Originally Posted by Willowy
Cats over 18 months of age have about a 90% immunity to FeLV (and the shot give less immunity than that)
Having lost a 3 year old cat to FeLV, and doing a lot of digging into the disease, I have to say that this is absolutely not true. I consulted with a cat specialist who is involved with current ongoing university research into FeLV. An unvaccinated adult cat has about a 25% - 30%
immunity to FeLV. Kittens born with it or exposed prior to vaccinations have a 95%+ fatality rate, which means they have a 5% or less immunity.
Some positive kittens don't test as positive until they are a few months old. If you bring a new kitten into your house with FeLV and your resident cats aren't vaccinated, you are risking their lives.
I don't want people on this site to get a false sense of security about FeLV. If your cat goes outside, is exposed to outside cats, or is exposed to new cats in your household, they should be vaccinated. Regardless of age.