Illustrated Recap
Circle A: The late-summer Delta wave largely swept through Southern states. For the U.S. as a whole, the summer Delta wave peaked on 9/1/2021.
Circle B: U.S. average cases have been receding ever since.
Circle C: Until this past week. U.S. daily new case counts stopped falling this past week.
We’re waiting to see if there’s going to be a winter wave. Last year, that started in the upper Midwest and Mountain states, let by the Dakotas. So, naturally, we’re focused on those regions.
Circle D: Until now, the only hint that of anything unusual was that the Mountain and (to a lesser degree) Midwest and Northeast were stuck at their Delta peaks. New case counts fell throughout the South, but generally not in the North.
Circle E: But now, cases are now rising in the Mountain and Midwest areas. But only just.
Circle F: Half the mountain states are now on an upward trajectory. (Graph is on a log scale).
Circle G: And maybe the Midwest reached a shallow inflection point, and is now headed upward. (Graph is on a log scale).
Comparison to last winter
This is clearly not just a repeat of last winter’s wave. At the very least, the winter wave is late this year. Here are the first and second pandemic years on the same graph, each year starting at April 1. The 2021 lines are now in the process of crossing their 2020 counterparts, meaning, any uptick is later than last year.
Maybe this year’s winter wave was confounded by the ebbing of the high rates from the summer Delta wave. Maybe this year will be just-plain different, owing to the high fraction of the population with some immunity. (Though my calculation says no, the greater immunity merely offsets the greater infectiousness of Delta compared to prior variants.)
Maybe the timing of this year’s winter wave was slowed by the generally warmer and wetter fall in the U.S. Midwest and Mountain states for 2021, compared to 2020.
Here’s 2020, generally cool (left) and dry (right) in the middle of the U.S.
Here’s 2021, generally warm (left) and somewhat wetter (right) in the middle of the U.S.
Summary
This week’s interesting development is that daily new COVID-19 case counts stopped falling, for the U.S. as a whole. As was true last year, that seems to be starting with the Midwest and Mountain states. It’s still not clear that we’ll have a winter wave, but these seem to be the first hints of it.
