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Human noroviruses (NoVs) are the primary cause of acute gastroenteritis and are characterized by antigenic variation between genogroups and genotypes and antigenic drift of strains within the predominant GII.4 genotype. In the context of this diversity, an effective NoV vaccine must elicit broadly protective immunity. We used an antibody (Ab) binding blockade assay to measure the potential cross-strain protection provided by a multivalent NoV virus-like particle (VLP) candidate vaccine in human volunteers. Sera from ten human volunteers immunized with a multivalent NoV VLP vaccine (genotypes GI.1/GII.4) were analyzed for IgG and Ab blockade of VLP interaction with carbohydrate ligand, a potential correlate of protective immunity to NoV infection and illness. Immunization resulted in rapid rises in IgG and blockade Ab titers against both vaccine components and additional VLPs representing diverse strains and genotypes not represented in the vaccine. Importantly, vaccination induced blockade Ab to two novel GII.4 strains not in circulation at the time of vaccination or sample collection. GII.4 cross-reactive blockade Ab titers were more potent than responses against non-GII.4 VLPs, suggesting that previous exposure history to this dominant circulating genotype may impact the vaccine Ab response. Further, antigenic cartography indicated that vaccination preferentially activated preexisting Ab responses to epitopes associated with GII.4.1997. Study interpretations may be limited by the relevance of the surrogate neutralization assay and the number of immunized participants evaluated. Vaccination with a multivalent NoV VLP vaccine induces a broadly blocking Ab response to multiple epitopes within vaccine and non-vaccine NoV strains and to novel antigenic variants not yet circulating at the time of vaccination. These data reveal new information about complex NoV immune responses to both natural exposure and to vaccination, and support the potential feasibility of an efficacious multivalent NoV VLP vaccine for future use in human populations. ClinicalTrials.gov NCT01168401.

Background. The effect of vitamin A supplementation on viral gastrointestinal infections among young children living in developing countries remains unclear. Methods. The effect of vitamin A supplementation on norovirus (NoV) infection among 127 Mexican children 5–15 months of age was studied in a randomized, placebo-controlled trial during June-August 1998. Stool samples collected every 2 weeks and after diarrheal episodes were screened for NoV and characterized at the genogroup level (GI and GII). Results. Of the stool samples collected, 29.9% were positive for NoV, and NoV GI and NoV GII were found in 55.4% and 46.4% of the positive samples, respectively. Vitamin A supplementation reduced the prevalence of NoV GII infections (rate ratio [RR], 0.60 [95% confidence interval {CI}, 0.20–0.82]), increased the length of both NoV GI and GII shedding, and decreased the prevalence of NoV-associated diarrhea (RR, 0.51 [95% CI, 0.26–0.97]). Conclusions. These findings suggest that NoV is an important cause of pediatric diarrhea in this study population and that vitamin A supplementation has divergent effects on specific outcomes of NoV infection.

Norovirus GII.17 outbreaks in the United States increased from <10% during the 2022-23 season to 75% during the 2024-25 season, surpassing the number of GII.4 outbreaks. The norovirus season also started earlier in 2024-25 than in previous seasons. Continued norovirus surveillance is needed to detect and monitor emerging strains.

Noroviruses belong to a genus of genetically diverse viruses within the family Caliciviridae and cause acute gastroenteritis in humans and animals. They are subdivided into genogroups, each of which further segregates into genotypes. Until recently, a new genotype was based on a defined pairwise distance cutoff of complete VP1 sequences, but with the increasing number of available norovirus sequences, this cutoff is no longer accurate, and sequences in the public database have been misclassified. In this paper, we demonstrate that the pairwise distance cutoff method can no longer be used and outline a phylogenetic approach to classify noroviruses. Furthermore, we propose a dual nomenclature using both ORF1 and VP1 sequences, as recombination is common and recognizing recombinant viruses may be relevant. With the continuing emergence of new norovirus lineages, we propose to coordinate nomenclature of new norovirus genotypes through an international norovirus working group.

Human noroviruses are recognised as the major global cause of viral gastroenteritis. Here, we provide an overview of notable advances in norovirus research and provide a short recap of the novel model systems to which much of the recent progress is owed. Significant advances include an updated classification system, the description of alternative virus-like protein morphologies and capsid dynamics, and the further elucidation of the functions and roles of various viral proteins. Important milestones include new insights into cell tropism, host and microbial attachment factors and receptors, interactions with the cellular translational apparatus, and viral egress from cells. Noroviruses have been detected in previously unrecognised hosts and detection itself is facilitated by improved analytical techniques. New potential transmission routes and/or viral reservoirs have been proposed. Recent in vivo and in vitro findings have added to the understanding of host immunity in response to norovirus infection, and vaccine development has progressed to preclinical and even clinical trial testing. Ongoing development of therapeutics includes promising direct-acting small molecules and host-factor drugs.

