This relationship is most readily observed in the following figure.

As ρ increases (darker reds), then a higher proportion of the population is still susceptible.

As ρ decreases (yellow), then over 50% of the population (!) has been infected. pic.twitter.com/0PwIxGIHoo

— Natalie E. Dean, PhD (@nataliexdean) March 24, 2020

○ Oxford Model: Coronavirus May Have Already Infected Half of U.K. Population

Last gasp of the economic profitability of herd immunity??