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Feline Leukemia (FeLV) Vaccines for Cats: A Complete Guide (Vet Answer)

Written by: Dr. Joanna Woodnutt BVM BVS (Veterinarian)

Last Updated on January 12, 2024 by Catster Editorial Team

Veterinarian giving injection to cat

Feline Leukemia (FeLV) Vaccines for Cats: A Complete Guide (Vet Answer)


Dr. Joanna Woodnutt Photo


Dr. Joanna Woodnutt

MRCVS, Veterinarian

The information is current and up-to-date in accordance with the latest veterinarian research.

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To ensure your cat stays healthy for many years to come, vaccines are an important way of contributing to your cat’s medical care. This means that, in addition to a yearly or twice-yearly physical exam with their vet, they may also need vaccines.

All cats receive regular vaccines, called “core” vaccines, that are considered essential for all cats. Depending on a cat’s lifestyle, such as whether they are exclusively indoors, if they also spend time outside, or how often they board around other cats, they may need additional vaccines. Feline leukemia vaccines fall into the latter category. For indoor-only cats, may only receive FeLV vaccines during their kitten series. For cats that routinely spend time outside, they may get a FeLV vaccine throughout their lifetime.

Feline leukemia virus is a serious disease, that can lead to lifelong immune suppression and fatality. Some cats do not develop full-blown illness, and some are even able to fight off the virus. However, vaccination can help prevent illness in many cats, and due to the risks involved once the virus is contracted, having your cat vaccinated is sensible if they are in a high-risk category.

Read on to learn more about the feline leukemia virus, the disease, and the vaccine.

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What is Feline Leukemia Virus (FeLV)?

Feline leukemia virus is a type of virus that can cause cancer in cats, in the way that it infects and replicates. It targets cats only, which means humans and dogs are not susceptible to the virus. After being exposed to the virus, a cat may mount an immune response and clear the virus, or may become persistently infected.

Once infected, the virus impacts the bone marrow in many cats, leading to trouble with the production of red and white cells. This can cause anemia, immunosopression, and cancer. The virus is then spread through bodily secretions, particularly saliva, which means that other cats in contact with an infected cat, particularly those that may groom one another, are at risk of being exposed to the virus.

The virus does not live long outside the body, so inanimate objects are not thought to be a major source of infection.

What Are Risk Factors for Feline Leukemia Virus?

thin cat with yellow eyes
Image Credit: Anastasiya Tsiasemnikava, Shutterstock

Risk factors for feline leukemia include going outdoors, living with other cats infected with FeLV, living in a cattery or multi-cat household, or having spent time as a stray. As cats get older, it is believed that their immune systems are better able to fight off FeLV infections. Therefore, being a younger cat may also be considered a risk factor.

Where Are the Symptoms of Feline Leukemia Virus in Cats?

Symptoms of feline leukemia virus can include:
  • Weight loss
  • Loss of appetite
  • Enlarged lymph nodes
  • Pale gums and paw pads
  • Poor haircoat
  • Rapid breathing
  • Lethargy
  • Inflammation of the mouth

As the above symptoms are generally quite serious, if you are concerned about seeing any of the above symptoms, it is best to get your cat to a vet as quickly as possible. It may also be advisable to ask your vet if you should isolate any sick cats from healthy cats, to prevent potential spread of the virus.

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Frequently Asked Questions (FAQs)

What is a typical feline leukemia vaccine schedule?

Generally, feline leukemia vaccines are given as a primary series, consisting of two vaccines, 3-4 weeks apart. After this, they are given no more frequently than annually, and sometimes much less. If your cat is indoors only, and at low risk of being exposed to the virus, they may not receive a feline leukemia vaccine at all, at the discretion of your vet.

Veterinarian at vet clinic giving injection to cat
Image Credit: Tom Wang, Shutterstock

What are possible FeLV vaccine side effects?

The most common side effect for vaccines in cats tend to be lethargy, followed by vomiting or diarrhea. Cats rarely develop anaphylaxis, or life-threatening allergic reactions to vaccines, facial swelling, or hives—as many other species are prone to after receiving vaccines. Let your vet know if your cat does have any odd reactions to a vaccine, as this may change how they are vaccinated in the future.

However, vaccines can also have rare (but serious) side effects. One of the more serious side effects, particularly in cats, is called a vaccine-associated fibrosarcoma. This is a type of cancer that forms from the cells that form the connective tissue layer under the skin. There is strong evidence to suggest that a combination of genetics, along with certain vaccines, have led to the formation of these cancers in cats. Many of these vaccines are now made in a different manner, so as to not contain adjuvant, and most vaccines in cats are also now given in specific locations of the body—so that if one of these cancers occurs, it can be known which vaccine may have played a role.

Does my indoor cat need a feline leukemia vaccine?

Indoor cats are not exempt from contacting feline leukemia virus, however they are at very low risk. Speak to your vet and discuss if it is an appropriate vaccine for your cat’s lifestyle. Many vets will not vaccinate indoor-only cats for feline leukemia, especially after their initial kitten series.

cat blood test
Image Credit: PRESSLAB, Shutterstock

How is feline leukemia diagnosed in cats?

Feline leukemia is often suspected based on a cat’s clinical signs of illness, as well as their age. However, blood tests are needed to confirm viral infection. Vaccination does not interfere with such testing. The most common tests check for portions of the virus’ genetic code in blood, and is a good screening tool if FeLV infection is suspected. However, it is quite sensitive. So, if positive, additional testing is usually recommended to confirm the result.

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Feline leukemia is a preventable disease in household cats, through vaccination and reduction of risk factors in their environment. The vaccine is helpful in preventing the disease, but may not be needed in all cats, especially if they are not at high risk of being exposed to the virus, or to infected cats. Speak to your vet to determine whether or not your cat is a candidate for the vaccine, depending on their lifestyle.

Featured Image Credit: Africa Studio, Shutterstock

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