Guys, do indoor cats REALLY have to get shots every year?

Guys, do indoor cats REALLY have to get shots every year?

...or is this just another way for vets to make money?

Will Bobby asplode if I don't take her to the vet every year?!?!

Bobby is a strictly indoor cat and so is her sister. Someone I know who worked as a vet tech said that indoor cats really don't need to go to the vet regularly after their initial visit.

I don't feel like asking Google, DVM because it gives me confusions...I trust the cat owners of GT for some solid answers!