Allergic Reaction to Vaccines in Cats

A vaccine is the modified form of an organism, containing the antigens for a disease that is not infectious. When the agent is injected, the immune system responds by creating antibodies for that specific infectious organism. The purpose of the vaccine is to stimulate the immune response to make specific cells to keep circulating the body. Therefore, when the feline is exposed to the virus or bacteria again in 'real life', the immune system is prepared to fight it. 

Rarely, the immune system overreacts, causing an allergic reaction to vaccines in the feline. Symptoms of an allergic reaction can be mild, moderate or severe, and vary depending on the type of vaccination received. 

Your cat’s immune system plays a vital role in protecting the body from infectious ailments to keep her healthy. Making antibodies against parasites, microbes, bacteria and viruses is one of the most important functions of the immune system. Unfortunately, this complex system cannot make specialized cells to fight every disease that invades the body, so vaccines are given to help the immune system prepare. 

It is normal for a cat to experience a few mild side effects after receiving her vaccines, such as local swelling or pain at the injection site. This is not an allergic reaction.

Your cat could be having an allergic reaction to a vaccine if they develop more worrying signs such as hives, facial swelling, difficult breathing or collapse.

An allergic reaction to vaccines in cats can be mild, moderate or severe and can appear within a few hours  after the vaccination was given. Severe reactions are usually associated with killed varieties of vaccines such as feline leukemia virus and rabies. 

Mild Vaccine Reaction

• Fever
• Loss of appetite 
• Swelling, redness or pain at the injection site
• Temporary lameness 
• Temporary joint soreness 
• Sneezing lasting roughly 4-7 days
• Low activity levels 

Moderate Vaccine Reaction 

• Urticaria (hives) 
• Pruritus (itchy skin)
• Swelling of the neck, eyes and/or lips
• Redness 
• Fever

Severe Vaccine Reaction: 

• Breathing difficulties 
• Diarrhea
• Vomiting 
• Decreased blood pressure 
• Pale mucous membranes
• Cold extremities 
• Cardiac arrest 
• Shock 
• Seizures
• Collapse 
• Death 

An allergic reaction to vaccines in cats is caused by an over-reactive response to the immune system. The antigen within the vaccine is used to stimulate the cat’s immune system to create specialized antibodies against the virus, bacteria or disease. However, the nature of some feline immune systems are hypersensitive and overreact to the introduced antigen. Common feline vaccinations that have been known to cause an allergic reaction in cats include vaccines against: 

• Feline Panleukopenia
• Giardiasis
• Bordetellosis
• Feline Immunodeficiency Virus
• Feline Infectious Peritonitis
• Chlamydiosis
• Feline Leukemia Virus
• Rabies
• Feline Herpesvirus and Feline Calicivirus

Allergic reactions can be caused by a variety of elements in your cat’s environment e.g. a wasp sting, causing similar symptoms of a vaccine allergic reaction. Therefore, the veterinarian may want to perform a differential diagnostic exam such as an intradermal allergy test to rule out other causes. 

To diagnose an allergic response to vaccines specifically, the veterinarian will review your feline’s current vaccination history, paying close attention to which vaccines were scheduled to be administered. The vaccination history will reveal which vaccines were administered, the date of administration, and location. The doctor can then pair the medical record with your cat’s current condition to diagnose the allergic reaction to a vaccine. 

Mild to moderate cases of an allergic reaction can be symptomatically treated with anti-inflammatory drugs such as a corticosteroid and anti-histamines. A feline with a mild or moderate allergic reaction to vaccines should return to normal health within a week. However, moderate allergic reactions can worsen over time and become severe, so the feline will need to be monitored for the duration of the allergic response. 

Cats with a severe allergic reaction to vaccines need to be rushed to the veterinary emergency clinic right away. The doctor will begin administering life support to the feline including intravenous fluids and oxygen. The feline’s airways will be monitored to ensure they do not close at any time. Felines that are stabilized will likely survive anaphylaxis, but will require hospitalization for a couple days after anaphylaxis shock before returning home.

Allergic reaction to vaccines in cats is very rare, but if your feline has a history of vaccine hypersensitivity talk to your veterinarian. The next time the vaccine is needed, the veterinarian may include an antihistamine to prevent an adverse reaction or eliminate the vaccine from your cat’s vaccination schedule altogether. The vet may also decide against giving the vaccine, depending on the specific circumstances.

 It is important to discuss vaccinations with your veterinarian to fully understand the risks and benefits that come from vaccines. In most cases, the benefits of vaccinating your cat far outweigh the risks, which are small by comparison. 

Paying to treat an allergic reaction out of pocket can be a major financial burden. Fortunately, most pet insurance companies reimburse claims within 3 days, putting 90% of the bill back in your pocket. In the market for pet insurance? Compare leading pet insurance companies to find the right plan for your pet.