If a kitten or cat goes down with the herpes cats 'flu, then once they get over the initial bout of the disease, it can come back again whenever the cat has gone through a traumatic experience like re-homing or neutering. Kittens can get it as well as adults. It never leaves the cat's body but lies dormant until under stress. That is why it is best to get kittens vaccinated at 9 and 12 weeks of age. This will help protect them against the major killer cat flu viruses that they may meet. I say 'help' protect...... as in all vaccinations, there is always a verysmall percentage of cats that will not respond to vaccination......... like in humans. However, the vaccination covers the most dangerous strains of cat 'flu but cannot cover all strains so although your kitten or cat is vaccinated, is can, although rarely, catch a weaker strain of cat 'flu. Once again, it is similar to the human 'flu vaccinations. There are far too many types of 'flu out there. Wouldn't it be great if we could have a vaccination for all viruses.