A DNA Prime and MVA Boost Strategy Provides a Robust Immunity against Infectious Bronchitis Virus in Chickens

Infectious bronchitis (IB) is an acute respiratory disease of chickens caused by the avian coronavirus Infectious Bronchitis Virus (IBV). Modified Live Virus (MLV) vaccines used commercially can revert to virulence in the field, recombine with circulating serotypes, and cause tissue damage in vaccinated birds. Previously, we showed that a mucosal adjuvant system, QuilA-loaded Chitosan (QAC) nanoparticles encapsulating plasmid vaccine encoding for IBV nucleocapsid (N), is protective against IBV. Herein, we report a heterologous vaccination strategy against IBV, where QAC-encapsulated plasmid immunization is followed by Modified Vaccinia Ankara (MVA) immunization, both expressing the same IBV-N antigen. This strategy led to the initiation of robust T-cell responses. Birds immunized with the heterologous vaccine strategy had reduced clinical severity and >two-fold reduction in viral burden in lachrymal fluid and tracheal swabs post-challenge compared to priming and boosting with the MVA-vectored vaccine alone. The outcomes of this study indicate that the heterologous vaccine platform is more immunogenic and protective than a homologous MVA prime/boost vaccination strategy.