 Countermeasures in Osaka, Japan

We investigated the molecular epidemiology of human norovirus (HuNoV) in all age groups using samples from April 2019 to March 2023, before and after the COVID-19 countermeasures were implemented. GII.2[P16] and GII.4[P31], the prevalent strains in Japan before COVID-19 countermeasures, remained prevalent during the COVID-19 pandemic, except from April to November 2020; in 2021, the prevalence of GII.2[P16] increased among children. Furthermore, there was an increase in the prevalence of GII.4[P16] after December 2022. Phylogenetic analysis of GII.P31 RdRp showed that some strains detected in 2022 belonged to a different cluster of other strains obtained during the present study period, suggesting that HuNoV strains will evolve differently even if they have the same type of RdRp. An analysis of the amino acid sequence of VP1 showed that some antigenic sites of GII.4[P16] were different from those of GII.4[P31]. The present study showed high infectivity of HuNoV despite the COVID-19 countermeasures and revealed changes in the prevalent genotypes and mutations of each genotype. In the future, we will investigate whether GII.4[P16] becomes more prevalent, providing new insights by comparing the new data with those analyzed in the present study.

Impact of the COVID-19 pandemic on norovirus circulation in Germany

Human norovirus is a major cause of viral gastroenteritis in all age groups. The virus is constantly and rapidly changing, allowing mutations and recombination events to create great diversity of circulating viruses. With the start of the COVID-19 pandemic in 2020, a wide range of public health measures were introduced worldwide to control human-to-human transmission of SARS-CoV-2. In Germany, control measures such as distance rules, contact restrictions, personal protection equipment as well as intensive hand hygiene were introduced. To better understand the effect of the measures to control the COVID-19 pandemic on incidence and the molecular epidemiological dynamics of norovirus outbreaks in Germany, we analyzed national notification data between July 2017 and December 2022 and characterized norovirus sequences circulating between January 2018 and December 2022. Compared to a reference period before the pandemic, the incidence of notified norovirus gastroenteritis decreased by 89.7% to 9.6 per 100,000 during the 2020/2021 norovirus season, corresponding to an incidence rate ratio (IRR) of 0.10. Samples from 539 outbreaks were genotyped in two regions of the viral genome from pre-pandemic (January 2018 to February 2020) and samples from 208 outbreaks during pandemic time period (March 2020 to December 2022). As expected, norovirus outbreaks were mainly found in child care facilities and nursing homes. In total, 36 genotypes were detected in the study period. A high proportion of recombinant strains (86%) was found in patients, the proportion of detected recombinant viruses did not vary between the pre-pandemic and pandemic phase. The proportion of the predominant recombinant strain GII.4 Sydney[P16] was unchanged before pandemic and during pandemic at 37.5%. The diversity of most common genotypes in nursing homes and child care facilities showed a different proportion of genotypes causing outbreaks. In nursing homes as well as in child care facilities GII.4 Sydney[P16] was predominant during the whole study period. Compared to the nursing homes, a greater variety of genotypes at the expense of GII.4 Sydney[P16] was detected in child care facilities. Furthermore, the overall proportion of recombinant strain GII.3[P12] increased during the pandemic, due to outbreaks in child care facilities. The COVID-19 pandemic had a high impact on the occurrence of sporadic cases and norovirus outbreaks in Germany, leading to a near suppression of the typical norovirus winter season following the start of the pandemic. The number of norovirus-associated outbreak samples sent to the Consultant Laboratory dropped by 63% during the pandemic. We could not identify a clear influence on circulating norovirus genotypes. The dominance of GII.4 Sydney recombinant strains was independent from the pandemic. Further studies are needed to follow up on the diversity of less predominant genotypes to see if the pandemic could have acted as a bottleneck to the spread of previously minoritized genotypes like GII.3[P12].

A non-human primate model for human norovirus infection

Norovirus infection can cause gastrointestinal disease in humans. Development of therapies and vaccines against norovirus have been limited by the lack of a suitable and reliable animal model. Here we established rhesus macaques as an animal model for human norovirus infection. We show that rhesus macaques are susceptible to oral infection with human noroviruses from two different genogroups. Variation in duration of virus shedding (days to weeks) between animals, evolution of the virus over the time of infection, induction of virus-specific adaptive immune responses, susceptibility to reinfection and preferential replication of norovirus in the jejunum of rhesus macaques was similar to infection reported in humans. We found minor pathological signs and changes in epithelial cell surface glycosylation patterns in the small intestine during infection. Detection of viral protein and RNA in intestinal biopsies confirmed the presence of the virus in chromogranin A-expressing epithelial cells, as it does in humans. Thus, rhesus macaques are a promising non-human primate model to evaluate vaccines and therapeutics against norovirus disease.

The impact of anthropogenic climate change on pediatric viral diseases

The adverse effects of climate change on human health are unfolding in real time. Environmental fragmentation is amplifying spillover of viruses from wildlife to humans. Increasing temperatures are expanding mosquito and tick habitats, introducing vector-borne viruses into immunologically susceptible populations. More frequent flooding is spreading water-borne viral pathogens, while prolonged droughts reduce regional capacity to prevent and respond to disease outbreaks with adequate water, sanitation, and hygiene resources. Worsening air quality and altered transmission seasons due to an increasingly volatile climate may exacerbate the impacts of respiratory viruses. Furthermore, both extreme weather events and long-term climate variation are causing the destruction of health systems and large-scale migrations, reshaping health care delivery in the face of an evolving global burden of viral disease. Because of their immunological immaturity, differences in physiology (e.g., size), dependence on caregivers, and behavioral traits, children are particularly vulnerable to climate change. This investigation into the unique pediatric viral threats posed by an increasingly inhospitable world elucidates potential avenues of targeted programming and uncovers future research questions to effect equitable, actionable change. IMPACT: A review of the effects of climate change on viral threats to pediatric health, including zoonotic, vector-borne, water-borne, and respiratory viruses, as well as distal threats related to climate-induced migration and health systems. A unique focus on viruses offers a more in-depth look at the effect of climate change on vector competence, viral particle survival, co-morbidities, and host behavior. An examination of children as a particularly vulnerable population provokes programming tailored to their unique set of vulnerabilities and encourages reflection on equitable climate adaptation frameworks.