Delegates at the 150th annual meeting of the American Veterinary Medical Association (AVMA) recently heard about the emergence of a strain of the high pathogenic avian influenza A(H5N1) virus in Indonesia that are resistant to vaccines.
Vaccines have been used to protect poultry in Asia against H5N1 high pathogenicity avian influenza (HPAI) since 2002.
However, David E. Swayne and colleagues at the US Department Of Agriculture, Agricultural Research Service, Southeast Poultry Research Laboratory told the AVMA meeting in Chicago in July that reports of vaccine “failures” began to emerge in 2006 in Indonesia, with identification of clinical disease consistent with HPAI or isolation of H5N1 HPAIV in vaccinated flocks or in regions that vaccinate.
In their study, H5N1 HPAI field viruses from Indonesia were examined genetically and antigenically to identify variants, and three viruses were selected for challenge studies against classic H5 avian influenza vaccine seed strains.
An antigenic drift variant H5N1 HPAI virus (A/Chicken/West Java/PWT-WIJ/2006 [PWT/06]) was identified in Indonesia that was not protected by classic H5 AI vaccines.
Usage of the parent HPAI virus protected chickens from lethal challenge. A reverse genetics (rg) low pathogenicity avian influenza (LPAI) virus seed strains were constructed using the haemagglutinin gene of A/Chicken/West Java/PWT-WIJ/2006 (H5N1), and one of the clones protected chickens against challenge by the HPAI parent strain.
These studies indicate that antigenic variants did emerge in Indonesia following widespread H5 avian influenza vaccine usage, and new vaccine seed strains for inactivated vaccines can be developed based on the HPAI parent virus or, a better alternative for biosecurity and manufacturing, is the development and use of rg-LPAI seed strains to correct vaccine failures, producing the next generation efficacious vaccine seed strains.
(Source – http://www.blackseagrain.net/about-ukragroconsult/news-bsg/indonesia.-bird-flu-vaccine-failures-in-indonesia-investigated)