For intramuscular vaccination of healthy horses 10 months of age or older as an aid in the prevention of viremia caused by West Nile virus, and as an aid in the prevention of equine encephalomyelitis due to Eastern and Western viruses, and tetanus. Efficacy of the West Nile fraction was demonstrated in horses that received two doses of the vaccine and were challenged one year post-vaccination with West Nile virus. The vaccine protected 95% of the vaccinates against infection, while 82% of the controls were viremic.