Feline Leukemia Vaccine (FeLV) for Cats

Feline leukemia virus (FeLV) is found in approximately 2 percent of cats in the United States. The disease is found worldwide in varying amounts. FeLV suppresses, or decreases, the immune system making cats more susceptible to a variety of infections and cancer. 

Studies show that cats infected with FeLV live shorter lifespans than cats without it. Because of the effects of this disease, it is important to protect your cat from infection. Vaccination can help with that, but it isn’t necessary for all cats. 

Read below to understand if your cat needs the FeLV vaccine.

What is the FeLV Vaccine?

The FeLV vaccination protects cats against the symptoms of feline leukemia virus. It was first created and placed on the market in 1985. This vaccine has been approved by the United States Department of Agriculture (USDA). Pet parents can go to any veterinary clinic in the country and request the FeLV vaccine. This vaccination is not known to be required by any level of law in the US.

How Does the FeLV Vaccine Work?

After vaccination, a cat’s immune system creates a memory for a specific virus—both by producing cells that fight the disease and by producing immunoglobulins, important proteins that find the virus, stick to it, and signal the body to destroy it. 

If a cat is not vaccinated against a particular virus, his immune system will require days to weeks to mount an effective immune response when he is exposed to it. If, however, a cat IS vaccinated against a particular virus, his immune system will kick in within minutes to hours after exposure!

Some studies have shown that the FeLV vaccine may prevent symptoms (signs) of FeLV disease, but not necessarily infection. Testing of cats exposed to FeLV after vaccination shows the presence of proviral DNA of FeLV in the body. This is not an active infection, and the virus should not replicate or infect the cat. However, it is possible that in future years FeLV could begin to replicate (or grow) and cause FeLV disease. 

There are currently 2 different kinds of FeLV vaccination:

Inactivated virus vaccine: this means the actual virus in its complete form is altered in the laboratory so it can no longer infect cats—also known as “killed” vaccines.

Recombinant canarypox vector vaccine: This means an important piece of FeLV was placed into another harmless virus called canarypox. This live canarypox virus will express important proteins from FeLV that will then stimulate an immune response, but FeLV itself is not present in its entirety

Feline Leukemia Vaccination Schedule for Cats

Before any cat is vaccinated against FeLV, they need to be tested for FeLV. There are a variety of tests, and your veterinarian will choose the exact test based on what his/her clinic uses. If your cat tests positive for an infection, it is not recommended to vaccinate against FeLV. 

Every cat receives two doses for FeLV, 2-4 weeks apart. The duration of immunity—or the length of time that the vaccine protects your cat—is proven at 1 year in most vaccines. Studies have shown that several vaccines can provide 2 years of protection, but not all cats will experience full protection at 2 years. Your veterinarian will help you decide your cat’s level of risk and whether you can wait 2 years until the next vaccination.

Side Effects of the Feline Leukemia Vaccine

As with any cat vaccination, the FeLV vaccination can cause the following side effects:

• Local swelling and/or pain (vaccine should be given in the left rear leg)
• Decreased activity
• Fever of short duration
• Granuloma (non-cancerous growth from chronic inflammation)

In rare cases, cats can develop injection site sarcomas, a severe form of skin cancer that is very invasive and cannot be easily treated. Approximately 1 in 10,000 cats who are vaccinated will develop this disease. Other types of injections can cause this rare disease as well, such as long-acting steroids.

Speak to your veterinarian if you are concerned with this rare side effect. Ask your veterinarian where they inject vaccines in cats. An outdated veterinary practice was to give vaccines to cats in between the shoulder blades, and this is associated with a much higher risk of developing sarcoma. Vaccines should be given low on your cat’s hind leg (usually the left) or on the tail.

Manufacturers of the FeLV Vaccine for Cats

There are four licensed manufacturers of the FeLV vaccine in the U.S. They all create FeLV vaccines alone, as well as some create a combined product with other viruses. Either killed or canarypox vector vaccines are made. 

The following manufacturers make FeLV vaccinations:

Cost of the FeLV Vaccine for Cats

Individual FeLV vaccines will cost approximately $25-$35 each at a veterinary clinic. This does not include the examination fee at each appointment. Your cat will need to be tested for FeLV before receiving his first vaccine, which also generally ranges anywhere from $25-$40.

Does Your Cat Need the Feline Leukemia Vaccine?

Kittens are recommended by feline specialty groups to be routinely vaccinated against FeLV since they are most susceptible to contracting FeLV. Not every kitten will have exposure, however, so not every veterinarian will recommend vaccination of your kitten. 

After the first round of FeLV vaccination (2 boosters), whether or not your cat should be vaccinated 1 year later depends on if there is any potential for exposure to FeLV. Adult cats build natural immunity to the FeLV disease, so vaccinating adult cats should only occur if there is substantial risk of exposure to FeLV. 

Possibilities for FeLV exposure include:

• If your cat goes outdoors.
• If your cat spends considerable time on porches or at screened windows and comes into close contact with roaming cats/
• If you decide to adopt or purchase a new cat that is either FeLV infected or has not been tested.
• If you foster (temporarily care for) any cat whose status of FeLV infection is unknown.
• If your cat goes to cat shows.
• If you routinely board your cat.

Your veterinarian can help you determine whether your cat should be vaccinated against FeLV.