Protective Efficacy of Inactivated Vaccine Against H9N2 Subtype Avian Influenza

In order to observe the protective efficacy of widely-used inactivated H9N2 subtype avian influenza vaccine against,F strain inactivated vaccine was inoculated SPF chickens and Lohhman chickens respectively to analysis and compare the antibody level. 9 strains of H9N2 subtype avian influenza virus(AIV) were isolated from immunized chickens during 2009 to 2010 and the chickens were challenged with F strain vaccine to evaluate the effect of intercross immunization of H9N2 subtype vaccine (F strain) to the 9 isolates. The results showed that the antibody titer of F stain were all above 7 log2 after 3 weeks and the last time of antibody in SPF chickens and in Lohhman chickens was 15 weeks and 11 weeks respectively. The inhibition rates to virus shedding in SPF chickens′ larynx and cloaca with F9,L9,S9,D9 and F strains challenged were all 100% for 7 days post challenge while those with F119,W9,YD,M and D119 were all 90%. The inhibition rates to virus shedding in Lohhman chickens′ larynx and cloaca with L9,F9,S9,D9,W9 and F strains challenge were all 100% for 7 days post challenge while those with F119,YD,M and D119 were all 90%. The rates of virus shedding in the control group chickens′ larynx and cloaca were 10/10 for 7 days post challenge.