The Dreaded Vaccine Reaction

Written by University of Florida veterinary student, Allison Shingleton

In horses, vaccines are given intramuscularly, in the neck, once or twice per year. Rarely, adverse reactions can happen and lead to abnormal behaviors.

The most common type of reaction is a local reaction at the injection site. This includes swelling and pain/soreness around the area, and can sometimes lead to fever, and decreased appetite. If this occurs, your horse may be reluctant to lower its head or walk. Generally this occurs within 12-24 hours after the vaccine is administered. Many times, a veterinarian will recommend giving a dose of Banamine (Flunixin Meglumine) and continuing to monitor for worsening signs, but usually the signs are self limiting and resolve on their own with time. It is important to treat symptoms quickly so that the horse continues to eat and drink normally. It is recommended to contact your vet at the start of clinical signs before the potential for colic occurs.

Another type of reaction that can occur is a systemic reaction. These reactions are more severe, but are very rare. This type of reaction includes anaphylaxis, vasculitis, or hemolysis. It is important to monitor and communicate any changes in behavior, activity, or appearance after vaccines are administered. Call your vet immediately if you are concerned.

If a vaccine reaction occurs, there are changes a veterinarian can make to decrease the chance of a vaccine reaction happening again in the future. The first is to change the vaccine brand. Horses are often allergic to the additives which vary between different brands of vaccines. The veterinarian may also administer a premedication before vaccines are given to lessen the inflammatory response, or stagger vaccines so multiple are not given at the same time. Regardless, every effort is made to make sure that the horse does not have repeated discomfort and continues to have protective immunity!