Live attenuated H5N1 vaccine with H9N2 internal genes protects chickens from infections by both Highly Pathogenic H5N1 and H9N2 Influenza Viruses

BACKGROUND   The highly pathogenic H5N1 and H9N2 influenza viruses are endemic in many countries around the world and have caused considerable economic loss to the poultry industry. Objectives  We aimed to study whether a live attenuated H5N1 vaccine comprising internal genes from a cold-adapted H9N2 influenza virus could protect chickens from infection by both H5N1 and H9N2 viruses. METHODS   We developed a cold-adapted H9N2 vaccine virus expressing hemagglutinin and neuraminidase derived from the highly pathogenic H5N1 influenza virus using reverse genetics. RESULTS AND CONCLUSIONS   Chickens immunized with the vaccine were protected from lethal infections with homologous and heterologous H5N1 or H9N2 influenza viruses. Specific antibody against H5N1 virus was detected up to 11 weeks after vaccination (the endpoint of this study). In vaccinated chickens, IgA and IgG antibody subtypes were induced in lung and intestinal tissue, and CD4+ and CD8+ T lymphocytes expressing interferon-gamma were induced in the splenocytes. These data suggest that a live attenuated H5N1 vaccine with cold-adapted H9N2 internal genes can protect chickens from infection with H5N1 and H9N2 influenza viruses by eliciting humoral and cellular immunity.