Pet Vaccinations: Vaccinations for Your Cat or Dog (cont.)

Is it true that vaccines can even cause cancer?

In cats, definitely, says Richard Ford, DVM, professor of veterinary medicine at North Carolina State University. Ford says most but not all scientists believe the culprit is a chemical called an "adjuvant" that's added to some feline vaccines. "Many [scientists] strongly recommend to avoid using any cat vaccine that is labeled 'killed' or 'inactivated.' All feline vaccines labeled in this way contain adjuvant. Vaccine labeled 'attenuated' or 'recombinant' does not contain adjuvant."

Years ago, vets started noticing tumors forming in the area between the shoulders, where cats are vaccinated. The tumors are rare, occurring in 1 in 1,000 to 1 in 10,000 cats. Veterinarians now give this type of vaccine low on a cats' front or hind legs so they can amputate if a tumor develops, potentially saving the cats' life.

Vaccines can definitely cause cancer, says Luci T. Dimick, DVM, of The Ohio State University. She says feline leukemia is caused by a virus, and it's listed as a "non-core" disease. Yet many vets feel kittens should be immunized even though it's one of the injections, along with rabies, thought to cause cancerous tumors in some cats. Feline leukemia virus is a retrovirus, like HIV in humans, causing white blood cells to grow out of control, which is why it's called leukemia. This overgrowth of white blood cells leads to a type of cancer called lymphoma.

What about other types of reactions?

Vaccines can make pets sick and lethargic and induce diarrhea, Casal says. Fatal reactions, though, are rare. But the controversy over the potential for reactions to the vaccines, she points out, has resulted in a backlash that could have serious consequences. "Sadly," she says, "some pet owners or even vets just trash a lot of vaccines." That means some pets aren't getting the protection they need against disease. "We've seen this in people," Casal says, "which is why we're seeing more mumps and measles." Any treatment carries some risk, she says.

Kate Creevy, DVM, is professor of small animal internal medicine at the University of Georgia. She says it's not known why some animals have reactions to vaccines while others don't. "It may be true that some breeds are more prone to vaccine reactions than other breeds, although this is debatable."

The most common adverse reactions are mild and short-term, including reduced appetite, fever, and swelling at the point of injection. Allergic reactions appear within minutes or hours and may include vomiting, diarrhea, swelling, and difficulty breathing.