Equine Vaccinations

Horses, like other animals, are routinely vaccinated against illnesses that may make them gravely ill. To a certain extent, specific immunizations are administered according to the judgement of the the particular equine veterinarian, depending on the doctor's assessment of risk factors such as age, geographic location, and possible exposure. The American Association of Equine Practitioners (AAEP), however, defines certain vaccinations as core vaccinations for all horses in the United States.

Core Equine Vaccinations

The assessment of the AAEP is based on the evaluation of certain diseases as especially infectious, virulent, endemic to particular regions or posing a high degree of risk to public health. Some of these vaccinations are also required by law. All of them have been found to be beneficial with a very low level of patient risk.

Equine Encephalomyelitis

There are two types of equine encephalomyelitis: eastern (EEE), western (WEE). Although some horses develop asymptomatic cases of encephalomyelitis resulting in immunity, EEE and WEE are extremely serious diseases. The Eastern type is most dangerous, having a mortality rate of almost 90 percent.


Rabies is rarely contracted by horses, but when it is, it invariably results in fatal encephalitis. Horses contract the illness through the bite of a wild animal, such as a raccoon, fox, bat or skunk. It passes from the saliva of the infected animal into the open wound, attacking neural tissue. Neurological symptoms, including convulsions and paralysis occur and the animal dies within 1 to 5 days.


Tetanus is caused by a common bacteria present in the gastrointestinal tracts and feces of horses and other animals. It is a serious, often fatal, disease. Although any wound is susceptible to infection with the bacteria, tetanus most often develops in a puncture wound or a reproductive tear. While it can be treated with antibiotics, many animals die of complications of this illness.

West Nile Virus

West Nile virus, like EEE and WEE, is transmitted by mosquitoes who usually pick it up from wild birds. The illness is fatal in approximately 35 percent of infected horses and is the leading cause of encephalitis in horses in the United States. Even in horses that recover from the disease, close to 50 percent still show residual damage after 6 months.

Core vaccinations are given to horses on a schedule determined by the veterinarian. In most cases, they offer complete protection against the targeted disease.

Risk-Based Vaccinations

Veterinarians may recommend other vaccinations depending on their assessment of the individual horse's risk factors. Non-core vaccinations may be administered for the following illnesses:

  • Rhinopneumonitis (Equine herpes virus)
  • Equine influenza
  • Potomac horse fever
  • Botulism
  • Strangles

Horses' risks of contracting these illnesses are based on geographic region, travel expectations, potential exposure to other horses, age, gender, breeding status and general health.

Side Effects of Vaccinations

As with all medical treatments and procedures, there is some small element of risk associated with the administration of equine vaccinations. For the most part, any adverse effects are localized and of limited duration. These include muscle swelling or stiffness, low-grade fever, loss of appetite and lethargy and are most frequently associated with the influenza inoculation.

Rarely, more serious side effects occur, including anaphylaxis, a life-threatening allergic reaction. Analphylaxis can be combatted with epinephrine if treated immediately.

Because of the possibility of side effects, it is recommended that horses do not receive any vaccinations within 2 weeks of any stressful situation, such as a performance, change of ownership, or shipment to another location.

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