Protection of chickens against infectious bronchitis virus with a multivalent DNA vaccine and boosting with an inactivated vaccine

Yan, Fang; Zhao, Yujun; Hu, Yongting; Qiu, Jianyang; Lei, Wenxin; Ji, Wenhui; Li, Xuying; Wu, Qian; Shi, Xiumin; Li, Zhong

To evaluate the protective efficacy of the DNA vaccines and prime-boost vaccination strategy we developed, all chickens were challenged with virulent IBVSX16 virus. Mortality and protection rates for the different groups are shown in Table 2 . The number of chickens positive for IBV was determined by RT-PCR analysis of birds that died from viral infection and ones that were euthanized. Mortality was determined as the number of dead chickens divided by the total number of chickens in each group. Protection rate was measured as a percentage of the number of chickens negative for IBV over the total number of chickens. Chickens in the pVAX1-inocluated group developed clinical signs of infection including coughing, nasal discharge, and dyspnea. Mortality rate of the pVAX1injected groups was 35% 14 days post-challenge. In contrast, the protection rates were 75% for the pVAX1-16S1 group, 60% for the pVAX1-16M group, 80% for the pVAX1-16N group, 90% for the pVAX1-16S1/M/N group, 80% for birds given the inactivated vaccine (80%), and 100% for the pVAX1-16S1/M/N + inactivated vaccine animals. The mortality rate was 5% for the pVAX1-16S1/ M/N group, 10% for the inactivated vaccine group, and 0% for birds treated with pVAX1-16S1/M/N + inactivated vaccine.