Antigenically and Genetically Diverse Isolates of Low Pathogenicity H9N2 Avian Influenza Virus Provide Cross-Clade Vaccinal Protection

Abstract

Avian influenza viruses, H9N2 subtype, are endemic in Asia and the Middle East. The Israeli H9N2 (G1 lineage) consists of five phylogenetic clades that were detected in the country since the year 2000. The influence of the inter-clade genetic differences on vaccine efficacy was evaluated by vaccination-challenge trials in specific pathogen free (SPF) chickens. Experimental vaccines utilizing isolates belonging to Israeli H9 clades IV and V were prepared with Montanide ISA 70VG adjuvant. When challenged with H9 AIV strains from different genetic clades and antigenic groups provided similar protection, indicating the existence of cross-genetic clade protection (i.e. reduction in amount of virus shed and number of chickens shedding virus). Notably, the protection conferred by both experimental vaccines was highly dependent on the infection dose of the challenge virus.