Efficacy of vaccines in chickens against highly pathogenic Hong Kong H5N1 avian influenza

In 1997, highly pathogenic (HP) H5N1 avian influenza virus (AIV) caused inf ections in poultry in Hong Kong and crossed into humans, resulting in a lim ited number of infections including 18 hospitalized cases and six associate d deaths. The unique ability of this, AIV to infect both poultry and people raised a concern for the potential of humans to be biological as well as m echanical vectors of this AIV to poultry. The current study was undertaken to determine if existing vaccines and their technologies could be used duri ng an outbreak ro protect poultry. Commercial and experimental inactivated whole H5 AIV and baculovirus-expressed AIV H5 hemagglutinin protein vaccine s provided protection from clinical signs and death in chickens after letha l challenge by human-origin HP H5N1 Hong Kong strains 156/97 and 483/97. Th e commercial and experimental inactivated vaccines had mean protective dose s ranging from 0.25 to 0.89, which represents the milligrams of viral prote in in the vaccines that provided protection from death in half of the birds . Furthermore, the vaccines reduced the ability of the challenge AIV to rep licate in chickens and decreased the recovery of challenge AIV from the ent eric and respiratory tracts, but the use of a vaccine will not totally prev ent AI virus replication and shedding. Existing vaccines will protect poult ry from mortality and reduce virus replication from the new HP AIV strain t hat can infect both poultry and humans.