The virus can often remain hidden.
Kittens seem to be at the highest risk for harboring the virus.
The virus might remain hidden for years, or it might never surface. In our case, we are certain that the litter of kittens we took in was infected from their mother. The last cat we have lost track of. The virus can remain hidden for a varied amount of time. Before your cat receives the booster shot the vet needs to run the FeLV test.