has role immunizes recipient immunizes against pathogen Eastern equine encephalitis virus Western equine encephalitis virus Clostridium Equus caballus vaccine toxoid vaccine bacterial and viral combination vaccine Clostridium vaccine toxoid vaccine role horse vaccine Eastern Equine Encephalitis Virus vaccine equine EEV and WEV encephalomyelitis vaccine-tetanus toxoid Asiyah Yu Lin vaccine Oliver He Western equine encephalomyelitis virus vaccine