Submitted to: Journal of Applied Poultry Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/5/2007
Publication Date: 3/1/2008
Citation: Goetz, S., Spackman, E., Hayhow, C., Swayne, D.E. 2008. Assessment of reduced vaccine dose on efficacy of an inactivated avian influenza vaccine against an H5N1 high pathogenicity avian influenza virus. Journal of Applied Poultry Research. 17:145-150. Interpretive Summary: Avian influenza (AI) vaccines for poultry can be used in an emergency to control high pathogenicity AI. However, the available doses of inactivated AI vaccine are limited. A study was conducted to determine if the available vaccine doses could be extended using reduced vaccine dose regimes, but maintain adequate protection in chickens. The average protective dose was 1/50 dose and, using the international standard of 50 PD50, the full manufacturer's dose of the H5N9 AI vaccine would be the minimum dose in emergency.
Technical Abstract: Avian influenza (AI) vaccines have emerged to be a viable emergency tool for use in a comprehensive strategy for dealing with high pathogenicity (HP) AI in developed countries. However, the available doses of inactivated AI vaccine are limited to national vaccine banks and inventory stocks of some commercial biologics manufacturers. To determine if the available vaccine doses could be stretched by using reduced vaccine dose but maintain adequate efficacy, a study was conducted to determine if 3-week-old specific-pathogen-free white leghorn chickens vaccinated with full, 1/2, 1/4, and 1/10 dose of an inactivated H5N9 AI vaccine would be protected against a high dose challenge of H5N1 HPAI virus given four weeks later. At all four AI vaccine doses, the AI vaccinated chickens were protected from disease and death, but all the sham vaccinated chickens developed clinical signs and died. There were no differences between the full, 1/2 and 1/4 dose AI vaccine groups for serological titers at 7 weeks of age, or for cloacal and oropharyngeal titers of challenge virus shed at 2 days post challenge. However, the 1/10 dose group had significantly reduced hemagglutination inhibition (HI) titers at 7 weeks compared to 1/4 dose, and the 1/10 dose group had more chickens shedding challenge virus from the oropharynx than the full dose group. Most importantly, the mean protective dose (PD50) was 1/50 dose and using the international regulatory standard of 50 PD50 for Newcastle disease vaccine as a guide, the full dose of the H5N9 AI vaccine would be the minimum dose acceptable for use in the field. Use of the full vaccine dose is especially important because protection in commercial chickens in the field is typically less than seen in experimental studies in specific pathogen free chickens in the laboratory.