Pretty much everything puts evolutionary pressure on the virus. If the host keels over 1s after infection, that line's going to die out. If the antibodies from vaccination/infection target an invariant portion, the virus might effectively die out (polio, measles, etc). Ideally, between vaccination and infection we've proceeded to an equilibrium - the nasties have been outcompeted or died out and (way) fewer people have been keeling over. If/when Covid truly behaves like the flu it will be another of the coronaviruses causing colds of varying severity.
