There's a lot of confusion on this. It all comes down to how you define "herd immunity".
1) Traditional herd immunity: enough people get it that the virus dies on its own w/o any special measures - 60-70% for covid, maybe more with overshoot. This value is endemic to the virus and the local population behavior and density. It assumes normal behavior.
2) Whatever you call what we're doing now ("effective herd immunity"?) where roughly 60% stay mostly isolated out of the "herd": cases drop, maybe we wait it out until a vaccine. This number is very malleable based on behavior.
The problem with 2 obviously is the virus never really goes away, people get complacent, then we get this slow burn back to traditional herd immunity.
So I don't think you ever get to virus
over w/o a vaccine or traditional herd immunity. But it does explain this phenomenon where cases seem to start dropping once you hit 20-30% of the population infected. There just aren't that many more people in the pool who could potentially get it.
Hence my concern about schools opening up a new segment (parents, teachers, teenagers) to the pool that currently is mostly out of the pool (not all parents, but a good chunk of them). I know plenty of parents who are taking the virus very seriously and really don't want to send their kids back to in-person classes, but they're still having a really tough decision about what to do right now in places where schools are giving the either/or option.
https://www.theatlantic.com/health/a...avirus/614035/