Taken from FAB SITE
With most vaccines, the protection they provide against infection is not lifelong and therefore further ?booster' injections are usually required to maintain good protection. Cats should receive their first booster injection a year after the kitten vaccines are given. Subsequent annual booster injections are usually advised for at least some diseases and currently most manufacturers can only prove that their vaccines are effective for a year. However, some vaccines appear to induce protection that lasts much longer than a year. Some vets therefore advise less frequent booster vaccinations, often every three years subsequently, at least for panleucopenia virus and the cat ?flu viruses (unless there is a particular risk of infection). Talk to your vet about what is best for your cat in your area.
PLEASE REMEMBER THAT CATTERIES INSIST ON YEARLY BOOSTERS.