Post #1239: COVID-19 trend, a sharp drop in new cases.

Posted on September 9, 2021

The U.S. stands at 46 new COVID-19 cases per 100,000, down about 11% from one week ago.  It increasingly appears that the peak of the Delta wave was 9/1/2021.

There are a few caveats.   Some of the recent sharp decline in new cases may be the temporary impact of the Labor Day holiday.  And if that was the peak, then the U.S. experience no longer matches that of Great Britain.  Nor has Canada peaked, and we’re usually pretty well in sync with Canada.

Those caveats aside, on the face of it, it looks like the U.S. Delta wave has peaked.

The decline looks far more dramatic when I plot it in natural units instead of logs, as above.  The graph below also makes it appear that this current decline is appears far sharper than the decline following Memorial Day.  That suggests that the normal post-holiday drop in new cases cannot fully account for the current decline.

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 9/9/2021, from”  The NY Times U.S. tracking page may be found at

Another factor suggesting that this decline is real is that California and Florida account for a large part of it.  (The impact of California accounts for the large negative growth rate in the Pacific region, first graph above.)  Both states peaked prior to Labor Day.  Neither state mentions any data reporting issues.  (I.e., the California state website shows the same sharp decline in California that I do).

Finally, while this last little bend in the curve has been quite sharp, the end of the line is about where it ought to be.  The actual case counts (red) sit right on top of the month-old “by-eye” projection of where this wave appeared headed.

So a peak isn’t a surprise.  And maybe I should not look a gift horse in the mouth.

In summary, after crudely smoothing out the data reporting anomaly from two days back, and doing nothing else, the resulting graph now suggests that we’re past the peak of the Delta wave.

This is a temporary reprieve, for sure.  There’s a pretty strong consensus that we should expect to have a significant U.S. winter wave of COVID-19.  But we’ll take what we can get.

I should check in with Canada and Great Britain.  No peaks there, so that’s a caveat.  Right now, this is a uniquely American phenomenon.

As an afterthought, I’ll have to do that same crude smoothing trick next Tuesday, as the non-reporting from Labor Day passes outside of the seven-day-moving average window.  But until then, all I have to do is plot the data and see whether it continues to drop.  Sure beats watching it rise.