Thread by @AndrewNoymer

HERD IMMUNITY, a short thread.

Already much has been said about the so-called "herd immunity strategy". That it's better to get it all over-with as soon as possible — viz., without social distancing. This was more/less the UK gov't approach for a time, altho they have changed...

... But it's important to recognize an important aspect:

While not all plans are "'THE' herd-immunity strategy" (i.e., "damn the torpedoes, full speed ahead!")...

ALL strategies *are* herd immunity approaches one way or another. ...

The core logic of #FlattenTheCurve is to lengthen the period over which everyone gets exposed, and, putatively, immune. Durable immunity cannot be taken for granted but it's a good working assumption at this point.

...

The end point of the steep curve or the flat curve is the same: herd immunity.

Absent a vaccine, virus will keep spreading until the herd immunity threshold is achieved. USA-style "lockdowns" are not absolute, so the best we can do is flatten the curve (and we *still* *can*!).

So, don't confuse "the herd immunity strategy" with "herd immunity," writ large. The former was a dunderheaded idea; the latter is an aspect of the outbreak that all successful strategies will exploit to our advantage. ...

A corollary is that as we (eventually) ease social distancing, a second wave is virtually inevitable, if we are, at that time, far away from the herd immunity threshold.

The "lockdowns" lower R0 and Rt. These quantities are not cast in steel. They can go back up, and will...

... if we prematurely end "lockdown".

When we can do so safely will depend on the data/situation.

An early estimate of mine was, not before 1 June 2020, and that still seems about right. We'll know more as we push along. @ScottGottliebMD has some recent informed tweets on this.

In summary:

— We want herd immunity.

— Just not too soon.

— The so-called "herd-immunity strategy" is not prudent.

— But the concept of herd immunity remains crucial.