Infectious bursal disease virus (IBDV), the causative agent of infectious bursal disease (IBD), causes immunosuppression in young chickens by destroying the precursors of B lymphocytes in the bursa of Fabricius. In recent years, antigenic variant IBDV strains and very virulent IBDV strains (vvIBDV) have been emerging and caused considerable economic losses to the poultry industry around the world. The traditional inactivated or attenuated vaccines could not provide enough protection against these variants a...