A dual-adjuvanted HA stem nanoparticle vaccine elicits a multifunctional antibody response that is associated with protection in newborn monkeys

The absence of an approved influenza vaccine for young infants, combined with the annual requirement for updates, underscores the urgent need for a universal vaccine that is effective in newborns. The H1ssF vaccine, an influenza hemagglutinin stem-bearing nanoparticle, generates broadly protective responses in adult animal models and humans. Here, we use a nonhuman primate model to explore the ability of H1ssF, adjuvanted with R848 and AddaVax, to induce a protective response in the altered immune setting of newborns. We find that the vaccine induces strong stem-specific IgG responses that are broadly reactive. Notably, the vaccine promotes antibodies with neutralizing activity and broad Fc effector functions in all newborns. Finally, administration of this vaccine confers improved viral clearance after challenge. These findings demonstrate the potential of this dual-adjuvanted stem nanoparticle to serve as an effective vaccine approach that can elicit protective responses in newborns against influenza A virus infection.