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Journal of Virology, September 2007, p. 9238-9248, Vol. 81, No. 17
0022-538X/07/$08.00+0     doi:10.1128/JVI.00893-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

A New Generation of Modified Live-Attenuated Avian Influenza Viruses Using a Two-Strategy Combination as Potential Vaccine Candidates

Department of Veterinary Medicine, University of Maryland, College Park, and Virginia-Maryland Regional College of Veterinary Medicine, 8075 Greenmead Drive, College Park, Maryland 20742-3711,¹ Facultad de Medicina Veterinaria y Zootecnia, Universidad Nacional de Colombia, Bogotá, Colombia²

Received 26 April 2007/ Accepted 13 June 2007

In light of the recurrent outbreaks of low pathogenic avian influenza (LPAI) and highly pathogenic avian influenza (HPAI), there is a pressing need for the development of vaccines that allow rapid mass vaccination. In this study, we introduced by reverse genetics temperature-sensitive mutations in the PB1 and PB2 genes of an avian influenza virus, A/Guinea Fowl/Hong Kong/WF10/99 (H9N2) (WF10). Further genetic modifications were introduced into the PB1 gene to enhance the attenuated (att) phenotype of the virus in vivo. Using the att WF10 as a backbone, we substituted neuraminidase (NA) for hemagglutinin (HA) for vaccine purposes. In chickens, a vaccination scheme consisting of a single dose of an att H7N2 vaccine virus at 2 weeks of age and subsequent challenge with the wild-type H7N2 LPAI virus resulted in complete protection. We further extended our vaccination strategy against the HPAI H5N1. In this case, we reconstituted an att H5N1 vaccine virus, whose HA and NA genes were derived from an Asian H5N1 virus. A single-dose immunization in ovo with the att H5N1 vaccine virus in 18-day-old chicken embryos resulted in more than 60% protection for 4-week-old chickens and 100% protection for 9- to 12-week-old chickens. Boosting at 2 weeks posthatching provided 100% protection against challenge with the HPAI H5N1 virus for chickens as young as 4 weeks old, with undetectable virus shedding postchallenge. Our results highlight the potential of live att avian influenza vaccines for mass vaccination in poultry.

Published ahead of print on 27 June 2007.