Kittens are generally vaccinated against FeLV around 8 to 9 weeks of age. A booster vaccination is given 3 to 4 weeks later, according to the vaccine label, followed by boosters each year as long as the risk for exposure remains. Similarly, vaccination against FIV can begin when kittens are around 8 weeks of age. Two additional boosters are given 2 to 3 weeks apart, followed by boosters each year as long as the risk for exposure remains. Cats that go outside are at greater risk for exposure to FeLV and FIV compared with cats that stay indoors.