Vaccine Response OR Reaction

Vaccines help our pets to stay healthy. They prevent many diseases from infecting our animals and they reduce the severity of other diseases. The benefits of having your pet vaccinated far outway the risks.

Vaccine response and vaccine reaction are two terms that are often misunderstood when it comes to immunizations. In this article, we will discuss what is a normal response to a vaccine and what is a reaction that is concerning.

Vaccine Response

It is normal for animals to have a physical response after receiving a vaccine. Some vaccines can make you feel quite pukey (remember your COVID vaccine? ) This is a NORMAL response to the vaccine and it means that it’s working.

When your pet receives a vaccine their bodies immune system recognizes the “threat” and starts to build a response. This response is exactly what we want to happen. It means your pet is developing immunity and will fight any future occurrences with that virus.

During this time when your pet is developing that response, they may experience some symptoms. Lethargy is a common response of the body. When the body rests the cells and immune system can be hard at work.

Common Responses:

  • Tired
  • Soreness or a lump around the injection site
  • Generally “off” and not their normal self
  • Sneezing – some vaccines such as Bordetella bronchiseptica and parainfluenza virus are delivered in the nose and may cause some sniffles.

These symptoms usually only last for two or three days. If they persist call your vet’s office and let them know.


Severe reactions to vaccines are rare. One study followed 1,226,159 dogs and only 4,678 (less than 1%) had adverse reactions which included hives, discharge at the injection site, allergic reaction, and anaphylaxis. 

In rare cases, your pet may have a severe reaction. If you feel your pet is having a severe reaction call your vet’s office right away.


This is a severe allergic reaction that may result in itchiness, facial swelling, vomiting, diarrhea, and/or respiratory distress. This typically happens soon after the injection.

Your vet will have medicine on hand to counter anaphylaxis.


Rarely an animal develops a severe reaction at the sight of the injection. Symptoms include very red skin, discomfort, discharge, and swelling. This would be more severe than the normal response to having some irritation and continue to increase over several days.

Call your vet if this is occurring.

Auto-Immune Disease

This has been a popular argument among anti-vaxxers. Pets very rarely develop an auto-immune disease due to vaccination. There are a number of things that can cause a pet to develop an auto-immune disease such as genetics and environment. The research is ongoing.

If your pet has auto-immune diagnoses discuss with your vet the best way to handle vaccinations.

Titer Tests

If you are concerned about your cat or dog having too many vaccines or you are unsure which ones they have had your vet can do a titer test.

Sometimes if you adopt a stray animal you don’t know their medical history. Remember, it’s important to keep good medical records!

A titer test is a blood sample that allows your vet to measure the antibodies in the animal’s body. Their bodies form antibodies when they have had the vaccine or the actual disease.

Reasons To Vaccinate Your Pet

  1. Vaccinations prevent many pet illnesses
  2. Vaccinations save you money. Treating a disease can be very expensive.
  3. Vaccinations prevent zoonotic diseases that pass between humans and animals
  4. In Northern Kentucky, distemper is prevalent in several wildlife species and can pass to your pets.
  5. When it comes to rabies, vaccination is the law. Unfortunately, we do see rabies in unvaccinated pets every year.

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