What To Know About Possible Vaccine Reactions in Dogs

Dr. Shawna Abrams
By Dr. Shawna Abrams on Jul. 19, 2023

In This Article


What Is a Vaccine Reaction in a Dog?

The American Animal Hospital Association (AAHA) recommends that all dogs, regardless of lifestyle, be vaccinated with core vaccines unless there’s a medical reason not to vaccinate.

A vaccine is an injection of a killed or altered microorganism that works by stimulating the body’s immune system to react to an imitation infection. This response helps the body learn how to fight the infection should it be exposed to it in the future. However, when the immune system is stimulated in this way, there can be possible side effects. These side effects are called a vaccine reaction.

Symptoms of a Vaccine Reaction in Dogs

When the immune system is stimulated by a vaccine, mild side effects are common. However, if these side effects last longer than a day, you’ll want to contact your veterinarian.

Mild side effects from a vaccine include:

  • Tenderness or pain at the site of injection
  • A low-grade fever
  • Fatigue
  • Reluctance to eat or eating less than normal
  • Coughing or sneezing if your pet received an intranasal (through the nose) vaccine
  • A small bump at the site of injection
    • If this bump develops, it may take up to two weeks to resolve. If you notice any redness, swelling, pain, or discharge worsening one to two days after vaccination, it’s important to call your veterinarian.

More severe side effects from a vaccine, though rare, can occur—including serious immune-mediated reactions. This is where the dog’s immune system attacks the body’s own cells.

Type I hypersensitivity, or anaphylaxis, is potentially life-threatening and requires immediate veterinary attention.  Clinical signs of an anaphylactic, life-threatening reaction are:

  • Severe coughing

  • Vomiting or diarrhea

  • Hives

  • Swelling on the face, nose/muzzle, or around the eyes

  • Difficulty breathing

  • Collapse

If you see any of these signs after vaccination, it’s important to contact your vet or an emergency clinic because it could indicate a serious issue.

Most Common Vaccine Reactions in Dogs

A 2005 study of more than 1 million dogs found that there was a reaction rate of about 1 in 260 dogs, and included any type of reaction regardless of severity. The study found that young dogs, small-dog breeds, and Boxers were at a higher risk for adverse reactions. The top five at-risk breeds were Dachshunds, Pugs, Boston Terriers, Miniature Pinschers, and Chihuahuas

Although reactions are possible any time the immune system is stimulated by a vaccine, the following are the most common core and non-core vaccines for dogs and their associated reactions:

Canine Distemper Vaccine

Canine distemper virus is a contagious and potentially life-threatening virus. The vaccination for canine distemper virus (CDV) is considered a core vaccine, meaning that it’s recommended for all dogs regardless of location.

Possible side effects include both mild and severe side effects.

Mild side effects may include:

  • Tenderness or pain at the site of injection

  • A low-grade fever

  • Fatigue

  • Reluctance to eat or eating less than normal

  • A small bump at the injection site

Severe, potentially life-threatening side effects may include:   

  • Severe coughing

  • Vomiting or diarrhea

  • Hives

  • Swelling on the face, nose/muzzle, or around the eyes

  • Difficulty breathing

  • Collapse

Canine Parvovirus Vaccine

Canine parvovirus is another highly contagious virus that can cause nasal disease in dogs. Although serious, the disease is preventable with vaccination. It’s also considered a core vaccine.

Although there are no specific reactions to the parvovirus vaccine itself, mild side effects as well as rare but serious side effects, such as those listed above, can occur.

Rabies Vaccine

Rabies is a viral infection that can affect any mammal, and once symptoms are seen, it’s fatal. Because rabies can be transmitted to humans and is a fatal disease, it’s a core vaccine and highly recommended for all dogs/pets and horses.

The rabies vaccine is a killed vaccine and side effects may include fever, loss of appetite, and soreness at the injection site. 

Kennel Cough Vaccine

Bordetella bronchiseptica (Bb) is one component in the disease kennel cough, which also includes canine parainfluenza virus (CPIV), canine adenovirus 2, canine influenza virus, and sometimes canine distemper virus.  

Possible side effects include mild symptoms of kennel cough: sneezing, running nose, slight cough, reduced activity, reduced appetite, and a low-grade fever.

Leptospirosis Vaccine

Canine leptospirosis is a common bacterial infection that can be caused by many different strains of Leptospira bacteria, and all mammals are potentially at risk. This is considered a non-core vaccine, but because it can be spread between animals and humans and is potentially life-threatening, vaccination is recommended.

