Vaccination with VSV-vectored chimeric hemagglutinins protects mice against divergent influenza virus challenge strains.

Seasonal influenza virus infections continue to cause significant disease each year, and there is a constant threat of the emergence of reassortant influenza strains causing a new pandemic. Available influenza vaccines are variably effective each season, are of limited scope at protecting against viruses that have undergone significant antigenic drift, and offer low protection against newly emergent pandemic strains. "Universal" influenza vaccine strategies that focus on the development of humoral immunity directed against the stalk domains of the viral hemagglutinin (HA) show promise for protecting against diverse influenza viruses. Here, we describe such a strategy that utilizes vesicular stomatitis virus (VSV) as a vector for chimeric hemagglutinin (cHA) antigens. This vaccination strategy is effective at generating HA stalk-specific, broadly cross-reactive serum antibodies by both intramuscular and intranasal routes of vaccination. We show that prime-boost vaccination strategies provide protection against both lethal homologous and heterosubtypic influenza challenge and that protection is significantly improved with intranasal vaccine administration. Additionally, we show that vaccination with VSV-cHAs generates greater stalk-specific and cross-reactive serum antibodies than does vaccination with VSV-vectored full-length HAs, confirming that cHA-based vaccination strategies are superior at generating stalk-specific humoral immunity. VSV-vectored influenza vaccines that express chimeric hemagglutinin antigens offer a novel means for protecting against widely diverging influenza viruses. IMPORTANCE Universal influenza vaccination strategies should be capable of protecting against a wide array of influenza viruses, and we have developed such an approach utilizing a single viral vector system. The potent antibody responses that these vaccines generate are shown to protect mice against lethal influenza challenges with highly divergent viruses. Notably, intranasal vaccination offers significantly better protection than intramuscular vaccination in a lethal virus challenge model. The results described in this study offer insights into the mechanisms by which chimeric hemagglutinin (HA)-based vaccines confer immunity, namely, that the invariant stalk of cHA antigens is superior to full-length HA antigens at inducing cross-reactive humoral immune responses and that VSV-cHA vaccine-induced protection varies by site of inoculation, and contribute to the further development of universal influenza virus vaccines.