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The FeLV vaccine, which protects against feline leukemia virus, is recommended for every kitten and for adult cats with a risk of exposure, like cats who go outdoors or live with cats of unknown status. For an adult cat who lives strictly indoors with no contact with other cats, it's usually optional, and your vet will weigh it with you.
Kittens come first because they're far more likely than adults to end up with a lasting infection after exposure.
Below we cover how FeLV spreads, why every cat should be tested before joining a home, which cats benefit most from the vaccine, and what it can and can't do. Your vet decides the right plan for your cat.
What is feline leukemia virus?
FeLV is a retrovirus that can become part of a cat's own genetic material and may never be fully cleared. The Cornell Feline Health Center estimates that about 2 to 3 percent of cats in the United States and Canada are infected, rising as high as 30 percent among ill or high-risk cats. Rates have fallen over the past 25 years, thanks to vaccination and better testing.
That's the hopeful part. The harder part is that many infected cats look perfectly healthy at first. Over weeks to years, Cornell lists signs like weight loss, a poor coat, enlarged lymph nodes, persistent fever, pale gums, mouth inflammation, repeated infections and diarrhea, and gives a median survival time of 2.5 years after diagnosis.
How does FeLV spread between cats?
Mostly through close, lasting contact. Infected cats shed the virus in saliva, feces, urine and milk. Cornell names bite wounds from fights, mutual grooming, shared food bowls and litter boxes, and passing from mother to kitten before birth or while nursing.
The virus survives only a few hours outside a cat's body, so Cornell says infection without prolonged close contact is unlikely. A cat who glares at the neighbour's tabby through the window isn't really at risk. A cat who scraps with that tabby in the laneway is. That's why your cat's lifestyle matters so much in the vaccine decision.
Who needs the FeLV vaccine?
Every kitten needs the FeLV vaccine, and adults need it when they have real contact with other cats. Here's how the recommendations line up:
| Cat | FeLV vaccine | Source |
|---|---|---|
| Kitten under one year | Recommended (core) | Cornell, WSAVA |
| Adult with outdoor access | Recommended | Cornell, WSAVA where FeLV is common |
| Adult living with an FeLV-positive cat or cats of unknown status | Discuss with your vet | Risk depends on contact |
| Adult strictly indoors, no contact with other cats | Usually non-core | Cornell |
Cornell calls FeLV a core vaccine for kittens and recommends it for cats at risk of exposure, such as indoor-outdoor cats. For adults, its vaccine guidance treats FeLV as non-core, depending on whether a cat could be exposed to infected cats. The World Small Animal Veterinary Association lists FeLV as core for cats under one year and for outdoor cats where the virus is common.
Every kitten should be vaccinated against FeLV. For adults, the decision follows the cat's real contact with other cats.
Why are kittens a priority?
Kittens are a priority because their immune systems are still developing, and Cornell says kittens exposed to FeLV are at much higher risk of a progressive infection than adults. There's a practical reason too. Plenty of kittens end up with more outdoor access, or a new feline housemate, later than their owners ever planned. A vaccinated kitten is covered if life changes.
Why test before vaccinating?
Because the vaccine doesn't help a cat who's already infected, and an infected cat needs a different plan. Cornell recommends testing all cats for FeLV before they join a household. No single test is conclusive, so a positive screening result gets confirmed, and testing may be repeated after 3 to 6 weeks if exposure was recent.
Cornell also notes that FeLV vaccines don't cause false positives on FeLV tests, so a vaccinated cat can still be tested accurately later on.
What the FeLV vaccine cannot do
The FeLV vaccine can't guarantee protection, treat an infected cat or replace testing. Cornell says it doesn't protect every vaccinated cat, so limiting exposure still matters, and new cats should still be tested before they meet your current ones.
Cornell calls keeping cats indoors the most reliable prevention. If your cat goes outside, supervised time on a harness or a secure catio lowers the risk of fights and contact with unknown cats.
Like all feline vaccines, this one carries a small risk of side effects. Cornell's vaccine guidance says short-term reactions are mainly allergic, and that a tumour at the injection site is an uncommon long-term risk. If your cat has trouble breathing or seems very unwell after a vaccine, go to a vet or emergency clinic now.
Plan it with your vet
Bring an honest picture of your cat's life: the balcony, harness walks, boarding, any new cats, the neighbour's cat at the window screen. Our guides to the FVRCP vaccine and core vaccines for cats cover the rest of the plan.
Afterwards, add each dose to your cat's pet records in the free PetGrid app, and a reminder makes itself from the next due date.
Perguntas frequentes
Does my indoor cat need the FeLV vaccine?
Usually not as an adult, if your cat never goes out and has no contact with other cats. Kittens should get it, and Cornell recommends it for adults at risk of exposure, so ask your vet about your cat's situation.
Is the FeLV vaccine core for kittens?
Yes. Cornell and WSAVA both treat FeLV as a core vaccine for kittens, because kittens are much more likely than adults to develop a lasting infection.
Should my cat be tested before the FeLV vaccine?
Yes. Cornell recommends testing all cats before they join a household, since the vaccine doesn't help a cat who's already infected.
How is feline leukemia spread?
Through close contact: bite wounds, mutual grooming, shared bowls and litter boxes, and from mother to kitten. The virus survives only a few hours outside a cat's body.
Is the FeLV vaccine 100 percent effective?
No. Cornell says it doesn't protect every cat, so keeping exposure low, for example by limiting contact with unknown cats, still matters.
My cat lives with an FeLV-positive cat. What should I do?
Talk to your vet about testing and vaccinating the negative cat, and about cutting down on shared bowls, litter boxes and grooming. Cornell lists mutual grooming and shared bowls and litter boxes among the ways FeLV spreads, and notes that the vaccine doesn't protect every cat.
Em resumo
The FeLV vaccine is a must for kittens and a sensible choice for adult cats who go outside or meet cats of unknown status. Test first, vaccinate for the risk your cat really has, and keep exposure low, since no vaccine is perfect.
Keep your cat's test results and vaccine dates together, so the next vet visit starts with the full picture. The PetGrid app is free for pet owners.
Guarde os registros, as vacinas e as consultas do seu pet em um só lugar seguro. O app PetGrid é gratuito para tutores, com ou sem clínica.
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