Rabies Vaccine Allergies in Cats

Some cats may develop a more serious reaction than others. If this happens, the vet can alter the cat’s vaccination schedule, which may help to reduce the possibility that it will develop an allergic reaction. Using a vaccine made from an inactivated virus may also help.Sensitivity to the rabies vaccine is also possible when a killed virus has been used in the vaccine. This happens because the vaccine has a higher amount of viral or bacterial particles per dose, along with additional chemicals which are intended to boost the cat’s immune response. Allergic reactions are potentially serious and should be considered to be veterinary emergencies.

Rabies vaccine allergies are mostly mild reactions to the ingredients in the rabies vaccine. It is mandatory in several states and municipalities that all cats and dogs receive this vaccine to prevent them from developing a deadly disease that can be spread to humans. 

Allergic reactions to a rabies vaccine vary from mild to serious or deadly:

Mild allergic reactions (If these persist for more than a day, call the vet):

• Decreased activity
• Reluctance to eat
• Mild cough (after intranasal vaccine)
• Sneezing (after intranasal vaccine)
• Visible nasal discharge (“snotty nose”)
• Vomiting

Serious or severe allergic reactions are potentially fatal and are considered a veterinary emergency. If your cat develops these symptoms, get to the vet right away:

• Anaphylactic shock 
• Facial swelling
• Hives
• Itchy skin
• Diarrhea
• Cold paws
• Pale gums
• Severe coughing 
• Difficulty breathing
• Vomiting
• Seizures
• Rapid heart rate
• Weak pulse
• Coma

Causes of rabies vaccine allergies include:

• Live-virus vaccines
• Adjuvants (chemical compounds added to vaccines to make them more effective)
• Breed predisposition (the risk of allergies to vaccine is higher in a purebred cat)
• Adding leptospirosis vaccine to rabies vaccine
• Giving multiple vaccinations at one time
• Developing sensitization to vaccine ingredients—the cat’s body “remembers” the vaccine and its ingredients, setting the cat up for a future allergic reaction

When a vet sees a cat experiencing a true allergy to a rabies vaccine, they need to act quickly, especially if the cat’s symptoms are serious or severe. They thoroughly examine the cat, making note of itchy skin (urticaria), hives, whether the muzzle is swollen, and if the cat is having trouble breathing. The vet will hear the cat’s heart beating rapidly. When they feel for the cat’s pulse, it will be weak and possibly thready.

If the cat has persistent diarrhea or vomiting, the vet is able to make a stronger diagnosis of anaphylactic shock syndrome. This condition is potentially deadly, meaning the vet needs to begin treatment immediately. If the anaphylactic reaction isn’t stopped and reversed quickly, the cat’s blood vessels begin leaking fluid into the cat’s organs. 

If the cat develops anaphylactic shock, the vet will immediately ensure that its airway is open and that the cat can breathe. The cat will be given supplemental oxygen and intravenous fluid. Finally, the cat will be given epinephrine and antihistamines to reverse the anaphylactic reaction. Rapid-acting corticosteroid injections may also be given to reduce any inflammation the cat may develop.

Once the vet knows a cat is allergic to the rabies vaccine, they will give the cat prophylactic antihistamines before giving the rabies vaccine to the cat in the future. Because this vaccine is required by law in so many cities and states, it can’t be avoided. 

The vet may also insert a catheter into one of the cat’s veins so that, in the event of a severe anaphylactic reaction, medication can be given right away. Because the cat has an allergy to the rabies vaccine, or any of its ingredients, they may want the cat to stay in their office for at least thirty minutes after receiving the shot. This stay may extend to several hours so the vet can watch for a delayed reaction. This isn’t a surefire protection against a life-threatening reaction. These can develop several hours after the cat is vaccinated with a rabies vaccine.

If the cat develops a mild allergic reaction, it will recover, although the vet and pet owner should keep a close eye on it to ensure it doesn’t develop a severe allergic reaction (anaphylaxis).

For the cat that develops true anaphylaxis, it may recover if it is taken to the vet and seen immediately. Once medications and supportive care are given to the cat, its reaction will reverse under veterinary supervision.

Once the cat has displayed mild or severe allergic reactions to the rabies vaccine, the vet should ensure that the cat can safely receive future vaccinations. Reducing the frequency of this vaccine may help. Choosing vaccines without adjuvants and giving only one vaccination per visit may also help. Avoiding the brand of rabies vaccine that caused the allergic reaction is vital in avoiding future reactions. The vet or their assistant can also inject the vaccine subcutaneously or give the cat an intranasal vaccine instead of giving the cat an intramuscular injection. Finally, vaccine with a killed virus instead of a live virus should be given.