Equine Vaccines: Breaking Down the Basics

What is a standard vaccination program for horses?

It would be convenient to have a one-size-fits-all, black and white schedule for equine vaccinations. However, as we all know, horses are individuals (and rarely concerned with what’s convenient), which results in a lot of gray areas. As such, there is no standard equine vaccination program. The need for specific vaccines depends on many factors, including risk of disease, horse age, location, and if they travel. It is important to weigh the consequences and costs of each specific disease against the costs of vaccination and potential vaccine reactions.

The American Association of Equine Practitioners (AAEP) provides guidelines for a set of core vaccines, which are “vaccinations that protect from diseases endemic to a region, those with potential public health significance, required by law, virulent/highly infectious, and/or those posing a risk of severe disease. Core vaccines have clearly demonstrated efficacy and safety, and thus exhibit a high enough level of patient benefit and low enough level of risk to justify their use in the majority of patients.” Equine vaccines that meet these criteria are for Eastern/Western equine encephalomyelitis (EEE, WEE), rabies, tetanus, and West Nile virus (WNV).

Other available equine vaccines are “risk-based vaccines”. These include equine herpesvirus (rhinopneumonitis, or “rhino”, specifically EHV-1 or EHV-4), equine influenza, strangles, and others.

Organizations, venues and boarding facilities may require some of these vaccines prior to entry or competition.

Why is it important to monitor my horse after a vaccination?

Horse owners, barn managers, and other caretakers should be aware of possible vaccine reactions. While mild, often localized, reactions are not uncommon, severe, systemic reactions are fortunately extremely rare. Monitor your horse(s) for at least 72 hours after any vaccination so you and your veterinarian can respond promptly to any complications.

Potential adverse reactions depend on a number of factors, including the route of vaccine administration (intramuscular (IM) or intranasal (IN)). Local reactions, such as muscle soreness and swelling, or the formation of an abscess around the injection site, can occur. Some horses may exhibit a mild fever, which can contribute to inappetance and lethargy. In other words, your horse may not feel like themselves the day after a vaccination and it is often advisable to avoid any strenuous exercise, including riding (handwalking is usually okay).

Systemic reactions occur throughout the body and are not restricted to the administration site. These can include hives, colic, swelling of the limbs and abdomen (purpura hemorrhagica), difficulty breathing, and anaphylaxis.

Although mild reactions often resolve on their own, all adverse reactions should be reported to your veterinarian who will share pertinent information with the vaccine manufacturer and/or the United States Department of Agriculture (USDA) Center for Veterinary Biologics. Since adverse reactions may be unpredictable, it is recommended to avoid vaccinations within two to three weeks of a competition, sale, or travel to ensure time for treatment, should the need arise.

Does my horse have to be vaccinated every year? What happens if my horse misses a year of vaccinations?

As with many questions about equine vaccines, the need for a horse to be vaccinated every year should be evaluated on a case-by-case basis. The answer depends on the risk that the horse will come in contact with that particular pathogen. Is the disease common to that specific location? Is it a vector-borne (i.e. transmitted by another animal or insect) disease that depends on seasonal activity of mosquitoes or other insects? Does the horse travel for competitions? Does the horse live near other horses that travel frequently? How contagious is the pathogen? Some vaccines are more effective than others, which also factors into the overall equation.

The implications of a horse missing a year of vaccinations depends on the immunization history of that animal. The lapse can have more significant consequences if it is during the primary course of vaccinations for young or naïve horses that have not yet mounted optimal immune responses, whereas it may be less significant in adults that have otherwise been routinely vaccinated.