Abstract: The aim was to know about the immune level for AI in Northwest Hubei region. 2311 blood samples were selected from chickens that were inoculated with AIV H9 vaccine in 65 large scale henneries of Northwest Hubei region from Aug 2007 to May 2010. The monitoring and investigation were conducted on serum AI H9 antibody level of chickens by using ELISA method. The investigation showed that in 2007 inspected 135 serums, the positive number was 104, with total positive rate of 77.0%, in which, samples with strong positive antibody were 83, making up 61.5%; in 2008 inspected 985 serums, the positive number was 883, with total positive rate of 89.6%,in which, samples with strong positive antibody were 732, making up 74.3%; in 2009 inspected 433 serums,the positive number was 348, with total positive rate of 80.4%,in which, samples with strong positive antibody were 277, making up 64.0%; in 2010（till May） inspected 758 serums, the positive number was 638, with total positive rate of 84.2%, in which, samples with strong positive antibody were 575, making up 75.6%. The statistic analysis indicated that, of inspected 11 henneries in 2007, there were 4 henneries that had the qualified rate of herd immunity of 75%, accounting for 36.4%; of inspected 25 henneries in 2008, there were 21 henneries that had the qualified rate of herd immunity of 75%, accounting for 84.0%; of inspected 16 henneries in 2009, there were 12 henneries that had the qualified rate of herd immunity of 75%, accounting for 75.0%. The investigation indicated that although strong positive rate of AIV H9 antibody level was relatively low in 2007, the rate had made an obvious increase from Jan 2008 to May 2010. Only partly inspected henneries were in good immune condition, and there were a big difference toward qualified rate of each henneries.

Key words: Northwest Hubei; H9 subtype; avian influenza; antibody