Intranasal Mosaic H1N1 Live Attenuated Influenza Vaccine Elicits Broad Cross-Reactive Immunity and Protection Against Group 1 and 2 Influenza A Viruses.

Influenza, a highly pathogenic infectious disease, causes nearly half a million deaths annually worldwide. Thus, effective vaccine-based prevention and control are crucial. Although live attenuated influenza vaccines (LAIVs) can induce mucosal immunity, existing vaccines effectiveness remains relatively low, posing a significant threat to public health. Thus, we developed a novel mosaic H1N1 LAIV candidate by integrating mosaic antigen design with established LAIV technology. This vaccine incorporates most potential T-cell epitopes of hemagglutinin and neuraminidase antigens into an attenuated master donor strain, ensuring safety and broad immunity. We compared it with commercial monovalent attenuated and inactivated vaccines in mice. The mosaic H1N1 LAIV induced robust cross-reactive humoral and mucosal immune responses, enhanced antigen-specific cellular immunity, and established tissue-resident memory T and B cells in the respiratory tract. Challenge experiments confirmed its protective efficacy against homologous and heterologous strains. It provided complete protection against homologous strains with low epitope similarity and partial protection against the ancestral H3N2 virus. Our study highlights the mosaic H1N1 LAIV as an excellent universal vaccine candidate capable of inducing broad cross-reactive immune responses and providing robust protection against distinct influenza A viruses, demonstrating a promising strategy to address the limitations of current commercial vaccines.