Understanding the FeLV Vaccine for Cats
The feline leukemia virus (FeLV) is a serious threat to cat health worldwide, causing immune suppression, anemia, and cancers like lymphoma. Because there's no cure once a cat is persistently infected, prevention through vaccination is crucial.
What Is FeLV?
FeLV infects only cats and ranks among the leading causes of illness and death in felines. The virus weakens the immune system, leaving cats vulnerable to infections, blood disorders, and certain cancers. Transmission typically occurs through saliva—during grooming or biting—or by sharing food bowls. Kittens can also contract it from their mothers via nursing or the placenta. Extended close contact is usually necessary for spread, so indoor-only cats with no exposure risk are less likely to be infected.
Why Vaccinate Against FeLV?
Since there's no cure for persistent FeLV infection, prevention is vital. The average lifespan after diagnosis drops to less than three years, even with supportive care. Vaccination remains the most effective method to protect at-risk cats from this devastating virus.
Who Should Get the FeLV Vaccine?
- Kittens: All kittens should receive the FeLV vaccine as part of their core vaccinations. Initial doses are typically given between 8 to 12 weeks of age, followed by a booster 3–4 weeks later.
- At-risk adults: Adult cats that go outdoors, live with other cats of unknown status, or might be exposed should be vaccinated and receive regular boosters as advised by a veterinarian.
- Indoor-only adults: For adult cats kept strictly indoors with no risk of exposure, FeLV vaccination is considered non-core and may not be required after the initial kitten series.
How Effective Is the Vaccine?
The latest FeLV vaccines offer high protection rates—some studies show over 85% effectiveness in preventing persistent infection. Newer vaccines using RNA-particle technology provide robust immunity lasting at least two years after the recommended two-dose series.
Testing Before Vaccination
Cats should be tested for FeLV before being vaccinated, especially if their infection status is unknown. There's no benefit in vaccinating a cat that's already infected.
Booster Recommendations
- Cats at ongoing risk (outdoor access or multi-cat homes) should get annual boosters.
- Your veterinarian will tailor booster schedules based on your cat's lifestyle and exposure risk.
Potential Side Effects
No vaccine is completely without risks. Most side effects are mild—soreness at the injection site, fever, or lethargy—and resolve on their own. In rare cases, injection-site sarcomas (a type of cancer) have been linked to vaccines; however, this risk remains low compared to the benefits of protection against FeLV for at-risk animals.
Lifestyle Considerations
- If your cat goes outside or lives with other cats whose health status you don't know, vaccination is strongly recommended.
- Cats kept strictly indoors with no exposure generally do not need ongoing boosters after kittenhood unless circumstances change.
The Impact of Vaccination Programs
The incidence of FeLV has declined over recent decades thanks to widespread vaccination campaigns, improved testing protocols, and more owners keeping their pets indoors. However, FeLV still poses a significant threat wherever unvaccinated or outdoor-access cats are present—especially in multi-cat environments or shelters.
Summary: Protecting Your Cat
- Test new or at-risk cats for FeLV before introducing them into your home or vaccinating them.
- Vaccinate all kittens according to veterinary guidelines; continue boosters for at-risk adults as needed.
- If your cat's lifestyle changes (e.g., they start going outdoors), consult your vet about resuming vaccinations.
The FeLV vaccine, when used appropriately alongside testing and responsible pet management (like keeping vulnerable cats indoors), provides effective protection against one of the most serious feline diseases known today.
