Horse Side Vet Guide ®

Equine Health Resource

Vaccination Reaction

Vaccination reactions are fairly common in horses, and usually result in local swelling, soreness, reduced appetite and depressed attitude.

Less common but more severe allergic reactions to vaccines may result in hives full-blown body-wide anaphylaxis, which develop suddenly and can be life threatening. Blood pressure can drop dramatically. Horses can have trouble breathing or have diarrhea or colic. Usually, rapid treatment is needed in order to save the horse.

New vaccines are tested to reduce adverse reactions but there is always a possibility of reaction. If a horse has reacted once to a vaccine, the reaction could be more serious the next time. Your vet will keep a record of this reaction to prevent similar problems in the future. They may discuss vaccine alternatives with you. If the reaction is severe, they may discuss the problem with the vaccine manufacturer.

Prognosis & Relevant Factors

The prognosis for simple local inflammatory types of reactions is good. The prognosis for full-blow anaphylactic allergic reaction is always guarded, as they often require immediate and appropriate treatment.


  • Does the fact that the horse reacted this time mean it cannot be vaccinated for that disease again?
  • Can the horse be "pre-treated" with an anti-inflammatory to reduce overreaction to the vaccine?
  • Can a different brand of vaccine be used, possibly with a different carrier?
  • Since the horse has reacted to a vaccine intended to immunize for several diseases, can these be broken up into separate shots for each disease?

    If a horse has a reaction to a vaccine, consider changing the vaccine type or pretreat with an anti-inflammatory before administering again.

    Have your vet vaccinate your horse instead of doing it on your own.

    Author: Doug Thal DVM Dipl. ABVP


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