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1 March 2007 Efficacy of a Fowlpox-Vectored Avian Influenza H5 Vaccine Against Asian H5N1 Highly Pathogenic Avian Influenza Virus Challenge
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A recombinant fowlpox-avian influenza (AI) H5 vaccine (rFP-AIV-H5) expressing the hemagglutinin of the A/turkey/Ireland/1378/83 H5N8 AI isolate has been used in Central America since 1998 to control H5N2 low pathogenicity AI. Previously, this vaccine was shown to induce full protection against a panel of H5 highly pathogenic (HP) AI isolates, including HPAI H5N1. Here, we evaluate the efficacy of rFP-AIV-H5 against escalating doses of HPAI H5N1 A/chicken/SouthKorea/ES/03 isolate and against the HPAI H5N1 A/chicken/Vietnam/0008/2004 isolate. In both studies, 1-day-old specific pathogen-free (SPF) chickens were vaccinated by subcutaneous route with rFP-AIV-H5 and challenged 3 wk later by the oronasal route. In the first study, full protection was observed up to a challenge dose of 6.5 log10 embryo infectious dose (EID50), and the 50% chicken infectious dose was estimated to be 3.1 and 8.5 log10 EID50 in the control and the rFP-AIV-H5-vaccinated group, respectively. A 2–4 log10 and >4 log10 reduction of oral and cloacal shedding was observed in rFP-AIV-H5 vaccinated birds, respectively. The rFP-AIV-H5 vaccine induced hemagglutination inhibition antibodies (5.2 log2) detectable with homologous H5N8 antigen. In the second study, rFP-AIV-H5-vaccinated chicks were fully protected against morbidity and mortality after challenge with the 2004 Vietnam isolate, whereas unvaccinated chickens died within 2 days of challenge. Shedding in cloacal swabs was detected in all unvaccinated controls but in none of the rFP-AIV-H5-vaccinated chickens. Together, these results confirm the excellent level of protection induced by rFP-AIV-H5 in SPF chickens against two recent Asian HPAI H5N1 isolates.

Michel Bublot, Nikki Pritchard, Julio S. Cruz, Thomas R. Mickle, Paul Selleck, and David E. Swayne "Efficacy of a Fowlpox-Vectored Avian Influenza H5 Vaccine Against Asian H5N1 Highly Pathogenic Avian Influenza Virus Challenge," Avian Diseases 51(s1), 498-500, (1 March 2007).
Received: 27 April 2006; Accepted: 1 August 2006; Published: 1 March 2007

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