Cat getting feline leukemia vaccine

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As a cat owner, you want your furry little pet to be healthy, and that means following age-specific care recommendations, including vaccines. Cats face a number of health threats, but as kittens, they are particularly vulnerable. One devastating disease is the feline leukemia virus, or FeLV, which is a highly contagious disease among cat species and is incurable. There is a vaccine, and while it isn't 100 percent effective, veterinarians recommend vaccinating your kitten against the disease.

In this post, we’ll define FeLV, explain how the vaccine works, and when vaccination is recommended.

What Is Feline Leukemia Virus (FeLV)?

Feline leukemia virus, or FeLV, is an incurable and contagious disease that can cause problems with cancers, immune system issues, anemia, and early death. Laboratory tests have shown that FeLV is potentially contagious to several other species.

FeLV is one of the major causes of death for cats, and in fact, it's the cause behind a majority of cat deaths from viruses; about 50 percent of cats known to have FeLV will die from the disease in just over two and a half years after diagnosis.

FeLV spreads easily through contact with body fluids and secretions from an infected cat, including milk, saliva, mucus, and anything you find in the cat's litter box. This means cats can acquire the virus merely through being groomed by another cat, or by sustaining a scratch or bite during play with other cats. Because kittens like to play, scratch, and lick each other, and can be exposed to adult cats' saliva and milk, vets recommend vaccinating kittens for FeLV before they turn one year old.

Cat getting pet by owner


As with many cat-disease symptoms, FeLV can manifest in a number of ways that initially mimic many other diseases. It is possible for an infected cat to show no symptoms for a while, which is why it's especially important to have cats and kittens tested for FeLV if you find strays.

Common symptoms include:

  • Loss of appetite
  • Progressive weight loss
  • Poor coat condition
  • Enlarged lymph nodes
  • Persistent fever
  • Pale gums and other mucus membranes
  • Inflammation of the gums (gingivitis) and mouth (stomatitis)
  • Infections of the skin, urinary bladder, and upper respiratory tract 
  • Persistent diarrhea 
  • Seizures, behavior changes, and other neurological disorders
  • A variety of eye conditions
  • Abortion of kittens or other reproductive failures
Graphic outlining symptoms of FeLV

How Does The Feline Leukemia Vaccine Work?

Cats are encouraged to get a series of vaccinations for specific conditions when they’re adopted into a new home. Some of these vaccines are called core vaccines, which are highly recommended for kittens and any cat whose vaccination history is unknown (for example, an adult stray that you find and adopt). Non-core vaccines are recommended but optional; whether or not you have your cat get this vaccine depends on the animal's risk factors (for example, living in an area where a particular disease is a real problem).

The FeLV vaccine is considered a non-core vaccine, however, most vets suggest that cats younger than one-year-old are vaccinated, while older cats are less at risk. The American Association of Feline Practitioners (AAFP) recommends having kittens vaccinated fully (two doses) against FeLV with a booster after one year. Future boosters are also an option, given the environment, the cat is in.

AAFP recommends having kittens vaccinated fully (two doses) against FeLV with a booster after one year.

With adult cats, determining whether or not to vaccinate for FeLV depends on how likely it is that they'll come into contact with infected cats. If the risk seems high, such as for a cat that likes to roam outside or one who keeps escaping your house, then vaccination is recommended. Vaccination may not be suitable for all cats because vaccinations in some cats have led to sarcomas developing at the injection site. This isn't a huge risk, but cat owners should consult their vet about their cat’s suitability for the FeLV vaccine and other vaccinations.

Note that if you have a lot of cats, such as having resident and foster cats in the same house, then your resident cats should be vaccinated against FeLV, especially if you foster a FeLV-positive cat. That being said, you should still isolate infected and uninfected cats from each other because the vaccine isn't 100 percent effective. 

When Are Cats Vaccinated For FeLV?

The FeLV vaccination is a two-dose series with a booster. The first dose should be given to kittens between eight and 12 weeks old with the second dose given three to four weeks after that. The booster is given one year after the second dose of the original sequence. Any other yearly boosters after that depend on the cat's risk of exposure to FeLV.

Remember that the vaccine is only helpful for cats who aren't infected, so the cat must be tested for FeLV prior to vaccination, and then again before the second and booster shots if the cat may have been exposed to the virus.

Is The FeLV Vaccine Safe?

Any vaccine carries the risk of side effects. Mild side effects for the FeLV vaccine include swelling at the site of the injection, or the risk of an allergic reaction. A more serious side effect, and the reason that vaccines in cats are limited, is sarcoma. A sarcoma is a type  of cancerous tumor that can form at any injection site, but is more common with vaccines. Unfortunately, it can take a decade before the sarcoma appears. Again, this is why vets are so cautious about vaccines for cats. However, the risks from the diseases the vaccines fight against are severe enough that it's worth getting the cat vaccinated, despite the risk of sarcoma.

Is The FeLV Vaccine Effective?

The vaccine may not be 100 percent effective, but it is effective enough that most vets recommend that kittens receive the full series of FeLV shots.

Should I Vaccinate My Cat For FeLV?

If you have a kitten, it's highly recommended that the kitten receive the full series of shots for FeLV. For your older cats, if they haven't been vaccinated, speak with your vet as they can determine the risk the cat faces.

Graphic with FeLV prevention tips

FeLV Prevention

There is currently no cure for FeLV, only treatments that focus on the individual problems that FeLV can cause, such as treating an infection. Prevention is the best way to ensure your cat doesn't end up with FeLV, which means both vaccination and keeping infected and uninfected cats separated from each other. Keep cats indoors, or provide a specific, enclosed place outside so that cats can be outside without wandering about and possibly getting infected.

Never bring a cat into your home without testing it for FeLV; if you're in a situation where you've rescued a cat, keep it isolated until you've had it tested. This isolation includes ensuring uninfected cats don't share the new cat's food and water bowls or litter box. If you've already let a new cat mingle with your resident cats, then you need to have all the cats tested for FeLV.

Because cats can join your home at any time, it really is recommended that you have kittens vaccinated and speak to your vet about whether your adult non-vaccinated cats need to get the vaccine as well.

Final Notes

Feline leukemia virus can lead to several serious health conditions and even early death for infected cats. Thus, protection against the disease is essential. Speak to your vet about the FeLV vaccine to determine whether it’s a fit for your feline friend. 



  1. Levy, Julie K., and Amanda Burling. “Feline Leukemia Virus and Related Diseases in Cats - Overview - Generalized Conditions.” Merck Veterinary Manual, Merck Veterinary Manual, 15 Dec. 2021,

  2. “Feline Vaccines: Benefits and Risks.” Cornell University College of Veterinary Medicine, 23 July 2018,

  3. “Feline Leukemia Virus.” Cornell University College of Veterinary Medicine, 19 Aug. 2021,

  4. Primary Series- Vaccine Kittens (< 16 Weeks ... -

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