See: https://www.news-medical.net/news/20200731/Research-suggests-New-York-City-may-have-reached-coronavirus-herd-immunity-threshold.aspx https://www.news-medic

See: https://www.news-medical.net/news/20200731/Research-suggests-New-York-City-may-have-reached-coronavirus-herd-immunity-threshold.aspx https://www.news-medical.net/news/20200731/Research-suggests... In addition to immunity based on T cells, the HIT depends on how individuals are networked. The original 60-70% estimates were based on 100% of people being vulnerable and also a random distribution of individuals interacting. In reality a small fraction of the population will have many interactions and once they become immune those transmission vectors away and the average R number drops. So based on the latest research plus observations of the worst hit places, 20-25% seems plausible.