Characterization and efficacy determination of commercially available Central American H5N2 avian influenza vaccines for poultry.

A poultry vaccination program was implemented in Central America beginning in January 1995 to control both H5N2 low (LPAI) and high pathogenicity avian influenza. This study was conducted to identify seed strain composition and the efficacy of 10 commercially available H5 vaccines against challenge with H5N2 LPAI viruses isolated from Latin America in 2003. The original 1994 vaccine seed virus in commercial inactivated vaccines did not significantly reduce challenge virus shed titers. However, two seed strains of inactivated vaccines, genetically more closely related to the challenge virus, did significantly reduce titers of challenge virus shed from respiratory tract. In addition, a live recombinant fowlpox virus vaccine containing a more distantly related Eurasian lineage H5 gene insert significantly reduced respiratory shedding as compared to sham vaccinates. These results demonstrate the feasibility of identifying vaccine seed strains in commercial finished products for regulatory verification and the need for periodic challenge testing against current field strains in order to select efficacious vaccine seed strains.