What to Expect When Vaccinating

Here's what you need to know about possible reactions to standard vaccinations.


When vaccination time rolls around, do you know what to expect after your horse’s immunizations? Every horse owner expects their vaccinated horse to be protected from disease, but some horse owners don’t expect to see a reaction that may occur after a vaccination.

“Vaccines can save time, money and may even save your horse’s life,” says April Knudson, DVM, manager, Veterinary Services, Merial. “Understanding the risk from vaccination can probably save you a few hours of worrying, but it’s important to remember that the reaction to any vaccine is likely far less devastating than if your horse actually acquired the disease you vaccinated for.”1

Vaccines are designed to stimulate an immune response, notes Dr. Knudson. Each horse is unique — and a horse’s specific immune response may be different from other horses.2

In particular, Dr. Knudson says that it’s fairly common for horses to experience mild, temporary side effects a few hours after intramuscular vaccination, such as:3

  • Local muscle soreness or swelling
  • Fever
  • Loss of appetite
  • Lack of energy or alertness

Even humans experience signs like this following vaccinations,” Dr. Knudson says. “What happens to the immune system after vaccinations can’t always be seen, but these types of clinical signs help demonstrate that an immune response has been stimulated – which is exactly what we want the vaccine to do.”

However, Dr. Knudson recommends contacting your veterinarian immediately if any of these signs persist for more than 24 hours or if more serious side effects, such as hives, difficulty breathing, collapse or colic occur. These more serious side effects are rare.3,4

Getting your local veterinarian involved is the best way to ensure horses are being vaccinated for the area’s disease risks, and make certain the vaccines themselves are handled and administered properly. Vaccines that are handled improperly can become ineffective or may actually increase the risk of side effects.2,5

In addition, vaccination time is a great opportunity to make certain all aspects of an equine health care regimen are up-to-date with current disease threats, Dr. Knudson recommends.

“Vaccinations are a vital part of any equine health program,” Dr. Knudson says. “A good rule of thumb is to check with your veterinarian at least twice a year — usually in the spring and fall — to make sure horses are receiving vaccinations in alignment with the region’s disease risks and the horse’s travel schedule. Plus, it’s a good time to make sure nutritional and dental needs are being met and deworming programs are on track.

“Veterinarians are the best source for quality vaccines and vaccination information, and checking in a couple times a year helps make sure your horse is healthy year-round.”

1 MacAllister C, Gilliam L. Equine vaccination programs. Oklahoma Cooperative Extension Service Publication VTMD-9119. Available at: /redirect.php?location=http%3a%2f%2fpods.dasnr.okstate.edu%2fdocushare%2fdsweb%2fGet%2fDocument-2072%2fVTMD-9119web.pdf. Accessed December 5, 2008.

2 Merck Veterinary Manual. Ninth edition. 2005:2181.

3 Adverse reactions. American Association of Equine Practitioners. Available at: /redirect.php?location=http%3a%2f%2fwww.aaep.org%2fadverse_reactions.htm. Accessed December 5, 2008.

4 Povey RC and Carman PS (Martinod S). Technical basics of vaccination. In: Pastoret PP, Blancou J, Vannier P, Verschueren C, eds. Veterinary Vaccinology. New York: Elsevier; 1997;15:574-578.

5 Merck/Merial Manual for Pet Health. Home edition. 2007:561.


  1. I have a 8 year old mare that has a serious reaction every time she recieves her flu/rhino shot. she has difficulty breathing, fever,symptoms of shock and it lasts for several days to over a week last time so I have ommitted that vaccine and only give her west nile, eee=wee/tetenus and only once in the spring. I have given her the internazel Flu/rhino with no problems. Could it be the carrier as both the west nile and the flu/rhino she did have reactions to are supplied by Fort Dodge. I have heard that the “carrier” in both could be the culprit. I really do need to keep her current. Any suggestions?


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