Like the rabies vaccine, the leptospirosis vaccine is a killed vaccine and there’s often concern about including it in the distemper-combination vaccine. The concern stems around the large number of proteins in the vaccine; both the killed organism and an added ingredient to enhance the immune response (called an adjuvant), contain proteins. However, the vaccine has been reformulated to minimize reactions. Now, it’s thought that there are less than 53 adverse reactions for every 10,000 doses given.

To help reduce the chance of a vaccine reaction, it’s recommended that dogs receive their initial vaccine at 12 weeks or older. Until 12 weeks, some vets will recommend receiving the distemper-combination vaccine that does not include leptospirosis. Then, beginning with the 12-week booster, the first distemper combo that includes leptospirosis can be given. Two doses are required regardless of your pet’s age.

Lyme Vaccine

Lyme disease is caused by a bacterial infection, Borrelia burgdorferi, which is transmitted by tick bites, primarily by the black-legged tick (aka deer tick) and the Western black-legged tick. The Lyme vaccination is a non-core vaccine and is best discussed with your veterinarian, based on lifestyle and location.

Although there are no specific reactions to the Lyme vaccine itself, like the others, common side effects and rare but serious side effects can occur.

As with all vaccines, serious, life-threatening reactions can occur and it’s very important to seek veterinary care if you see any serious side effects.

Vaccination Failure

When a vaccine fails to provide protection in a young dog, the most common cause is the presence of antibodies that a mother dog passes to her puppies; these antibodies interfere with the immune response of the vaccination. For this reason, vaccination typically starts around 8 weeks of age, with boosters occurring every three to four weeks to ensure maternal antibodies have waned and there’s a strong immune response.

In older dogs, immunosenescence is the most common reason for vaccination failure. Immunosenescence is an age-related decline of the immune system; the immune system doesn’t produce a protective-level response to the vaccine. Because of this, dogs are at a higher risk for developing an infectious disease from the vaccine and becoming sick from it.

Treatment of Vaccine Side Effects in Dogs

Treatment for side effects largely depends on the severity and extent of the side effects. Usually, treatment is only recommended in severe cases. However, your vet may prescribe a medication to help your pet feel better.

In severe, life-threatening reactions, treatment typically consists of medications such as antihistamines, steroids, IV fluids, and oxygen. In extremely serious cases, dogs need to be intubated and put on a ventilator to help them breathe.

If you notice any vomiting, diarrhea, swelling, areas of redness, trouble breathing, or collapse following a vaccination, contact your veterinarian or an emergency clinic immediately.

Keeping Dogs Safe During and After Vaccines

If your dog has had any type of reaction to a vaccine, it’s important to let your veterinarian know what the reaction was, no matter how mild. Reactions can become more severe with subsequent vaccinations.

Additionally, some dogs are more likely to have a vaccine reaction because of their genetics, including small-breed dogs and Boxers. In those cases, or for dogs that have had a previous reaction, consider talking with your vet about medicating your dog before the vaccination. Sometimes medications like antihistamines can be helpful in controlling an immune-mediated reaction.

Risk for an adverse reaction is increased when more than one vaccine is given at one time; however, this is not true for combination vaccines. For example, the distemper/parvo combination is considered a multivalent vaccine, meaning multiple organisms are mixed in one vaccine. No increase in risk has been found with a multivalent vaccine.

However, giving multiple vaccines at one time (for example, a single rabies vaccine plus a distemper/parvo combination vaccine) or within two weeks of each other can potentially interfere with the immune response and increases the risk for an adverse reaction. Separating vaccines by at least two weeks can help reduce risk of a reaction, and allows for a more controlled study as to which vaccine caused an adverse event.

Overall, vaccines for dogs are safe, and the lifesaving benefit and protection outweigh the potential for a serious adverse reaction.

Vaccine Reactions in Dogs FAQs

Do dogs typically feel unwell after a vaccine?

Yes, it’s very common for dogs to have less energy, a mild fever, and to not want to eat.

How long after a vaccine would a dog have a reaction?

Serious allergic reactions can occur as soon as minutes or as long as hours after the vaccination. If you’re concerned about the risk of a serious reaction, talk to your veterinarian before they give the vaccine. You can also ask to have your dog stay in the clinic for one to two hours for observation after the vaccine is given. Most reactions occur within the first 24 hours after vaccination.

Will a half or lesser dose of a vaccine prevent a reaction?

A smaller dose does not prevent or reduce the risk of a reaction; in fact, giving a lesser dose may contribute to vaccination failure and not provide protection. In some jurisdictions, it may be illegal to give a lesser dose for a rabies vaccine.

Featured Image: iStock.com/macniak


Dr. Shawna Abrams


Dr. Shawna Abrams


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