I'm aware of the 3 dose vaccines - what I'm asking is if there's any connection between the duration and the type of vaccine and the type of underlying virus.

I'm aware of the 3 dose vaccines - what I'm asking is if there's any connection between the duration and the type of vaccine and the type of underlying virus. The flu, for example as existed longer than COVID and we do not have a "3 dose" vaccine that prevents the flu for a decade. Why would we expect this for COVID as opposed to an annual booster?