Equine Vaccines: Some Specifics

What are the advantages of having a veterinarian vaccinate my horse?

It is recommended to have a veterinarian vaccinate your horse, instead of doing it yourself, for several reasons.

• Vaccines must be procured from reliable sources that can verify proper storage. Poor quality, contamination, and storage at the wrong temperature can reduce efficacy and increase risks of adverse reactions.
• It is critical to ensure proper dosing to maximize immunity and protect against vaccine failure. Some competitions require vaccines to be administered and documented by a licensed veterinarian. (See sidebar)
• Adverse reactions can be unpredictable. Although severe reactions are rare, prompt treatment is often required.
• Many manufacturers guarantee support, including coverage of treatment costs, only if the vaccine was administered by a veterinarian.
• Veterinarians usually perform physical examinations to ensure the horse is healthy enough for vaccination. If your horse has a mild fever, for example, vaccination should be postponed. These visits are also good opportunities to ask questions and assess your horse’s overall health.

When should I consider spacing out vaccinations?

It is important to properly vaccinate your horse, but it may be inadvisable to hit them with everything at once.

Many horses are unfazed by receiving several vaccines at the same time. This includes multi-way (multivalent) vaccines that protect against more than one pathogen. Horses with histories of adverse reactions, or those that are immunocompromised may benefit from time between vaccinations.

Administering multiple vaccines at once may increase the risk of adverse reactions. Veterinarians may recommend a three to four week interval between immunizations (another important reason to plan around travel and competitions). Non-steroidal anti-inflammatories (NSAIDs) may be recommended prior to vaccination, but this should be discussed with your veterinarian to ensure that medications will not affect the vaccine’s efficacy or result in health concerns.

Can my horse be tested for antibodies to determine if vaccination is needed?

Recently, the idea of “checking titers” to determine if a horse needs to be vaccinated has become popular. Although this sounds straightforward, the correlation between protection and serological response to vaccination has not been well established for most equine vaccine antigens.

Serological testing to determine levels of circulating antibodies (a.k.a. titers) to specific pathogens may be used when potential adverse reactions pose greater risks than consequences from disease or to assess potential non-responders (immunodeficient, diagnosed with pituitary pars intermedia dysfunction, etc.).

However, it is important to remember that circulating antibodies are only part of the immune response. Immune responses can occur throughout the body, as evidenced by pathogen-specific antibodies in the blood, or locally, in which antibodies may remain in particular areas of the body and not be present in the bloodstream. As such, there are limitations to evaluating titers with respect to specific pathogens. The correlation depends on the specific disease, the route of vaccine administration, the type of vaccine, and the strength of the immune response. Titers correlate well with protection or susceptibility for some pathogens (tetanus, rabies), but cannot be easily quantified for others (WNV, equine influenza).

The AAEP’s “Guidelines for Serology in Horses with Adverse Events from Vaccination” provides more information.

Is it OK to change vaccine manufacturers?

It is unlikely that horses will receive the same vaccine products regularly throughout their lives, for many reasons (change of ownership, location, vaccine shortage, etc.). Products from different manufacturers are regularly used interchangeably. To date, research of impacts on immune response and subsequent protection is sparse.

The number of possible vaccine combinations is large, so it is difficult to provide conclusions for particular products. The answer essentially depends on how different or similar vaccines are to one another. In some cases, utilizing different products may induce a superior immune response. However, there are many factors to take into consideration, such as the age of the horse and time since last immunization.

UC Davis researchers reported results of a Center for Equine Health supported study that investigated immune response to equine influenza virus vaccines from different manufacturers in previously immunized, healthy, adult horses. The data showed similar antibody responses across groups, even after a booster, suggesting the specific equine influenza vaccine manufacturer should not be a primary concern.

Vaccination Requirements for Competition

American Quarter Horse Association (AQHA) – Vaccination for equine influenza and EHV are required for AQHA championship shows. Details are provided on resources pages for individual shows.

Fédération Equestre Internationale (FEI) – A veterinarian must administer the influenza vaccine within six months (but not less than seven days) of arrival at event sites. (Articles 1002 and 1003)

United States Equestrian Federation (USEF) – Horses over 7 months of age must receive EHV and influenza vaccines within six months of entering competition grounds. It is recommended that vaccines be administered by a veterinarian. (Rule GR845)

*Venues may require proof of vaccination prior to arrival or competition for unrated events.