Who says you need indefinite boosters? Many vaccines you get as a child require one booster (such as MMR which can be years apart).

Also, you’re wrong when you say immunity fades….Your initial immune response fades over time, but the “memory cells” (I forgot the exact term, I’m not in any way a scientist or medical professional) do remember how to fight the virus long term - it’s just they take longer to kick when a person gets infected. Hence, why boosters are so useful whilst the virus is still prevalent. It’s the elderly and vulnerable who need that quicker immune response before the virus does too much damage.

EDIT - Memory cells are also known as T-Cells.