Porcine noroviruses and sapoviruses belong to the family Caliciviridae and are rarely reported in European countries. In this study, swine stools from a region representative of northern Europe were screened for these viruses by RT-PCR. Both porcine noroviruses and sapoviruses were detected, showing their circulation in this region. The porcine norovirus strains were genetically related to genotype 19 strains in the genogroup II of the genus Norovirus. The porcine sapovirus strains were genetically related to the porcine enteric calicivirus Cowden reference strain and to newly described porcine strains in the genus Sapovirus.

Norovirus is a major cause of acute gastroenteritis; GII.4 is the predominant strain in humans. Recently, 2 new GII.4 variants, Hong Kong 2019 and San Francisco 2017, were reported. Characterization using GII.4 monoclonal antibodies and serum demonstrated different antigenic profiles for the new variants compared with historical variants.

Noroviruses are now recognized as the leading cause of epidemics of gastroenteritis and an important cause of sporadic gastroenteritis among both children and adults. In the United States, more than 90% of the outbreaks of gastroenteritis for which the cause could not previously be identified can now be attributed to this virus. Understanding the nature of immunity to the norovirus is a key determinant for future improvements in the control and prevention of this viral infection. Noroviruses are now recognized as the leading cause of epidemics of gastroenteritis. Understanding the nature of immunity to the norovirus is a key determinant for future improvements in the control and prevention of this viral infection. The Norwalk agent was the first virus that was identified as causing gastroenteritis in humans, but recognition of its importance as a pathogen has been limited because of the lack of available, sensitive, and routine diagnostic methods. Recent advances in understanding the molecular biology of the noroviruses, coupled with applications of novel diagnostic techniques, have radically altered our appreciation of their impact. Noroviruses are now recognized as being the leading cause of epidemics of gastroenteritis and an important cause of sporadic gastroenteritis in both children and adults. Although norovirus gastroenteritis is generally mild and of short duration, new evidence suggests . . .

Over the past two years, increased norovirus activity has been reported in multiple countries, accompanied by a rise in genotype GII.17 prevalence. Despite causing large outbreaks in Asia during 2014-2016, GII.17 has not historically been considered a predominant genotype. In this study, using 1471 archival and newly-identified GII.17 genomes, we investigated (i) global diversification patterns of this virus at the whole-genome level, (ii) in-depth mutational patterns within 511 viruses detected during a 10-year national survey in Germany, and (iii) intra-host viral diversity and adaptation processes that lead to the predominance of the GII.17 virus. The recent GII.17 norovirus exhibited extensive genetic diversity and multiple back-and-forth and recurrent mutations during the early phase of its epidemic; however, this diversity declined by 2024, suggesting that the virus had reached a phenotype efficient for human infection. Experimental data confirmed that mutations in the viral capsid enhanced binding to host factors associated with virus entry and resulted in antigenic changes compared to previously circulating clusters. Overall, this study demonstrated that the recent surge of GII.17 resulted from a dynamic, multifaceted process involving diverse adaptive strategies, ultimately enabling the virus to achieve sustained transmission within the human population. Norovirus genotype GII.17 has been linked with a recent increase in cases in Europe and the Americas. Here, the authors investigate the genetic diversity and mutational patterns, and phenotypic differences associated with the recent circulating strain.

Norovirus genogroup II genotype 4 (GII.4) has been the predominant cause of viral gastroenteritis since 1996. Here we show that during the winter of 2014–2015, an emergent variant of a previously rare norovirus GII.17 genotype, Kawasaki 2014, predominated in Hong Kong and outcompeted contemporary GII.4 Sydney 2012 in hospitalized cases. GII.17 cases were significantly older than GII.4 cases. Root-to-tip and Bayesian BEAST analyses estimate GII.17 viral protein 1 (VP1) evolves one order of magnitude faster than GII.4 VP1. Residue substitutions and insertion occur in four of five inferred antigenic epitopes, suggesting immune evasion. Sequential GII.4-GII.17 infections are noted, implicating a lack of cross-protection. Virus bound to saliva of secretor histo-blood groups A, B and O, indicating broad susceptibility. This fast-evolving, broadly recognizing and probably immune-escaped emergent GII.17 variant causes severe gastroenteritis and hospitalization across all age groups, including populations who were previously less vulnerable to GII.4 variants; therefore, the global spread of GII.17 Kawasaki 2014 needs to be monitored. Norovirus GII.4 has been predominating in viral gastroenteritis for 20 years. Here the authors report the emergence and predominance of a novel fast-evolving GII.17 lineage norovirus causing viral gastroenteritis in Hong Kong, with a shift in age distribution of affected individuals towards an older age as compared to GII.4.