Comparative Evaluation of Immune Responses and Protection of Chitosan Nanoparticles and Oil-Emulsion Adjuvants in Avian Coronavirus Inactivated Vaccines in Chickens

Efficient vaccines are the main strategy to control the avian coronavirus (AvCoV), although several drawbacks related to traditional attenuated and inactivated vaccines have been reported. These counterpoints highlight the importance of developing new alternative vaccines against AvCoV, especially those able to induce long-lasting immune responses. This study evaluated and compared two inactivated vaccines formulated with AvCoV BR-I variants, one composed of chitosan nanoparticles (AvCoV-CS) and the second by Montanide oily adjuvant (AvCoV-O). Both developed vaccines were administered in a single dose or associated with the traditional Mass attenuated vaccine. The AvCoV-CS vaccine administered alone or associated with the Mass vaccine was able to induce strong humoral and cell-mediated immune (CMI) responses and complete protection against IBV virulent infection, wherein single administration was characterized by high IgA antibody levels in the mucosa, whereas when associated with the Mass vaccine, the serum IgG antibody was predominantly observed. On the other hand, single administration of the oily vaccine presented poor humoral and CMI responses and consequently incomplete protection against virulent challenge, but when associated with the Mass vaccine, immune responses were developed, and complete protection against infection was observed. Both of our experimental vaccines were able to induce full protection against virulent IBV challenge. A single dose of AvCoV-CS vaccine was sufficient to achieve complete protection, while AvCoV-O required a previous priming by a Mass strain to complete the protection.