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BackgroundHuman 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.Methods and FindingsSera 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.ConclusionsVaccination 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.Trial RegistrationClinicalTrials.gov NCT01168401Lisa Lindesmith and colleagues assess the potential of a candidate virus-like particle (VLP) vaccine to induce antibody responses to antigenically divergent norovirus strains.Editors' SummaryBackgroundWorldwide, noroviruses cause one in five cases of viral gastroenteritis (often called stomach flu or winter vomiting disease), the symptoms of which include nausea, vomiting, and diarrhea. There is no specific treatment for infection with these highly contagious viruses, and no established approach to vaccine development. While most people recover from the symptoms of norovirus infection within a few days, young children and the elderly may become severely ill or die. An estimated annual 300 million cases of norovirus infection contribute to roughly 260,000 deaths, mostly among this vulnerable demographic and mostly in low-income countries. Like influenza viruses, many noroviruses are evolving via a process known as antigenic drift. Antigens are components of infectious agents (including viruses) that are recognized by antibodies, proteins that bind to and neutralize foreign invaders. Over time, noroviruses develop small changes in their antigens that allow them to escape from antibodies produced in response to earlier infections. Every two to four years, because of accumulated antigenic drift, a new strain of norovirus emerges to which the human population has no direct antibody immunity, and an outbreak occurs. Because vaccines usually contain a component of the infectious agent that stimulates immunity, antigenic drift complicates the process of vaccine development. To be worth the cost and effort, a norovirus vaccine must confer immunity against a diverse range of norovirus strains, ideally including strains beyond those represented within the vaccine itself.Partly because there is not a reliable method for growing noroviruses in the laboratory, recent efforts have focused on developing candidate vaccines using virus-like particles (VLPs). VLPs are constructed from laboratory-generated molecules of the virus’s capsid (outer shell). These capsid proteins self-assemble into icosahedral VLPs, which resemble the viral shell. VLPs cannot infect people or cause illness, but because they contain viral antigens, they can induce the immune system to produce antibodies that may neutralize actual viruses. VLPs can also be used to study the antibodies that people produce in response to vaccination or infection.Why Was This Study Done?VLP-based vaccines are relatively new, and their capacity to elicit a broad immune response conferring protection to an evolving range of norovirus strains is not established. One VLP vaccine based on a single strain that circulates primarily in children conferred immunity to that strain. Another, multivalent (containing a mix of VLPs from more than one strain) VLP vacci |
