Cats are routinely vaccinated against the “cat flu” viruses, a combination of different viruses that give the symptoms of cat flu such as eye infections and sneezing and enteritis, which causes severe diarrhoea. They can also be vaccinated against Feline Leukaemia Virus, a disease that attacks the immune system. Kittens can be vaccinated from nine weeks of age and require a course of two injections initially with an annual booster to maintain immunity.