Vaccine Reactions

What Is a hypersensitivity or allergic reaction?

Just like humans, dogs and cats have immune systems designed to protect them against a variety of diseases or infections caused by bacteria, viruses, and fungi. When the body encounters a harmless substance, called an allergen, the immune system fights it off by creating specific antibodies. In some animals, this process can lead to a severe, potentially life-threatening allergic reaction known as anaphylaxis. This type 1 hypersensitivity reaction will then trigger cells to release chemicals causing the symptoms discussed below.

Clinical signs due to a vaccine-induced “allergic reaction” appear quickly, often within minutes or hours. Usually, the more rapid the signs appear, the more severe they tend to be. Anaphylaxis can involve one or more body systems such as the skin, respiratory system, cardiovascular system, gastrointestinal tract, liver and/or the nervous system.

Common clinical signs

A hot topic with many pet owners is whether to vaccinate your pet due to the fear of them having a reaction. You may have heard from your next-door neighbor that his dog recently had a severe allergic reaction to her vaccine and had to go to the emergency veterinary hospital. You might be thinking, “What if that happened to my rambunctious puppy?”. It is true that some dogs and cats can develop a reaction to vaccines, but not all signs are considered severe. Below we will look at the difference between normal and uncommon clinical signs.

Common, Mild Signs 

At The Injection Site You May See:

  • Pain
  • Swelling
  • Redness
  • Inflammation

Other Clinical Signs:

  • Mild Fever
  • Lethargy
  • Itchiness

Less Common Signs Needing Veterinary Care 

  • Rash
  • Hives
  • Vomiting
  • Diarrhea
  • Wheezing
  • Trouble breathing
  • Blue/purple gum color
  • Increased respiratory rate
  • Irritated or inflamed eyes
  • Irregular heartbeat or rate
  • Low blood pressure
  • Cardiac arrest
  • Weakness
  • Collapse
  • Seizures
  • Painful abdomen
  • Increased salivation


What The Veterinary Clinic May Do

Depending on the severity of the reaction, your veterinarian might give your pet corticsteroids, antihistamines, or a medication that can help them breathe easier. In severe cases, epinephrine or atropine may be needed if cardiovascular collapse develops. If needed, the veterinarian can provide supplemental oxygen, IV fluids, and may recommend hospitalization.


How To Prevent Vaccine Reactions in The Future

If you know your dog or cat has a history of hypersensitivity reactions to certain vaccines, please let your veterinarian and their staff know so they can discuss options for what is best for your pet.



Written by:

Jessica Hall, DVM student extern, Midwestern University Class of 2022

Shannon Boos, CVT, Veterinary Information Specialist