Merck Prestige 3 + WNV is an effective vaccine for Eastern and Western encephalomyelitis, tetanus and West Nile virus in horses. Tetanus, WNV, EEE and WEE are core vaccinations recommended by the AAEP vaccine guidelines and are indicated in the immunization program for all horses each year. West Nile virus (WNV) is the leading cause of arbovirus encephalitis in horses and humans in the United States. For primary vaccination aseptically administer 1 mL intramuscularly, repeat with a single dose in 3 – 4 weeks. Historically, annual revaccination with this product has been recommended. The need for this booster has not been established. The presence of maternal antibody is known to interfere with the development of active immunity in foals and additional boosters will be required in most young animals. For more information on revaccination frequency, consult your veterinarian.