Selection and evaluation of H9N2 avian influenza inactivate vaccine candidates

In this study,candidate vaccine strains were selected from fifteen H9N2 subtype avian influenza viruses(AIV) isolated from eight provinces in mainland China during 2008. Six vaccine strains including CK/ZJ/17/08,CK/SD/2CZ/08,DK/FJ/560/08,CK/FJ/521/08,CK/HuN/174/08 and CK/HuN/33/08 were selected based on the antigenic analysis. The immune efficacy of the strains was evaluated by inoculaing SPF chickens with oil-emulsion inactivated vaccines prepared from respective strains. The results showed that all vaccine strains could induce high level(10.35 to 11.81 log2) hemagglutination inhibition antibody against homologous H9N2 virus at 3 weeks post-immunization,and the CK/HuN/174/08 and CK/HuN/33/08 inactivated vaccines were shown to protect the SPF chickens from challenge by both homologous and heterologous AIV H9N2 strain. The results indicated that only CK/HuN/174/08 and CK/HuN/33/08,but not all the H9N2 strains,have the potential attributes to be qualified as inactivated vaccine candidates against H9N2 virus in most parts of mainland China.