This article has an interesting take on what "herd immunity" actually means with covid.
https://www.theatlantic.com/health/a...avirus/614035/
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But she declines to endorse any particular numeric threshold for herd immunity. She’s not comfortable with the idea of a single number at all. What’s important to her, rather, is that people are not misled by the idea of herd immunity. In the context of vaccination, herd-immunity thresholds are relatively fixed and predictable. In the context of an ongoing pandemic, thinking of this threshold as some static concept can be dangerously misleading.
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“COVID-19 is the first disease in modern times where the whole world has changed their behavior and disease spread has been reduced,” Britton noted. That made old models and numbers obsolete. Social distancing and other reactive measures changed the R0 value, and they will continue to do so. The virus has certain immutable properties, but there is nothing immutable about how many infections it causes in the real world.
What we seem to need is a better understanding of herd immunity in this novel context. The threshold can change based on how a virus spreads. The spread keeps on changing based on how we react to it at every stage, and the effects compound. Small preventive measures have big downstream effects. In other words, the herd in question determines its immunity. There is no mystery in how to drop the R0 to below 1 and reach an effective herd immunity: masks, social distancing, hand-washing, and everything everyone is tired of hearing about. It is already being done.
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Basically while covid
innate herd immunity may be something like 60-70%,
effective herd immunity could be as low as 20% - assuming all the office drones like me keeping working from home and being careful.
However it seems to be the case that as soon as cases let up, people let their guard down, and the virus plows into a new fresh field of uninfected people. Schools re-opening could be that field.