If R0 is truly 5.7 - roughly 82.46% of the population must become immune before “herd immunity” kicks in.

((R0 − 1)/R0) is known as the “herd immunity threshold” — that is, with an R0 value of 5.7 the computation would be ((5.7 - 1)/5.7) or 82.46%

Learn more here, — “Herd Immunity”: A Rough Guide: https://academic.oup.com/cid/article/52/7/911/299077#3862683

As a comparison, here are the R0 values of other well-known infectious diseases: https://en.m.wikipedia.org/wiki/Basic_reproduction_number