A subunit vaccine candidate derived from a classic H5N1 avian influenza virus in China protects fowls and BALB/c mice from lethal challenge

In recent years, numerous human infections with avian influenza viruses in Asia have raised the concern that the next influenza pandemic is imminent. The most effective way to combat human avian influenza is through vaccination of the public. In this study, we developed an influenza A recombinant protein (rH5HA) directed against the hemagglutinin (HA) of a classic H5N1 high pathogenic avian influenza virus isolated in South China in 1996. Following purification of the recombinant protein expressed from a baculovirus expression system, we evaluated the efficiency of rH5HA on specific pathogen free (SPF) chicken, commercial chicken, and in BALB/c mice in an infection-protection model. The results demonstrated that rH5HA induced antibody responses and provided full protection in both SPF chickens and commercial chickens. Protective immunity was generated within 2 weeks in chickens as young as 7-day post-hatch using a minimum amount of rH5HA protein (2 μg/bird/vaccination). The serum antibody generated from rH5HA immunization was protective and lasted more than 6 months. Our data also demonstrated that rH5HA immunization protected BALB/c mice from a lethal challenge with pathogenic avian influenza virus. These results suggested that vaccination with rH5HA could be a vaccine candidate for the control of H5N1 avian influenza in poultry, in mice, and potentially in other mammals including human.