Cat leukemia (FeLV) is an infection caused by a virus. It is transmitted through saliva and blood. The disease is fatal in about a third of the cases. It can be a problem in areas with a lot of roaming animals. For cats that come into contact with such animals, annual vaccination against cat leukemia is possible. Again, the vet can best advise if this is useful, but with a breed cat that has grown up in a closed environment and the new caretakers also do not come into contact with foreign cats, this vaccination is completely unnecessary.