Zika virus (ZIKV) is spreading rapidly into regions around the world where other flaviviruses, such as dengue virus (DENV) and West Nile virus (WNV), are endemic. Antibody-dependent enhancement has been implicated in more severe forms of flavivirus disease, but whether this also applies to ZIKV infection is unclear. Using convalescent plasma from DENV- and WNV-infected individuals, we found substantial enhancement of ZIKV infection in vitro that was mediated through immunoglobulin G engagement of Fcγ receptors. Administration of DENV- or WNV-convalescent plasma into ZIKV-susceptible mice resulted in increased morbidity—including fever, viremia, and viral loads in spinal cord and testes—and increased mortality. Antibody-dependent enhancement may explain the severe disease manifestations associated with recent ZIKV outbreaks and highlights the need to exert great caution when designing flavivirus vaccines.

Summary SARS-CoV-2 infection has emerged as a serious global pandemic. Because of the high transmissibility of the virus and the high rate of morbidity and mortality associated with COVID-19, developing effective and safe vaccines is a top research priority. Here, we provide a detailed evaluation of the immunogenicity of lipid nanoparticle-encapsulated, nucleoside-modified mRNA (mRNA-LNP) vaccines encoding the full-length SARS-CoV-2 spike protein or the spike receptor binding domain in mice. We demonstrate that a single dose of these vaccines induces strong type 1 CD4 + and CD8 + T cell responses, as well as long-lived plasma and memory B cell responses. Additionally, we detect robust and sustained neutralizing antibody responses and the antibodies elicited by nucleoside-modified mRNA vaccines do not show antibody-dependent enhancement of infection in vitro . Our findings suggest that the nucleoside-modified mRNA-LNP vaccine platform can induce robust immune responses and is a promising candidate to combat COVID-19.

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In an attempt to assess the cross-protective potential of the influenza virus neuraminidase (NA) as a vaccine antigen, different subtypes of recombinant NA were expressed in a baculovirus system and used to vaccinate mice prior to lethal challenge with homologous, heterologous, or heterosubtypic viruses. Mice immunized with NA of subtype N2 were completely protected from morbidity and mortality in a homologous challenge and displayed significantly reduced viral lung titers. Heterologous challenge with a drifted strain resulted in morbidity but no mortality. Similar results were obtained for challenge experiments with N1 NA. Mice immunized with influenza B virus NA (from B/Yamagata/16/88) displayed no morbidity when sublethally infected with the homologous strain and, importantly, were completely protected from morbidity and mortality when lethally challenged with the prototype Victoria lineage strain or a more recent Victoria lineage isolate. Upon analyzing the NA content in 4 different inactivated-virus vaccine formulations from the 2013-2014 season via Western blot assay and enzyme-linked immunosorbent assay quantification, we found that the amount of NA does indeed vary across vaccine brands. We also measured hemagglutinin (HA) and NA endpoint titers in pre- and postvaccination human serum samples from individuals who received a trivalent inactivated seasonal influenza vaccine from the 2004-2005 season; the induction of NA titers was statistically less pronounced than the induction of HA titers. The demonstrated homologous and heterologous protective capacity of recombinant NA suggests that supplementing vaccine formulations with a standard amount of NA may offer increased protection against influenza virus infection.

Better vaccines against influenza virus are urgently needed to provide broader protection against diverse strains, subtypes, and types. Such efforts are assisted by the identification of novel broadly neutralizing epitopes targeted by protective antibodies. Influenza vaccine development has largely focused on the hemagglutinin, but the other major surface antigen, the neuraminidase, has reemerged as a potential target for universal vaccines. We describe three human monoclonal antibodies isolated from an H3N2-infected donor that bind with exceptional breadth to multiple different influenza A and B virus neuraminidases. These antibodies neutralize the virus, mediate effector functions, are broadly protective in vivo, and inhibit neuraminidase activity by directly binding to the active site. Structural and functional characterization of these antibodies will inform the development of neuraminidase-based universal vaccines against influenza virus.

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SummaryInfluenza virus infections induce antibodies against the viral surface glycoproteins hemagglutinin and neuraminidase, and these responses can be broadly protective. To test the breadth and magnitude of antibody responses, mice, guinea pigs and ferrets were sequentially infected with divergent H1N1 or H3N2 viruses. Antibody responses were measured by ELISA against an extensive panel of recombinant glycoproteins representing the viral diversity in nature. Guinea pigs developed high titers of broadly cross-reactive antibodies; mice and ferrets exhibited narrower humoral responses. Then, we compared antibody responses after H1N1 or H3N2 infections in humans and found markedly broad responses and cogent evidence for original antigenic sin. This work will inform universal influenza vaccine design and can guide pandemic preparedness efforts against emerging influenza viruses.

Influenza viruses evade human adaptive immune responses due to continuing antigenic changes. This makes it necessary to re-formulate and re-administer current seasonal influenza vaccines on an annual basis. Our pan-influenza vaccination approach attempts to redirect antibody responses from the variable, immuno-dominant hemagglutinin head towards the conserved—but immuno-subdominant—hemagglutinin stalk. The strategy utilizes sequential immunization with chimeric hemagglutinin-based vaccines expressing exotic head domains, and a conserved hemagglutinin stalk. We compared a live-attenuated influenza virus prime followed by an inactivated split-virus boost to two doses of split-virus vaccines and assessed the impact of adjuvant on protection against challenge with pandemic H1N1 virus in ferrets. All tested immunization regimens successfully induced broadly cross-reactive antibody responses. The combined live-attenuated/split virus vaccination conferred superior protection against pandemic H1N1 infection compared to two doses of split-virus vaccination. Our data support advancement of this chimeric hemagglutinin-based vaccine approach to clinical trials in humans.