Fig. 1

Seroconversion after immunization with the commercial H9N2 AIV inactivated vaccine in commercial broilers and SPF chickens. Each 1-day-old broiler (a) and 1-day-old SPF chicken (b) in Group one was subcutaneously inoculated with 0.1 mL of the commercial H9N2 AIV inactivated vaccine. Each 21-day-old broiler (c) and 21-day-old SPF chicken (d) in Group two was subcutaneously inoculated with 0.3 mL of commercial H9N2 AIV inactivated vaccine. The same number of SPF chickens and broilers in Group three of the same age were not vaccinated and served as a negative control. Serum H9N2-specific antibody responses were measured weekly. The symbol (*) denotes differences between two groups at the same time point (* P < 0.05, ** P < 0.01, and *** P < 0.001)