Feline Vaccination Side Effects

Feline vaccinations are administered to cats in order to protect them from severe viral infections and contagious diseases. Vaccines are categorized as core or noncore vaccines. Core vaccines are those that have to be administered to all pets. Noncore vaccines are administered to cats that are at risk of contracting certain diseases.

Core Vaccines Recommended for Cats Include:

  • Panleukopenia
  • Rhinotracheitis
  • Calcivirus
  • Rabies

Administration of Vaccines

Vaccines are administered as early as 6 weeks of age. Some vaccines require booster shots for a period of three years. Vaccines are also available as injections or intranasal drops. The two types of commonly used vaccines are modified live vaccines and killed vaccines. Modified live vaccines are most suited to pets with strong immune systems. Cats with suppressed immune systems may develop vaccine related diseases if injected with modified live vaccines. Killed vaccines are safer for use but increase the cat's susceptibility to vaccine associated sarcomas. Although the effect of the vaccine differs in individual pets, newer vaccines are safer for use and the risk associated with vaccines is far less in comparison to the risk of developing the disease.

Reactions to Vaccinations

The side effects of vaccination vary according to the pet's age, breed and the type of vaccine administered. Although some side effects are temporary and subside within several hours, other side effects that are prolonged or more severe require medical attention. Amidst various side effects caused by vaccines, pets most commonly suffer from neurological symptoms and swelling at the injection site.

Common Side Effects of Vaccines Include:

  • Allergic reactions
  • Drowsiness
  • Pain at the injection site
  • Lump at the injection site
  • Lameness
  • Fibrosarcoma 
  • Anaphylaxis


This is a life threatening side effect that isn't common in cats. However, the symptoms of anaphylaxis are seen in conjunction with the feline leukemia vaccine and rabies vaccine. Anaphylaxis occurs when the cat's body has an allergic reaction to the ingredients present in the vaccine. Pets suffering from anaphylaxis develop a swelling of the facial muscles and cardiac abnormalities. In order to prevent death in cats suffering from anaphylaxis, the vet will use epinephrine and IV fluids to stabilize the pet.

Vaccine Associated Sarcoma

Vaccine associated sarcoma develops in pets administered the FeLV vaccine. The sarcoma may start as a small lump at the injection site which develops into a tumor. Lumps that persist for a long time or develop into tumors require prompt medical help. Tumors that are malignant are usually very invasive and the cat will require chemotherapy or combination therapy to slow disease progression. Research has established that pets develop sarcomas due to the adjuvants present in killed vaccines. Studies also suggest that genetic predisposition increases the risk of developing sarcomas. Pet owners should monitor any lumps that persist even one month after vaccination.


Pet owners should discuss with the vet, vaccines suited to individual cats. If diseased cats are living in the same neighborhood, additional or frequent booster shots may be necessary. Most side effects disappear within a few days. However, pets that develop unusual symptoms or refuse to eat or drink water should be taken for a vet check.

Although vaccines are an effective way to protect pets from certain viruses, they may not provide complete protection. It's important to follow other precautionary measures to ensure optimal health in cats.