As the epidemic progresses the pool of easily-infected individuals dries up and the virus has to search out new victims who are less-easily infected.[from OP link]
__________
That has Bingo written all over it.
Delete the assumption that everyone who is exposed to COVID gets COVID. Couple it with the apparent fact that a significant number of infections result in mild and even no discernible symptoms.
Yes, herd immunity could easily lurk in the 20-30% range.
Last number I heard is that this bug will get to 82% if there is no vaccine, that absent a vaccine all we can do is flatten the curve, hope for treatments, and hope that this bug mutates into something less deadly....as Bret Weinstein has been saying from the Jump is highly likely.

