I am not sure how mysterious this is. As Scott Gottlieb (hardly a COVID denialist) pointed out[1], we are getting the impacts of some level of immunity in populations.
Herd immunity itself is a threshold, but it isn't a binary state. As you near it, the "susceptible" pool becomes fewer and fewer. Since reinfections appear rare (though not impossible) and immunity seems robust and at least 6-12 months long, it is no mystery that cases will begin to fall.
There is also the established pattern of coronavirus infections. In the northern hemisphere infections are at their worst from mid December to mid January. Near the equator the established pattern is a kind of double hump in the summer that peaks and fades around September which is what people saw. It is quite possible that at a macro level these patterns were repeated and attempts by people to contain the virus were of limited utility.
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[ 3.4 ms ] story [ 14.7 ms ] threadHerd immunity itself is a threshold, but it isn't a binary state. As you near it, the "susceptible" pool becomes fewer and fewer. Since reinfections appear rare (though not impossible) and immunity seems robust and at least 6-12 months long, it is no mystery that cases will begin to fall.
[1] https://twitter.com/CNBCClosingBell/status/13578120997836431...