I would, as a practitioner, recommend yearly blood titers (tests to analyze the level of protection) to
determine the duration of immunity as a safe guard to assure proper protection for your cat.
[18] See page 7 under «Serological Testing to
Determine the Duration of Immunity (DOI)» in Day, M.J., Horzinek, M.C., Schultz, R.D. World Small Animal Veterinary Association's (WSAVA) Guidelines for the Vaccination of Dogs and Cats.