For basic model/math, see: https://academic.oup.com/cid/article/52/7/911/299077
It also provides a good definition of "herd immunity", which is a cumulative incidence of 0 over the lifetime of an unvaccinated individual. I.e., even if you can't get vaccinated, you are extraordinarily unlikely to catch the disease.
That also suggests a good definition for "back to normal" -- to wit, that we go back to our previous chance of catching Covid, zero.
Critical vaccination threshold for herd immunity for a given R0
and E
: