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Preventive Medicine

“The best defense is a good offense” when it comes to disease prevention.

Drawing from the old cliché, a horse’s best defense against infectious disease is immunization. Horses are vaccinated against a whole alphabet soup of diseases, including EEE, WEE, rabies, tetanus, rhinopneumonitis, influenza, PHF, West Nile virus and strangles.

Immunization begins when horses are foals. The first time a foal receives a vaccine, its system mounts an immune response to substances in the vaccine called “antigens.” Antigens are similar or identical to the proteins expressed by the disease organism, but modified or inactivated so as to not cause illness and tested for safety and efficacy. Once the initial series of injections is given, immunizations are repeated several weeks later in order to boost the immune response and stimulate full protection. Thereafter, most vaccines are administered at yearly intervals to keep the horse’s system primed. Vaccines against the viral respiratory diseases frequently passed on at horse shows, racetracks, and large stables are usually given several times a year to horses that travel and compete. Most vaccines are given via intramuscular injections, while those for influenza and strangles can be given intranasally or via injection.

The scientific community has been taking a closer look at the timing of vaccinations for horses. The American Association of Equine Practitioners has assembled a committee to issue updated national recommendations on vaccine use. One of the committee’s experts is Dr. Wendy Vaala, who lectured on foals at the 1999 GVEC Horse Health Seminar. Dr. Vaala told us that the committee’s new vaccination schedule recommendations are as follows:

  • Initiate vaccination at six months of age rather than the traditional three months. This timing prompts the strongest response.
  • Administer a series of three vaccinations for most diseases (one initial vaccine and two boosters) at one-month intervals. Rabies immunization shows strong protection when given twice.
  • Influenza protection appears to work best if delayed until the foal reaches its yearling year. The intranasal flu vaccine does not require booster administration.


Recommendations on how frequently to administer vaccines to adult horses are still under development, and we will update you as new schedules become available. In the meantime, we are confident that the new schedule for this year’s foals will get our new crop off to a healthy start!