What Are the Side Effects of Rabies Vaccinations for Cats

The rabies vaccine is administered by an injection.
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Rabies is a virulent disease with no cure, which is why the vaccination against it is required by law in most areas. While side effects from the vaccine are usually mild, in some cases they are serious. The vaccine is recommended for most kitties because the risk of these side effects is small.

Why Vaccinate?

Rabies is a viral infection that is transmitted through the saliva of an infected animal when he bites your cat. This disease is typically fatal once a cat becomes infected and the disease can also be passed to humans. In humans, the disease is fatal in many cases as well. Because of the risk of infecting people, many states and municipalities have made vaccination against rabies mandatory by law. Because of these laws, your veterinarian is required to give the vaccine to your cat. Even if not required by law in your area, the rabies vaccination is considered a "core" vaccine, which is recommended for both indoor and outdoor cats, according to the Feline Advisory Bureau. It is especially important to vaccinate cats who are allowed outdoors, as the risk of becoming infected is much higher for outdoor kitties.

Mild Side Effects

The vaccination is administered by an injection, usually between the shoulder blades, in one of your cat's hind legs or in the lower back, according to Veterinary Partner. Ask your veterinarian where exactly he has injected your kitty so you can monitor the injection sight. Common side effects include minor swelling at the sight of the injection, less than 1 inch in size, redness, vomiting, sneezing and slight lethargy, according to VetInfo. Symptoms should subside in 24 to 48 hours after the vaccination. Consult with your veterinarian about any symptoms you observe to ensure that something more serious isn't going on.

Serious Side Effects

Some cats are allergic to the rabies vaccine and may have a serious reaction to it, known as anaphylactic shock. Signs of shock include extreme lethargy, reduced appetite, collapse, trouble breathing, vomiting and seizures. These effects usually occur within an hour of the vaccination, according to the Cornell University College of Veterinary Medicine. You must bring your kitty in for emergency veterinary care if you notice these symptoms, as an allergic reaction can sometimes be fatal. In some cases, a protein in the vaccine can cause organ damage. Symptoms of organ damage are similar to those of an allergic reaction, occurring within 45 days of the injection, according to VetInfo. When a live-virus vaccine is used, there is a small chance that your cat could develop rabies itself, according to Pet Informed. Live-virus rabies vaccines should not be used in cats with a compromised immune system because of this reason, nor should they be used in pregnant cats. Expectant moms can suffer the loss of their litter if given a live-virus rabies vaccine.


One of the most serious of the side effects induced by the rabies vaccine is the development of a type of cancerous tumor called a fibrosarcoma. The incidence of this type of tumor ranges from between one in 1,000 and one in 10,000 of cats vaccinated, according to Veterinary Partner. Tumors may take months or years to develop after a rabies vaccination. This type of cancer is very rare, but quite virulent; surgical removal of the tumor is required and your vet may recommend chemotherapy. Once removed, these tumors tend to reoccur quickly and the long-term prognosis is that they are usually fatal.

Cancer Concerns

Some theorize that the aluminum-based adjuvant included in killed-virus vaccines, to stimulate the immune system, could be the culprit behind the development of cancerous tumors, according to the Humane Society of the United States. If you are worried about vaccine-induced fibrosarcoma, have your vet administer an adjuvant-free vaccine and inject the vaccine into your cat's leg. Amputation of the leg in cases of fibrosarcoma prevents the cancer from reoccurring and spreading to other parts of the body.


Cats who suffer from a compromised immune system or those over 10 years old may be exempt from rabies vaccinations required by law in some cases, according to the American Veterinary Medical Association. Certain rabies vaccinations are approved for vaccination in three-year intervals, rather than annual ones. If the laws in your area allow such vaccinations, they may cause fewer side effects because they are administered less frequently. Blood tests, called titer tests, can test your cat's immunity levels. Those with sufficient immunity may be exempt from an annual vaccination, even if required by law, according to the Humane Society of the U.S.

Always check with your veterinarian before changing your pet’s diet, medication, or physical activity routines. This information is not a substitute for a vet’s opinion.

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