[sarpeedo]

Actually this is sort of a thing. For example the polio vaccine has a killed vaccine (analogous to spikes) and a live attenuated vaccine. The live vaccine has higher risk of side effects but provides more robust immunity.

Vaccine schedules can be designed to give the killed version first for some immunity followed by live vaccine to provide more robust immunity.

None of the COVID vaccines so far are live attenuated vaccines as far as I'm aware.