Since mosquito season often runs through October in the Midwest and nearly year-round down South, you might wonder when it’s best to vaccinate your horse against mosquito-borne diseases.

These are serious, sometimes fatal diseases like West Nile Virus, or WNV, and Eastern Equine Encephalitis [ĕn-sĕf-uh-LĪ-tus], or EEE. Vaccines developed against both are very effective in helping to prevent infection.

For previously unvaccinated horses, an initial series of two vaccinations is given over four to six weeks. The label recommendation for most vaccines is to booster annually, prior to the mosquito season. For horses at high risk, veterinarians recommend boosters every 4-6 months. Research indicates horses under 5 years or over 15 years of age have a higher risk of disease, especially in areas with year-round mosquito seasons.