Shot Spots

All in all, vaccine reactions are very rare, and the process of vaccination against a disease process is one of the best ways you can safeguard your horse's health. Vaccination is one of the most impressive discoveries of modern medicine; the ability to protect a horse against the ill effects of several severe and often fatal diseases is a huge benefit. However, you should understand the risks, and discuss potential reactions beforehand with your veterinarian, in case your horse is one of the few who suffer from a reaction.

Local Vaccine Reactions

Vaccines can sometimes cause local reactions and even some systemic effects. The most common reaction (RXN is the medical abbreviation) to a vaccination is most likely to be a simple stiff neck. Generally, the neck soreness does not cause a problem and will resolve on its own in a few days. Where it does cause a problem is if you are unaware that it can happen and vaccinate on Wednesday or Thursday and think you are going to a show on Saturday, only to find out that the horse won't bend or move his neck very well. If a lump forms or the muscle around the injection site becomes very hard, you can use a cold pack and administer oral phenylbutazone (Bute). If the swelling does not subside after a few days, the area can be hot-packed with a hot towel (placing a hot bran mash inside a Ziploc bag works very well for hot-packing) four to six times per day for 10-15 minutes each time.

As many of you might have experienced with the human flu vaccine, it is not uncommon to spend a day or two of "not feeling quite right" after receiving a vaccination. Horses are no different and can become slightly depressed or develop a poor appetite for 24-48 hours after vaccination. The important thing is that they should not develop a significantly abnormal temperature (up to 101.5°F can be caused by vaccine stimulus, but a higher fever should be evaluated further), or abnormal heart or respiratory rate. If the vital signs are abnormal or the mild depression/inappetence continues for more than 48 hours, the horse should be examined by a veterinarian.

It is extremely rare for an abscess to form at the site of a vaccine injection, but it does happen. These are often just sterile inflammatory reactions to the vaccine (there is no infection) and might or might not burst through the skin and drain. There is also the possibility of infection being the cause of the reaction (and abscess formation). In some cases, contamination from something on the skin can occur as the needle punctures the skin, causing the horse to have an adverse reaction. Either type of abscess might require a veterinarian to "lance" the skin to facilitate drainage. If these horses are showing any signs of depression, loss of appetite, fever, or elevated heart rate/respiratory rate, they should be seen by a veterinarian as soon as possible.

Another sign of a more serious infection is the presence of air under the skin. Some types of bacteria produce gas that collects under the skin. You can feel this as a crackle-type feeling, almost as if there were bubble-wrap packing material under the skin. If you feel this and the horse is acting sick, it constitutes a veterinary emergency.

More Severe Reactions

Have you ever wondered why your physician makes you sit in the office for those eternal 20 minutes after getting a vaccination? It is so you don't die from an anaphylactic (allergic) reaction on the drive home.

The odds of an anaphylactic reaction happening is about 1:1,000,000 (about the same risk as your horse being struck by lightning); however, it is serious if your horse is affected. The development of anaphylactic shock following vaccination for almost any disease process can occur and is listed as a potential complication on the package insert of most vaccine products. This is something to take seriously. If your horse is the unlucky 1:1,000,000, he will most likely die if treatment is not available immediately.

For those of you who have your veterinarian perform your vaccinations, there is generally less risk as the veterinarian can immediately treat shock if it occurs. But if you're in the ever-growing population of "self-vaccinators" due to the availability of "over-the-counter" equine vaccines and the desire to save some money, you could experience a horrible tragedy someday.

I'm not an advocate of "self-vaccination," but I know this is a touchy subject. To me, it is playing Russian roulette with your horse's life. So if you are going to give your own vaccinations, at least be aware of the potential complications and consult with your veterinarian regarding what treatments to have on hand and what to do with them should an anaphylactic reaction occur.

Keep in mind that drugs, in addition to vaccines, can cause anaphylaxis. Many think that anaphylaxis is an immediate reaction, but it can actually happen 15-20 minutes after exposure to the trigger. The clinical signs to watch for are listed below.

If anaphylaxis is severe and allowed to progress, the animal or person dies from severely low blood pressure and massive fluid accumulation in the lungs in a very short period of time. The drug epinephrine is considered to be life-saving due to its effects on heart rate and blood pressure.

Take-Home Message

Some horses will have mild reactions to their vaccinations, but in weighing those in the balance of life-threatening illness, the odds are in your favor when you protect your horse with proper vaccinations. If you decide to vaccinate your horses yourself, make sure to have your veterinarian teach you proper techniques and what to do in case of a severe reaction.

About the Author

Michael Ball, DVM

Michael A. Ball, DVM, completed an internship in medicine and surgery and an internship in anesthesia at the University of Georgia in 1994, a residency in internal medicine, and graduate work in pharmacology at Cornell University in 1997, and was on staff at Cornell before starting Early Winter Equine Medicine & Surgery located in Ithaca, N.Y. He is also an FEI veterinarian and works internationally with the United States Equestrian Team.

Ball authored Understanding The Equine Eye, Understanding Basic Horse Care, and Understanding Equine First Aid, published by Eclipse Press and available at or by calling 800/582-5604.

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