Broadly neutralizing antibodies that target epitopes of haemagglutinin on the influenza virus have the potential to provide near universal protection against influenza virus infection1. However, viral mutants that escape broadly neutralizing antibodies have been reported2,3. The identification of broadly neutralizing antibody classes that can neutralize viral escape mutants is critical for universal influenza virus vaccine design. Here we report a distinct class of broadly neutralizing antibodies that target a discrete membrane-proximal anchor epitope of the haemagglutinin stalk domain. Anchor epitope-targeting antibodies are broadly neutralizing across H1 viruses and can cross-react with H2 and H5 viruses that are a pandemic threat. Antibodies that target this anchor epitope utilize a highly restricted repertoire, which encodes two public binding motifs that make extensive contacts with conserved residues in the fusion peptide. Moreover, anchor epitope-targeting B cells are common in the human memory B cell repertoire and were recalled in humans by an oil-in-water adjuvanted chimeric haemagglutinin vaccine4,5, which is a potential universal influenza virus vaccine. To maximize protection against seasonal and pandemic influenza viruses, vaccines should aim to boost this previously untapped source of broadly neutralizing antibodies that are widespread in the human memory B cell pool.

Messenger RNA (mRNA) vaccines represent a new, effective vaccine platform with high capacity for rapid development. Generation of a universal influenza virus vaccine with the potential to elicit long-lasting, broadly cross-reactive immune responses is a necessity for reducing influenza-associated morbidity and mortality. Here we focus on the development of a universal influenza B virus vaccine based on the lipid nanoparticle-encapsulated nucleoside-modified mRNA (mRNA-LNP) platform. We evaluate vaccine candidates based on different target antigens that afford protection against challenge with ancestral and recent influenza B viruses from both antigenic lineages. A pentavalent vaccine combining all tested antigens protects mice from morbidity at a very low dose of 50 ng per antigen after a single vaccination. These findings support the further advancement of nucleoside-modified mRNA-LNPs expressing multiple conserved antigens as universal influenza virus vaccine candidates.

Combined vaccine formulations targeting not only hemagglutinin but also other influenza virus antigens could form the basis for a universal influenza virus vaccine that has the potential to elicit long-lasting, broadly cross-reactive immune responses. Lipid nanoparticle (LNP)-encapsulated messenger RNA (mRNA) vaccines can be utilized to efficiently target multiple antigens with a single vaccine. Here, we assessed the immunogenicity and protective efficacy of nucleoside-modified mRNA-LNP vaccines that contain four influenza A group 2 virus antigens (hemagglutinin stalk, neuraminidase, matrix protein 2, and nucleoprotein) in mice. We found that all vaccine components induced antigen-specific cellular and humoral immune responses after administration of a single dose. While the monovalent formulations were not exclusively protective, the combined quadrivalent formulation protected mice from all challenge viruses, including a relevant H1N1 influenza virus group 1 strain, with minimal weight loss. Importantly, the combined vaccine protected from morbidity at a dose of 125 ng per antigen after a single vaccination in mice. With these findings, we confidently conclude that the nucleoside-modified mRNA-LNP platform can be used to elicit protection against a large panel of influenza viruses.

The burden of influenza remains substantial despite unremitting efforts to reduce the magnitude of seasonal influenza epidemics and prepare for pandemics. Although vaccination remains the mainstay of these efforts, current vaccines are designed to stimulate an immune response against the viral hemagglutinin.

Mucosal vaccines and vaccines that block pathogen transmission are under-appreciated in vaccine development. However, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has shown that blocking viral transmission is an important attribute of efficient vaccines. Here, we investigated if recombinant influenza virus neuraminidase (NA) vaccines delivered at a mucosal site could protect from onward transmission of influenza B viruses in the guinea pig model. We tested four different scenarios in which sequential transmission was investigated in chains of four guinea pigs. The variables tested included a low and a high viral inoculum (104vs 105plaque forming units) in the initial donor guinea pig and variation of exposure/cohousing time (1 day vs 6 days). In three out of four scenarios – low inoculum-long exposure, low inoculum-short exposure and high inoculum-short exposure – transmission chains were efficiently blocked. Based on this data we believe an intranasal recombinant NA vaccine could be used to efficiently curtail influenza virus spread in the human population during influenza epidemics.