Equine Vaccines Move Into The 21st Century

In the year 1798, Edward Jenner discovered that deliberately injecting healthy patients with material from a patient with cow-pox could protect them from getting smallpox. Unfortunately, they often got very ill, and his contention that this odd practice could protect against smallpox was not widely accepted.

In 1879, Louis Pasteur discovered that injecting chickens will an old, weakened culture of the bacteria that causes fowl cholera protected them. A Pasteur Anthrax vaccine followed in 1881.

This foal’s vaccine needs differ from those of a mature horse. Many horseowners do their own vaccinations, but you need to know what you’re giving, how often to give it, why you’re giving it, and what to do if there’s a reaction. How often your horse comes in contact with new horses helps you decide what vaccines to give. Shipping can be stressful for your horse, so vaccinate a few weeks before he travels.

In 1885, Pasteur successfully prevented rabies after vaccinating animals with a vaccine made from dried nervous system tissue from dogs that had rabies, and saved the life of a nine-year-old boy bitten by a rabid animal by giving him a series of injections of the rabies vaccine basically the same protocol that is still used today.

Building on these discoveries, many researchers began to come out with techniques for vaccines to protect from a wide variety of diseases. The pros far outweighed the cons, but side effects and reactions to these still crude vaccines were significant. With the advent of killed vaccines, serious side effects dropped considerably. Unfortunately, the protection provided by the killed vaccines is often inferior.

Human vaccine development moved on to uncover better ways to change organisms so that they were still alive but had little or no potential to produce disease and still generated a strong immune response. The next big breakthrough was to inoculate with only key pieces of the DNA of an organism. One of these technologies employs ”chimeras,” which take pieces of the DNA from organisms you’re interested in protecting against, incorporating them into the DNA of another organism that will not produce disease in the target species. The ”carrier” organism takes this DNA into the cells and generates a strong immune response.

While many modern, successful modified live or genetic-material vaccines made their way into small-animal medicine, for a long time most vaccines available for horses were the killed vaccines, which provide only limited protection for many diseases.

A notable exception was Pfizer’s Rhinomune, a modified live EHV-1 vaccine that was recently shown in one experiment to provide superior protection against the neuropathogenic strain of EHV-1/Herpes, aka Rhinopneumonitis (see neurological Herpes story on page 17). Two other innovative vaccines are the intranasal influenza and intranasal strangles, which use modified live organisms and stimulate protective immunity where the horse needs it the most, along his respiratory tract.

Most exciting of all are three new vaccines within the past two years. Merial’s Recombitek West Nile vaccine uses canarypox virus to carry West Nile DNA into the cells. Merial has also introduced a Recombitek Influenza vaccine, offering strong protection on a bodywide basis.

The newest addition is Intervet’s PreveNile, another chimera DNA vaccine that requires only one injection and begins to protect in as short a time as two weeks. We’re impressed with these manufacturers for working to bring equine vaccines into the 21st century.


Choosing Vaccinations

Our sidebar ”Equine Diseases with Available Vaccines” is a list of diseases for which vaccines are available. Compare that with our list of available vaccines, by brand (chart is in alphabetical order by vaccine name) and our chart on recommended vaccines by horse type.

It’s neither necessary nor advisable to vaccinate your horse against each and every disease out there. Many things should enter into your choice of vaccines, particularly the risk of exposure. Virtually anyone would think it’s ridiculous to vaccinate a horse in this country for a disease only present on some remote island, but it’s equally silly to vaccinate for American diseases the horse is unlikely to be exposed to. For example, horses living in the Arizona desert don’t have to worry about Potomac Horse Fever.


Your horse’s level of exposure to insect vectors or horses carrying diseases that spread by direct contact is also important to consider.

If your horse does a lot of traveling, or lives with horses that do, you might want to consider something like an influenza vaccine, but if he’s basically isolated from horses that move around a good bit, the risk of exposure is extremely low.

A history of bad reactions to vaccines may also influence your decision, and check out our list of when you should never vaccinate. In some instances, the effectiveness of an individual vaccine is so questionable it makes little sense to even consider it. Veterinarians are becoming much more sensitive to issues concerning vaccination and less likely to inundate every horse with each vaccine out there. Use our table for guidance, then discuss your individual vaccination needs with your vet.

Bottom Line

Based on published studies, we think the following vaccines are stand-outs:

Rhinopneumonitis/Herpes: Rhinomune.

Routine vaccination of adult, nonbreeding stock is usually unnecessary and is currently controversial because of the suspicion that this practice may have increased the prevalence of the neuropathogenic form. However, if you do need to vaccinate your horse because of high risk of exposure, especially the neuropathogenic form, this is the only vaccine that may provide some protection from that strain.


Influenza: Recombitek Influenza. FluAver I.N. Calvenza EIV.

Strangles: Pinnacle I.N.

While some problems have occurred with local vaccine reactions that mimic strangles, the protection from this vaccine against the disease is strong and the local reactions aren’t as serious as local or systemic reactions to the intramuscular vaccine.

West Nile: PreveNile. Recombitek West Nile.

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