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

As for the choice of a booster, the inactivated vaccine is prepared from the whole virus particle, so the immune responses induced by inactivated IBV vaccines could respond to the whole virus. The inactivated vaccine has a better capability than choosing DNA plasmid as the booster to evoke memory B cells [16] . The inactivated vaccine as a booster is also considered to be able to balance the Th1 and Th2 immune responses [10] , which could enhance both specific cell-mediated immunity and neutralizing antibody inductions with increased T cell response. In the current study, the DNA vaccine stimulated a relatively strong IBV-specific cellular response but low antibody titers. When the DNA vaccine and inactivated vaccine were administered in combination, both higher cellular proliferation rates and antibody titers were observed among the DNA vaccine-primed chickens as seen in previous studies [10] . Chickens that received the DNA vaccine with the inactivated vaccine were fully protected from IBVSX16 challenge. None of these animals developed clinical signs or harbored detectable levels of virus in the trachea or kidney after challenge. These results clearly demonstrate that only the combined administration of DNA vaccine and inactivated vaccine, but not either alone, offered full protection from challenge with the IBVSX16 strain.