Feline Leukemia Virus Vaccination

By Rania Gollakner, BS DVM; Ernest Ward, DVM

What is feline leukemia virus?

Feline leukemia virus (FeLV) is a virus that infects only cats. It depresses the immune system and cats tend to remain infected for life. FeLV is an important cause of anemia in cats and can cause several types of cancers. It is found worldwide and is transmitted through the exchange of bodily fluids (such as from a bite), but it can also be transmitted from mother to kitten.

There is no treatment to eliminate the FeLV virus from the body and the disease is ultimately fatal. Therefore, preventing FeLV infection through vaccination is highly recommended. For further details on this important disease, see the handout "Feline Leukemia Virus Disease Complex".

Is there a test for FeLV infection?

Special blood tests have been developed to detect the presence of the virus in a cat's blood. In general, these tests are very reliable, although rarely, a false positive result can occur. In some situations, it may be necessary to confirm infection by repeating blood testing or through different types of testing.

Does my cat need to have a blood test before vaccination?

For the majority of cats, a blood test is highly recommended prior to vaccination to determine whether a cat has been infected with the FeLV virus. If your cat tests positive for FeLV, there is no benefit in administering the vaccine, as it will not offer any protection against the virus.

How safe is the vaccine?

FeLV vaccines have been specially developed so they do not cause the disease. You are unlikely to see any adverse effects apart from some mild sluggish behavior a day or two after the vaccine is given. A very few cats may have a mild allergic reaction. Most vaccine reactions occur almost immediately and your veterinarian will provide appropriate treatment. If you are concerned that your cat is experiencing an abnormal reaction in the hours or days following any vaccination, contact your veterinarian.

A rare form of soft tissue sarcoma known as vaccine-associated or injection-site fibrosarcoma has been associated with a reaction to components in some vaccines. This association is controversial and a considerable amount of research is underway to determine what role vaccines may play in the development of sarcomas. The benefits of vaccination greatly outweigh these small risks in most situations, particularly for cats at risk of exposure (for further information, see the handout "Post-vaccination Sarcoma In Cats").

"The benefits of vaccination greatly outweigh these small risks in most situations, particularly for cats at risk of exposure."

How effective is FeLV vaccination?

FeLV vaccines have been available for many years and have been continuously improved upon. They are helpful in preventing infection with FeLV and, therefore, in controlling FeLV-related disease. Unfortunately, no vaccine is 100% protective. When possible, do not allow your cat or kitten to come into close contact with known FeLV-infected cats or cats of unknown vaccination history.

Based on recommendations by the American Association of Feline Practitioners, current research and expert opinion recommend FeLV vaccination for all kittens, and then on an as-needed basis for adult cats. Although the FeLV vaccine is not considered a core vaccine in adult indoor cats, it is highly recommended for cats that spend time outdoors. Your veterinarian can discuss the pros and cons of vaccinating your cat against this disease based on her specific lifestyle and risk of exposure.

The incidence of FeLV disease has dramatically declined over the past several decades. This is likely due to a combination of the availability of accurate screening tests, improved client awareness of the disease, a change in the lifestyle of the average cat (more cats are kept indoors rather than being allowed to roam freely), and vaccination of at-risk cats.

How often is revaccination necessary?

In the initial vaccination series, two doses of vaccine are administered one month apart, which is necessary to provide strong, lasting immunity. Even so, this immunity will decline over time and periodic revaccination will be necessary. Your veterinarian will advise you about the recommended revaccination schedule based on your cat's lifestyle and needs.

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