Broadly Reactive H2 Hemagglutinin Vaccines Elicit Cross-Reactive Antibodies in Ferrets Pre-Immune to Seasonal Influenza A Viruses

Abstract

Influenza vaccines have traditionally been tested in naïve mice and ferrets. However, humans are first exposed to influenza viruses within the first few years of life. Therefore, there is a pressing need to test influenza virus vaccines in animal models that have been previously exposed to influenza viruses before being vaccinated. In this manuscript, previously described H2 computationally optimized broadly reactive antigen (COBRA) HA vaccines (Z1, Z5) were tested in influenza virus 'pre-immune' ferret models. Ferrets were infected with historical, seasonal influenza viruses to establish pre-immunity. These pre-immune ferrets were then vaccinated with either COBRA H2 HA recombinant proteins or WT H2 HA recombinant proteins in a prime-boost regimen. A set of naïve pre-immune or non pre-immune ferrets were also vaccinated to control the effects of the multiple different pre-immune states. All ferrets were then challenged with a swine H2N3 influenza virus. Ferrets with pre-existing immune responses influenced recombinant H2 HA elicited antibodies following vaccination as measured by HAI and classical neutralization assays. Having both H3N2 and H1N1 immunological memory, regardless of the order of exposure, significantly decreased viral nasal wash titers and completely protected all ferrets from both morbidity and mortality, including the mock vaccinated ferrets. While the vast majority of the pre-immune ferrets were protected from both morbidity and mortality across all of the different pre-immune states, the Z1 COBRA HA vaccinated ferrets had significantly higher antibody titers and recognized the largest number H2 influenza viruses in a classical neutralization assay compared to the other H2 HA-based vaccines.