Posted: October 23, 2009, 3 a.m. EDT
Q: I had my cat tested for feline leukemia last year. The test was negative. I don't know how but I missed getting her the vaccine. (I changed vets, for one thing). Is there any reason I cannot get her the vaccine now, without getting her tested again? She is a house cat but we let her outside some. She has not, that I know of, been near any other cat.
A: The feline leukemia vaccine should only be given to cats that initially test negative for the virus. If you vaccinate a cat that you think is negative for the virus, but is actually positive, you won’t do any harm, but the vaccine offers the cat no benefit at all.
Ideally, your cat should be tested for leukemia twice, 90 days apart. Your cat initially tested negative, however, if your cat was exposed to the virus a week or two before the test, your cat would test negative, as it takes a few weeks after exposure before virus can be detected in the bloodstream.
If your cat has not been exposed to any cats during the 90-day period after the initial test, a second negative test proves for certain that your cat is negative, and the leukemia vaccine series can commence. Considering that your cat does go outdoors, and you don’t sound 100 percent certain that she has not encountered another cat, I’d play it safe and have her tested again before vaccinating.