Cats who are infected with feline immunodeficiency virus (FIV) may not show symptoms until years after the initial infection occurred. Although the virus is slow-acting, a cat’s immune system is severely weakened once the disease takes hold. This makes the cat susceptible to various secondary infections. Infected cats who receive supportive medical care and are kept in a stress-free, indoor environment can live relatively comfortable lives for months to years before the disease reaches its chronic stages. Cats with FIV can be treated with the following vaccines: Fel-O-Vax FIV and Fel-O-Vax LvK + FIV.