Question: Dr. Utchen, is it true that vaccinations can cause tumors? My cats live indoor only, should I still vaccinate them annually?
For years routine immunization of cats, dogs, and people has been the basis of preventive health care. However, depending on a particular animal's risk of contracting certain infections, not all immunizations are necessary or wise.
There are several diseases for which a cat can be at risk.
Cats that venture outdoors are at risk for contracting any infectious feline disease. This includes two feline upper respiratory infections (Feline Viral Rhinotracheitis and Calicivirus), Panleukopenia (otherwise known as "Distemper"), Feline Leukemia, and Rabies. Effective immunizations exist for all of these diseases. With the exception of Feline Viral Rhinotracheitis, these diseases are potentially fatal infections for which no effective medical cure exists.
Rabies is a zoonotic disease, meaning it can be transmitted from other animals to humans. While the Feline Leukemia Virus is not zoonotic, it is fatal during the first 3 years for over 50% of the cats that contract it. Cats that live strictly indoors by themselves or who live with other cats that are strictly indoors, are not at risk for contracting Feline Leukemia or Rabies. These two infections are spread only by being bitten by other animals.
Other common infectious diseases that exist for cats, but for which there is no effective immunization, are the Feline Immunodeficiency Virus (analogous to HIV) and the Feline Infectious Peritonitis Virus.
The tumors you have heard about are called Vaccine Associated Sarcomas. These are a class of tumor that develops underneath the skin or inside the body. Various studies have implicated the immunizations against the Feline Leukemia Virus and Rabies as causing sarcomas at the site of immunization in a very small percentage of cats. The estimates range from as low as 1 in 25,000 cats up to 1 in 1,000 cats. These tumors first appear as a small bump under the skin where the immunization was given, and can occur any time from a few weeks to over two years after immunization. If detected early they can be removed. If they are advanced before surgery is attempted, there is a high likelihood of regrowth after surgical removal.
Generally, for indoor cats, I no longer recommend immunization against the Feline Leukemia Virus or Rabies.
For cats that go outdoors, we now immunize with an non-adjuvanted Rabies vaccine formulated to reduce the risk of developing vaccine-associated sarcomas. An adjuvant is an additive that increases the body's immune response to an immunization. Adjuvanted vaccines induce immunity which lasts longer, but can be irritating to the tissues under the skin. This irritation is believed to contribute to the development of vaccine-associated sarcomas.
Immunizations are now given in different locations to further reduce the amount of subcutaneous irritation at any one location as a result of immunization.
In contrast to cats, this does not occur in dogs.
As always, my concern is the overall health and well-being of your cat. Please feel free to discuss this information with your veterinarian if you have any questions.