Please don't shoot me down in flames; I'm aware that what I'm about to say is controversial. I have my cats initially vaccinated, but not boostered. Sam and Polly were only given flu and enteritis vaccinations by the rescue from which I had them; I've had Fred and Vic given flu, enteritis and Felv vaccines, but, like P and S, they won't be boostered.
I've come to the conclusion that, provided a cat goes out, it will probably meet a cat who is infected, thereby naturally boostering their immunity. Even if this doesn't occur, I believe that the annual boostering weakens a cat's immune system. I base this purely on experience. Before Polly and Sam, every cat I had was regularly boostered but died young. P and S have (touch wood) lived to a grand old age.
I wouldn't necessarily recommend others do this, but just that the issue is given some thought before automatically giving annual jabs. For anyone new to cat care: don't do as I do, become experienced first. Take the advice of your vet.