Equine Core Vaccines

by | May 18, 2026 | blog

Understanding Equine Core Vaccines

Source: the American Association of Equine Practitioners

Vaccination is one of the most important tools we have to protect the health and wellbeing of equines. However, not all vaccines are created equal. In veterinary medicine, vaccinations are generally divided into two categories: core and non-core.

Non-core vaccines are recommended based on a horse’s individual risk factors. For example, a show horse that travels frequently may require different vaccines than a pleasure horse that remains on the same property year-round.

Core vaccines, on the other hand, are considered essential for all horses, regardless of their lifestyle or travel schedule. A vaccine is classified as “core” based on several factors:

  • How easily and quickly the disease spreads
  • The severity of clinical symptoms
  • The fatality rate
  • Potential public health risks, including zoonotic diseases (diseases that can spread from animals to humans)

Core vaccines can vary somewhat by region depending on climate and disease prevalence. However, equine core vaccines are generally consistent across the continental United States. In warmer climates, the timing of vaccinations may shift slightly due to earlier mosquito activity.

The American Association of Equine Practitioners (AAEP) currently recommends four core vaccines for horses:

  • Tetanus
  • Eastern and Western Equine Encephalomyelitis (EEE/WEE)
  • West Nile Virus (WNV)
  • Rabies

While tetanus and rabies vaccines can be given year-round, the mosquito-borne diseases (EEE/WEE and West Nile) are typically administered before mosquito season begins. In Colorado, this is usually March or April.

Tetanus

Often called “lockjaw” because of the characteristic muscle stiffness it causes, tetanus is a serious disease caused by a toxin produced by the bacteria Clostridium tetani.

The bacteria naturally live in soil, and infection occurs when they enter the body through a wound. Horses are extremely sensitive to the toxin, and tetanus is frequently fatal in unvaccinated animals.

Although humans can also develop tetanus, the disease does not spread directly between animals and people, so it is not considered a zoonotic disease.

Tetanus Vaccination Schedule

Foals (Less than 1 Year)

  • For foals born to vaccinated mares:
    • First dose at 4-6 months old
    • Second dose 4-6 weeks later
    • Third dose at 10–12 months old
  • For foals born to unvaccinated mares, or mares with unknown history:
    • Start earlier (3–4 months of age) with the same three-dose structure as above

Adult Horses (Over 1 Year)

  • For vaccinated horses
    • Annual vaccination
    • Booster if injured 6 months or more after the last vaccine.
  • Unvaccinated horses or horses with unknown history:
  • Two-dose series, 4–6 weeks apart
  • Annual boosters thereafter

Broodmares

  • Previously vaccinated
    • Annual vaccination
    • Booster 4–6 weeks before foaling
  • Unvaccinated or unknown history
    • Two-dose series, 4–6 weeks apart
    • Booster 4–6 weeks before foaling

Eastern & Western Equine Encephalomyelitis (EEE/WEE)

Equine encephalomyelitis is often called “sleeping sickness” in horses because affected animals may appear severely depressed or unresponsive.

This viral disease is transmitted by mosquitoes. In North America, there are three forms:

  • Eastern Equine Encephalomyelitis (EEE)
  • Western Equine Encephalomyelitis (WEE)
  • Venezuelan Equine Encephalomyelitis (VEE)

Only EEE and WEE are considered core vaccines in the United States. The VEE vaccine is typically recommended only for horses traveling to Central or South America, where the virus is endemic.

Humans can also become infected through mosquito bites, but horses do not directly transmit the disease to people. However, cases in horses indicate that infected mosquitoes are present in the area.

EEE/WEE Vaccination Schedule

Foals

  • First dose at 4–6 months old
  • Second dose 4–6 weeks later
  • Booster at 10–12 months old, ideally before mosquito season

Adult Horses

  • Annual vaccination before mosquito season
  • Unvaccinated or unknown history
    • Two-dose series, 4–6 weeks apart
    • Booster 4–6 weeks before mosquito season
    • Annual boosters thereafter 

Broodmares

  • Vaccinated mares
    • Annual vaccination
    • Booster 4–6 weeks before foaling
  • Unvaccinated or unknown history
    • Two-dose series, 3–6 weeks apart
    • Booster 4–6 weeks before foaling or mosquito season (whichever is sooner)

West Nile Virus

West Nile Virus (WNV) is another mosquito-borne viral disease that can cause neurological illness in both horses and humans.

Like EEE/WEE, horses do not transmit the disease directly to humans, but infected horses signal that virus-carrying mosquitoes are present in the environment.

Vaccination is highly effective at preventing severe disease.

West Nile Vaccination Schedule

Foals

  • Born to vaccinated mares
    • First dose at 4-6 months old
    • Second dose 4–6 weeks later
    • Third dose at 10–12 months old
  • Born to unvaccinated mares or mares with unknown history
    • First dose at 3–4 months old
    • Second dose 3–4 weeks later
    • Third dose 8 weeks after the second dose (or sooner if mosquito season has begun)

Adult Horses

  • Annual vaccination before mosquito season
  • Unvaccinated or unknown history
    • Two-dose series spaced 3–6 weeks apart
    • Booster 4–6 weeks before mosquito season
    • Annual boosters thereafter

Broodmares

  • Previously vaccinated mares
    • Booster 4–6 weeks before foaling
  • Vaccination is not recommended during pregnancy for unvaccinated mares.

Rabies

Although rabies in horses is rare, vaccination is extremely important because there is no treatment, and the disease is fatal once symptoms appear.

Rabies is caused by a virus transmitted through the saliva of infected animals, most often through bites. Wildlife such as bats, skunks, raccoons, and foxes are common carriers.

Rabies poses a serious zoonotic risk, meaning it can spread easily from animals to humans and will cause fatal illness. Anyone who believes they or their animals may have been exposed should refer to the Colorado Department of Public Health and Environment for guidance on exposure protocols.

Rabies Vaccination Schedule

Foals

  • Born to vaccinated mares
    • First dose at 4–6 months old
    • Second dose 4–6 weeks later
    • Annual boosters thereafter
  • Born to unvaccinated mares or mares with unknown history
    • Single dose at 4–6 months old
    • Annual boosters thereafter

Adult Horses

  • Annual vaccination
  • Single dose for both vaccinated and unvaccinated horses.

Broodmares

  • Vaccinate 4–6 weeks before foaling
    or
  • Vaccinate before breeding

Core vaccines are a critical part of preventive health care for every horse, regardless of lifestyle or location. Diseases like tetanus, rabies, West Nile virus, and equine encephalomyelitis can spread quickly, cause severe illness, and in many cases prove fatal. Fortunately, routine vaccination provides safe and effective protection.

Working with your veterinarian to establish an appropriate vaccination schedule helps ensure your horse stays healthy while also protecting other animals and people in the community.