Animal coronavirus vaccines: lessons for SARS

Severe acute respiratory syndrome (SARS) emerged in China and spread globally as a human pandemic. It is caused by a new coronavirus (CoV) of suspect animal origin. The emergence of SARS stunned medical scientists, but veterinary virologists had previously recognized CoVs as causing fatal respiratory or enteric disease in animals with interspecies transmission and wildlife reservoirs. Because of its public health impact, major efforts are focused on development of SARS vaccines. Occurrence of CoV disease at mucosal surfaces necessitates the stimulation of local immunity, having an impact on the vaccine type, delivery and adjuvant needed to achieve mucosal immunity. Such immunity is often short-lived, requires frequent boosting and may not prevent re-infection, all factors complicating CoV vaccine design. SARS vaccine efforts should be enhanced by understanding the correlates of protection and reasons for the success or failure of animal CoV vaccines. This review will focus on studies of immunity and protection in swine to the enteric CoV, transmissible gastroenteritis (TGEV) versus the respiratory variant, porcine respiratory CoV (PRCV), comparing live, inactivated and subunit vaccines, various vaccine vectors, routes and adjuvants. In addition avian infectious bronchitis CoV (IBV) vaccines targeted for protection of the upper respiratory tract of chickens are discussed. Unfortunately, despite long-term efforts, effective vaccines to prevent enteric CoV infections remain elusive, and generally live, but not killed vaccines, have induced the most consistent protection against animal CoVs. Confirmation of the pathogenesis of SARS in humans or animals models that mimic SARS may further aid in vaccine design and evaluation.