Contrary to what its name implies, feline leukemia (abbreviated as FeLV or sometimes referred to as “feleuk”) is not a blood cancer – although it can cause cancer affecting the blood. Instead, it is a viral infection that can set up shop anywhere in a cat’s body. Once a cat contracts the virus, it cannot be cured, but keeping a cat current on his vaccinations will prevent disease associated with FeLV. Though it is not a core vaccine, it is recommended for cats at risk for exposure to this dangerous disease.


Feline leukemia virus is moderately contagious, generally transmitted when a cat comes into contact with saliva from an infected cat (via social behaviors, such as mutual grooming and sharing food or water bowls). In-utero , mother-to-kitten transmission can also occur.

Because FeLV can affect almost any organ system in the body, clinical signs can vary significantly. In fact, some cats can seem perfectly healthy, but retain the ability to transmit the disease to others.

Vaccine Characteristics

Though it’s considered a non-core vaccine, this vaccine is highly recommended by the American Association of Feline Practitioners for all kittens.

Ideally, cats should be tested for FeLV infection before their initial vaccination and when there is a possibility that they have been exposed to FeLV since they were last vaccinated. Only FeLV negative cats should be vaccinated.


This vaccine is administered both as an injectable and transdermal vaccine.

Recommended Schedule

While your veterinarian is always in the best position to advise you on individual vaccination decisions, according to the American Association of Feline Practitioners’ 2006 vaccination guidelines, the FeLV vaccine is recommended according to the following schedule:

  • For kittens, an initial dose as early as 8 weeks of age is recommended, depending on product; a second dose should be administered three to four weeks later.
  • For adults and kittens over 16 weeks of age receiving vaccination for the first time, two doses, three to four weeks apart are recommended.
  • When indicated, a single dose is given one year following the last dose of the initial series, and then annually in cats determined to have a sustained risk of exposure.


Administering a vaccine is a medical procedure, and there are times when a vaccine may not be recommended. For example, your veterinarian may advise against vaccinating an animal that is currently sick, pregnant, or may not have adequate immune system functioning to respond to a vaccination. For pets with a previous history of vaccine reactions, the potential risk of a future vaccine reaction should be weighed against the potential benefits of vaccination. These and other issues are evaluated when deciding what is best for your pet.


There is no known alternative to annual FeLV vaccination for cats with sustained risk of exposure to the virus.

Because FeLV is transmitted through contact, keeping sick cats separated from healthy cats can reduce the likelihood of transmission. Any new kitten or cat being introduced into the home should be examined by a veterinarian as soon as possible and separated from all other household pets for a quarantine period. During that time, the new cat should be tested for FeLV and monitored closely for any signs of illness. Any problems should be reported to your veterinarian before introducing the new cat to your other pets.


American Association of Feline Practitioners’ vaccination guidelines

Cornell University College of Veterinary Medicine 

This article has been reviewed by a Veterinarian.