Are Leukemia Shots for Cats Necessary if They Test Negative?

Make the decision in my best interest, please.
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Feline leukemia is a scary and deadly disease. Count it a blessing when you find out your cat tests negative for it. What's the next step? Vaccination protects your cat, but there's a slight risk of another type of cancer. Your vet can advise you on what's best for kitty.

Feline Leukemia

The feline leukemia virus doesn't actually cause cancer in a cat; it got its name because its symptoms mimicked those of leukemia. The virus breaks down a cat's immune system, making him vulnerable to all kinds of secondary infections. These include issues with his blood. If a cat tests positive for the feline leukemia virus, meaning he has the virus, there is no point in giving him the vaccinations. A cat with feline leukemia doesn't have a good prognosis, although how long he lives depends on factors such as supportive care.

Spreading the Virus

Cats catch the feline leukemia virus from other cats. An infected mom can pass it to her kittens, or cats spread it through scratches and bites. Sometimes it takes only slight contact with an infected cat for another feline to catch the virus, so you need to keep infected cats quarantined.

If your cat goes outside at all, it's a good idea to have him vaccinated. The American Veterinary Medical Association recommends feline leukemia vaccines "for all cats at risk of exposure to the virus." If your cat stays indoors all the time with little or no chance of contact with other cats, that's another story.


If a cat tests negative for the feline leukemia virus, you have the option of vaccinating him against the disease. The vaccination does not provide 100 percent immunity against the virus, so you must still take precautions. The vaccine consists of a weak version of the virus that doesn't harm the cat, but the cat's body produces antibodies against the vaccine version that should work to protect him if he's exposed to the true virus. Your vet injects the initial vaccine in two doses with a three-week interval. After that, your cat receives an annual booster shot.

Sarcoma Risk

You might be thinking, What's the harm in vaccinating? Isn't it better to be safe than sorry? Well, yes, except that some cats develop sarcomas at the injection site. These malignant tumors are believed to be vaccine-related. According to the University of California Davis School of Veterinary Medicine, the transdermal version of the vaccine doesn't produce chronic inflammatory reactions. These reactions occur at the injection site prior to any sarcoma. However, the efficacy of this vaccine is not as certain as the standard version.

What to Do?

Sit down with your vet and weigh the pros and cons of vaccinating your cat against feline leukemia. Of course, vaccination's essential unless your cat is at very low risk. Could he escape from the house and encounter an infected cat? Is there any risk that he could inadvertently come into contact with a FeLV-positive cat, say if you went away on vacation and left him with a friend who has cats? If the chance is very low, see how your vet feels about forgoing the vaccination. Remember, if your living situation changes, raising the chance of exposure to the virus, you can always go ahead and vaccinate.

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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