Post #1325: COVID-19 winter wave, Mountain states

Posted on November 18, 2021

Map courtesy of

Data source for this and other graphs of new case counts:  Calculated from The New York Times. (2021). Coronavirus (Covid-19) Data in the United States. Retrieved 11/18/2021, from”  The NY Times U.S. tracking page may be found at

The U.S. winter wave continues apace, except in the Mountain region.  As you can see, the northernmost mountain states now form sort of a “hole” in the northern tier of U.S. non-Pacific-coast states.


Last year’s winter wave was led by the Midwest and Mountain regions, both of which peaked sometime around Thanksgiving.  This year, by contrast, while the Midwest is now rising rapidly, the Mountain region seems to have stalled (circled above).

Within the Mountain region, instead of any uniform trend, it’s a mixed bag.  As shown below, three states appear to have peaked.  Those are the same states that are circled on the first map graph above.

The three northernmost Mountain states are now showing a downward trend.  Based on my counts, it doesn’t look like they’ve hit herd immunity.  So what’s going on?

Turns out, it looks like they’ve had their winter wave.  Tough to say why, exactly, but it looks like the end of their summer Delta wave simply ran into and effectively became their winter wave.  Note that there’s no end of the Delta wave for those states.  Cases continued to climb from July all the way through to early October.  And has been noted in earlier posts, Idaho already had to declare “crisis standards of care”, allowing physicians to ration hospital beds to those who seemed most likely to survive.

The upshot is that instead of a distinct winter wave with a sharp peak late in November, their summer Delta wave just continued, with the result of a broad peak spanning most of September and October.  If I had to guess, I’d guess they’re done for the year.

The rest of the Mountain states, by contrast, had a low peak in early September, consistent with the end of the summer Delta wave.  And they’ve (mostly) started on a new Winter wave.  Those states don’t appear to be done yet, for 2021.

Time and again, the pandemic has run right up to the point where hospitals are full, and then stopped.  It’s as if there’s only a finite subset of the population at risk of infection at any one time.  And once they’ve been infected, the pandemic runs out of steam for a while.

And so, in those three northernmost Mountain states, it surely looks as if the summer Delta wave worked its way through all the infection-eligible population.   For all intents and purposes, it looks like the pandemic has simply run out of steam, in those three states, for now.  And so, there won’t be a  winter wave cresting around Thanksgiving.  Instead, they had two months of high case loads under Delta, leading to (among other things) crisis standards of hospital care in Idaho.

Maybe that bodes well for the entire U.S.  Maybe we’re finally reaching the point where there’s just some modest subset of the population left to be infected.  And so instead of a rip-roaring winter wave, as we had last year, maybe we’ll all go the way of WY, MT, and ID.  Maybe the people still capable of being infected will end up so thin on the ground that we’ll have just a modest peak this winter.