Comparison of oil emulsion, mannosylated chitosan, and Bacillus vector adjuvants for vaccination against influenza in chickens

Vaccination against influenza continues to be the primary method of control in many countries, but there is still a strong reliance on autogenous vaccines adjuvated with mineral oil emulsions known to induce overly high local inflammatory responses and lesions at the site of injection. The studies presented herein investigate various combinations of mannosylated chitosan adjuvant (MCA) and/or recombinant Bacillus construct adjuvant (BCA) containing highly conserved influenza antigens to assess their ability to function as an effective alternative adjuvant in influenza vaccination. In experiment 1, broilers were vaccinated via subcutaneous and/or drinking water application with an inactivated swine influenza in combination with MCA or commercial oil emulsion adjuvant. Subcutaneous or oral prime, followed by oral boost, resulted in the highest improvement in day 21 serum IgG hemagglutination inhibition (HI) titer, compared to the non-vaccinated control group. Experiment 2 tested BCA and MCA adjuvants, mixed with inactivated avian influenza virus in broilers. The group receiving combined subcutaneous and oral prime, followed by an oral boost containing both MCA and BCA adjuvants, exhibited significantly improved tracheal IgA HI titers. Experiment 3 investigated the ability of these adjuvated vaccines to protect against both homologous and heterologous highly pathogenic avian influenza challenge in layers. Groups receiving a subcutaneous prime followed by either subcutaneous or oral boost survived at 100%. Groups receiving only oral vaccine administrations did not exhibit improved survival. MCA and BCA adjuvants were found to improve immune responses in both broiler and layer-type chickens, equivalently matching immunogenicity and protection to the traditional mineral oil emulsion adjuvant. These studies suggest protective mucosal immunity can be achieved with vaccination strategies that incorporate MCA or BCA, but primary parenteral administration remains an important component of the vaccination strategy to achieve protective immunity.