Characterisation of adjuvants for use in dromedary immunisation

Although camelids are an important domestic species with more than 25 million members, little is known about vaccine adjuvant efficacy, safety and mechanism of action in this species. This presents a major problem for design of effective camelid vaccines. This is of more than theoretical interest given the recent emergence of. camels as vectors of transmission to humans of lethal viral diseases such as Middle Eastern Respiratory Syndrome (MERS) coronavirus. Hence availability of well-validated camelid vaccine adjuvants may be important not just for vaccines to prevent diseases of camels but also to block their ability to transmit disease to humans. In this study, we used dromedaries to test the safety and efficacy of four different adjuvant formulations (Advax™ HCXL, Advax AF-1, Advax AF-2 or alum) together with four different antigen formulations (B. mallei, C. pseudotuberculosis, C. perfringens, Rhinovirus) administered by subcutaneous injection in the neck region of adult animals. All the Advax delta inulin-based adjuvants and the alum adjuvant were well tolerated, with no severe lesions such as the draining granulomas that are caused by oil emulsion adjuvants. There was no trend for increased vaccine reactogenicity in camels that had existing immunity to the vaccine antigens. Overall, the vaccines had modest immunogenicity in these adult animals indicating the need for further research to identify the optimal adjuvant formulation, dose and immunisation route for camelid vaccines.