Vaccines protect chickens against H5 highly pathogenic avian influenza in the face of genetic changes in field viruses over multiple years

Inactivated whole avian influenza (AI) virus vaccines, baculovirus-derived AI haemagglutinin vaccine and recombinant fowlpoxvirus-AI haemagglutinin va ccine were tested for the ability to protect chickens against multiple high ly pathogenic (HP) H5 AI viruses. The vaccine and challenge viruses, or the ir haemagglutinin protein components, were obtained from field AI viruses o f diverse backgrounds and included strains obtained from four continents, s ix host species, and isolated over a 38-year-period. The vaccines protected against clinical signs and death, and reduced the number of chickens shedd ing virus and the titre of the virus shed following a HP H5 AI virus challe nge. Immunization with these vaccines should decrease AI virus shedding fro m the respiratory and digestive tracts of Al virus exposed chickens and red uce bird-to-bird transmission. Although most consistent reduction in respir atory shedding was afforded when vaccine was more similar to the challenge virus, the genetic drift of avian influenza virus did not interfere with ge neral protection as has been reported for human influenza viruses. (C) 2000 Elsevier Science B.V. All rights reserved.