Yes, there is a vaccine for feline leukemia virus (FeLV), and it’s considered a core vaccine for all kittens under one year old. Several versions are available, and in clinical studies the most effective ones prevented persistent infection in about 93% of vaccinated cats. The vaccine won’t help cats already infected, so testing before vaccination is essential.
How Well the Vaccine Works
In a controlled study comparing three commercial FeLV vaccines head to head, researchers vaccinated groups of 20 cats each, then deliberately exposed them to the virus. In the unvaccinated placebo group, 75% of cats developed persistent infection. Among the two best-performing vaccines, only 1 out of 20 cats (5%) in each group became persistently infected, translating to a 93% prevention rate. The third vaccine still performed well at 80% protection.
No vaccine offers 100% protection. That 93% figure means the vast majority of vaccinated cats will fight off the virus if exposed, but a small number can still become infected. This is why vaccination works best as one layer of protection alongside limiting contact with cats of unknown FeLV status.
Which Cats Should Get It
All kittens should receive the FeLV vaccine. Kittens are more vulnerable than adult cats because their immune systems are still developing, making them more likely to develop a lasting infection if exposed. The 2024 WSAVA vaccination guidelines classify FeLV vaccination as core for cats under one year old and for any adult cat that goes outdoors or lives with cats that do.
For adult cats that live strictly indoors with no exposure to cats of unknown status, the vaccine is considered optional. But “indoor only” deserves an honest assessment. If there’s any chance your cat could slip outside, encounter a new cat brought into the home, or be exposed to a stray through a window screen, vaccination is worth discussing with your vet. UC Davis specifically recommends vaccinating any indoor cat that might be exposed to cats of unknown FeLV status, including when introducing a new cat to the household.
Testing Before Vaccination
Your cat needs to test negative for FeLV before receiving the vaccine. This is a simple blood test your vet can run in the office, often with results in minutes. The reason is straightforward: the vaccine has no therapeutic value for cats already carrying the virus. Vaccinating an infected cat won’t clear the infection or slow the disease. It would simply be an unnecessary injection.
The Vaccination Schedule
Kittens can start the FeLV vaccine series as early as 8 weeks of age. The initial series requires two doses given 3 to 4 weeks apart. A booster follows one year after the last dose of that initial series.
After that first-year booster, the schedule depends on your cat’s risk level. Cats with ongoing high exposure (outdoor access, multi-cat households with cats that go outside) should be revaccinated annually. Cats at lower risk can be revaccinated every 2 to 3 years, depending on the specific product your vet uses. If your cat’s lifestyle changes, say you move from a house with outdoor access to a high-rise apartment, the booster schedule can be adjusted accordingly.
Vaccine Types and Safety
Two main types of FeLV vaccine are available: recombinant vaccines and inactivated (killed virus) vaccines. Recombinant vaccines use a piece of the virus’s genetic material delivered through a harmless carrier virus, while inactivated vaccines use whole killed virus particles. Both types are effective.
One important distinction is whether a vaccine contains an adjuvant, a chemical additive that boosts the immune response. Adjuvanted vaccines have been linked to a rare but serious complication: injection-site sarcomas, a type of tumor that can develop where the shot was given. The risk is low, occurring in roughly 1 cat per 10,000 to 30,000 vaccinations, but it’s not zero. Non-adjuvanted vaccines were developed partly to reduce this risk. A newer non-adjuvanted option available in Europe also uses a smaller injection volume (0.5 mL instead of 1.0 mL), which produces less local inflammation at the injection site.
Because of the sarcoma concern, current guidelines recommend giving FeLV vaccines in specific locations on the body, typically a hind leg rather than between the shoulder blades. If a tumor were to develop in a limb, surgical removal is far more feasible than in the trunk area. This is a precaution, not a reason to skip vaccination. For cats at risk of FeLV exposure, the benefit of preventing a fatal viral infection far outweighs the very small chance of an injection-site reaction.
How FeLV Spreads
Understanding transmission helps explain why certain cats need the vaccine more than others. FeLV spreads through close, sustained contact between cats. Mutual grooming, sharing food bowls and litter boxes, and bite wounds are all common routes. An infected mother cat can also pass the virus to her kittens before birth or during nursing.
The virus doesn’t survive long outside a cat’s body, typically less than a few hours under normal household conditions. Casual or brief contact is unlikely to transmit it. The cats at highest risk are those living with an infected cat, those allowed outdoors unsupervised where they could encounter strays, and kittens born to infected mothers. If your cat has zero contact with other cats and truly never goes outside, exposure risk is minimal, but the kitten series is still recommended as a safety net during the most vulnerable stage of life.