* The WHO updated their guidelines for PCR tests in a way that could cause this (because the tests were being misused, the new guidelines clarify how they're supposed to be used in a way the previous ones did not), except the update also happened after the drop started.
* The drop is worldwide, it seems like only a handful of countries aren't experiencing it. In most places it started at various parts of January, but here in Illinois it started in November (minus spikes that correlate to Thanksgiving/Christmas/New Years).
* There is no correlation in the US between "lockdown states" and "reopened states". It's just dropping everywhere.
My personal belief: We already hit herd immunity in most of the world a month ago. There's a few possibilities for why this would be (underestimating cross-immunity or how far the virus has spread, for example), but it's really hard to say for sure.
* The WHO updated their guidelines for PCR tests in a way that could cause this (because the tests were being misused, the new guidelines clarify how they're supposed to be used in a way the previous ones did not), except the update also happened after the drop started.
* The drop is worldwide, it seems like only a handful of countries aren't experiencing it. In most places it started at various parts of January, but here in Illinois it started in November (minus spikes that correlate to Thanksgiving/Christmas/New Years).
* There is no correlation in the US between "lockdown states" and "reopened states". It's just dropping everywhere.
My personal belief: We already hit herd immunity in most of the world a month ago. There's a few possibilities for why this would be (underestimating cross-immunity or how far the virus has spread, for example), but it's really hard to say for sure.