Adenovirus and mRNA vaccines as well as mucosal boosting improve protective efficacy against influenza virus challenge in macaques.

The clinically approved seasonal influenza vaccines provide only 10 to 60% efficacy, necessitating strategies to improve vaccine performance. Here, we explored strategies for improving influenza vaccine efficacy using gene-based vaccines and mucosal boosting strategies in nonhuman primates. All vaccinated cynomolgus macaques were primed with the clinical quadrivalent inactivated virus (QIV) vaccine. We evaluated a rhesus adenovirus (RhAd52) vector delivered by intramuscular or mucosal routes and an mRNA vaccine encoding the hemagglutinin of A/H1N1/Wisconsin/67/2022 delivered intramuscularly as boosts compared with the QIV vaccine delivered intramuscularly and the quadrivalent live-attenuated influenza virus (LAIV) vaccine delivered intranasally. Boosting with RhAd52 and mRNA vaccines induced more robust humoral and cellular immune responses than the clinically approved vaccines and provided improved protective efficacy against a high-dose homologous challenge with A/H1N1/Wisconsin/67/2022. The RhAd52 vaccine delivered by the intratracheal route elicited robust mucosal antibody and T cell responses and provided optimal protection in the upper and lower respiratory tracts. Both peripheral and mucosal antibody responses, as well as mucosal T cell responses, correlated with protection against viral loads. Altogether, this study defines strategies for improving H1N1 seasonal influenza vaccine efficacy by using gene-based vaccines and by optimizing mucosal immunity.