Dog Vaccine Side Effects and Adverse Reactions

Dr. Lila Miller, D.V.M, ASPCA

Vaccinations are one of the most important weapons in the fight against infectious diseases in animals. Many diseases have been virtually eliminated through disease control programs that have incorporated vaccination as one of the control measures. However, vaccines are not without their limitations and there are vaccine failures. In fact, in some cases the reactions or side effects can be worse than the disease they are being used to prevent. The use, or overuse of vaccines is being carefully evaluated by veterinary researchers and clinicians the world over. This article will address causes for vaccine failures, side effects and adverse reactions.

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vaccinations side effects

Side Effects and Adverse Reactions


Anaphylactic (or allergic) reactions are amongst the most severe reactions that can be seen after vaccination. Anaphylaxis can occur after any vaccine is administered, but have been most commonly seen with vaccines that have large amounts of foreign proteins, are adjuvanted (Adjuvants are chemicals that are added to enhance the immune response. Killed vaccines commonly are adjuvanted) They may occur after the 2nd or 3rd vaccination in the booster series, or on initial vaccination. It is virtually impossible to predict that an animal is allergic unless a previous reaction has been noted. Vaccines that seem to be most likely to cause reactions include the killed rabies, canine corona, FeLV, and Leptospira vaccine. Although not very common, the clinical signs can range from mild symptoms to life threatening emergencies. The signs may be facial swelling, itching, weakness, diarrhea, difficulty breathing, shock and death. Treatment consists of administration of epinephrine, antihistamines and supportive care.

Animals that have had anaphylactic reactions should be treated beforehand with antihistamines if vaccination is mandatory. To further minimize the risk, avoid using vaccines with multiple antigens, use modified live instead of killed vaccines, make certain the vaccine is not injected into the vein, and use subcutaneous or intranasal vaccines instead of intramuscular ones if possible.

Autoimmune hemolytic anemia

Autoimmune hemolytic anemia (AIHA) has been reported in dogs vaccinated with modified live multiple antigen vaccines, particularly parvo. There can be many causes of AIHA, but vaccination seems to trigger antibody production against red blood cells, resulting in a variety of signs including weakness, lethargy, loss of appetite, exercise intolerance, difficult breathing, increased heart rate, vomiting, diarrhea. It can be life threatening and require lifelong therapy, including fluids, steroids, blood transfusions, etc.

Local reactions

Local reactions include pain, swelling, abscesses, redness and irritation. Granulomas, or hard tissue formations may occur at the site of vaccination. These symptoms can occur within minutes to 1 week after vaccination but usually resolve on their own. Animals with local reactions should be treated symptomatically, observed carefully and reported to the veterinarian if they persist.

Systemic reactions

Systemic reactions include fever, depression, loss of appetite, lethargy and weakness. They usually appear within 1-2 days of vaccination and then disappear.

Nervous system problems

Nervous system problems have been seen after vaccination with modified live rabies (no longer available) and canine distemper vaccines. It appears that these vaccines actually caused disease symptoms.

Reproductive system problems

Prenatal infections, fetal malformations, infertility and abortion can result from the use of modified live vaccines in pregnant animals. This is most commonly seen with the use of the panleuopenia (distemper) vaccine in cats. Kittens are borne with a problem called cerebellar hypoplasia, which results in an inability to maintain balance.

Musculoskeletal problems

Kittens vaccinated against calici virus may develop a fever and limping approximately 1 week after vaccination. Treatment with painkillers, fluids and antibiotics is usually effective.

Post vaccination sarcomas

The debate about the safety of vaccines took the forefront in small animal medicine when a possible link was discovered between vaccination and the development of a form of cancer known as sarcomas. Sarcomas are aggressive, locally invasive tumors that seem to form at the site of vaccination in cats. They occur most often with the use of killed, adjuvant vaccines- notably rabies and FeLV. The most common cancer is fibrosarcoma. It usually appears from 3 months to 4 years after vaccination. The prevalence of this problem has not been established, but it may be anywhere between 1:1,000 or 1:10,000 vaccinated cats. A veterinary task force has been formed to research the issue. Treatment is most successful when the tumors are discovered early and surgically removed with a very wide incision. Recurrence is common if the incision is not wide enough to remove all tumor cells. This problem was the catalyst for the American Association of Feline Practitioners to revise its recommendations regarding the frequency and anatomic sites of vaccination, as well as exposure risk assessment of individual animals.

Respiratory disease

The clinical signs of respiratory disease may be seen in animals vaccinated with intranasal vaccines against herpes and calici viruses and bordetella. Cats will sneeze and have runny eyes, but usually continue to eat and act normal otherwise.

Virus shedding

Virus shedding can occur with the use of modified live vaccines. The virus that is shed does not normally cause disease, but there have been reports of this occurring.

Interference with disease testing

The results of some disease tests must be interpreted carefully if animals have been recently vaccinated.


Maternal antibody interference

Very young animals receive antibodies from their mothers when they nurse that protect them from disease. While these antibodies are present, vaccination will not be effective. These antibodies generally disappear from the body at 12-14 weeks of age. Booster shots are timed to try and protect them when the maternal antibodies wane at that time.

Certain drug therapies

For example, high doses of steroids are immunosuppressive and may interfere with vaccinations. The use of antibiotics may also interfere with vaccination.

Fever or hypothermia

Already debilitated, exposed or incubating disease


Vaccine being used is against wrong strain of disease agent

Vaccine inappropriately administered

Improper storage of vaccine
Improper route of administration
Disinfection of skin or needles
Improper vaccination intervals (too often or too long)


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