Non-propagating RNA virus-vectored HA/NA vaccine prevents shedding of antigen-drifted H1N1 influenza virus in pigs.

Seasonal influenza viruses evade immunity through antigenic drift, enabling escape from inhibitory antibodies targeting hemagglutinin (HA) and neuraminidase (NA). In this study, we evaluated a non-propagating vesicular stomatitis virus (VSV) vector encoding HA and NA antigens of A/Hamburg/4/2009 (H1N1) in a porcine animal model to assess induction of cross-reactive immunity. A single intramuscular immunization elicited high titers of H1N1-neutralizing antibodies and potent N1-sialidase inhibition. A boost with the same single-cycle VSV-vectored H1/N1 antigens or with a live-attenuated influenza vaccine (LAIV) enhanced inhibitory activity against the antigen-drifted A/Victoria/2570/2019 (H1N1) strain. Vaccination induced N1-specific antibodies that also inhibited avian N1 sialidase and suppressed replication of a bovine-derived H5N1 virus in vitro. Following nasal challenge with a 6:2 reassortant virus encoding drifted HA and NA antigens, vaccinated pigs showed no detectable virus shedding, whereas control animals shed infectious virus. Homologous prime-boost vaccination with the VSV-vectored H1/N1 antigens conferred protection comparable to the heterologous VSV/LAIV regimen in the upper respiratory tract. These findings demonstrate that a single-cycle VSV vector encoding both HA and NA induces cross-protective immunity against antigen-drifted influenza viruses, reduces the risk of vaccine mismatch, and may limit infection by zoonotic H5N1 viruses.