Post #1028: Trends to 2/24/2021

Posted on February 25, 2021

The decline in new cases that begin around 1/8/2021 seems to be flattening out.

Source:  Calculated from NY Times Github COVID-19 data repository, data reported through 2/24/2021.

That’s now clearly a broadly-based change.  Every region other than the Pacific region is showing it (red circles above).  The Pacific region is the exception because new cases continue to fall in California.  The return to normal reporting in Texas (gray line, South Central region) results in a little exaggeration of this change.  But only a little.

Finally, three views above show you how broadly-based this is.  The two charts of all states now clearly show the lines flattening out, at the right-hand edge.  And in the course of a week, we went from consistently having >40 states show a day-to-day decline in new cases, to roughly a 50/50 split between states showing decline versus stated showing an increase, in any given day.

The only other thing to note is that lack of consistency from day to day.  About half of states show declines on any given day.  But which states those are appears mostly random.  Basically, we’re now looking at day-to-day “noise” variation in the numbers in that last chart.

At this point, my best guess for this remains “the end of coronavirus season”.  Which is to say, no explanation at all.  It’s just that whatever drove the rates up with the onset of cold weather last year has now run its course.

There’s no strong evidence for that, but I will point to two facts.  This change in trend appeared first among the “bellwether” states that led the upward portion of the U.S. third wave (Post #1018).  Those were maybe a week or more ahead of the rest of the U.S. in flattening out their downward trends.

Source: Global Seasonality of Human Coronaviruses: A Systematic Review Sangshin Park,Yeonjin Lee,Ian C Michelow,Young June Choe Open Forum Infectious Diseases, Volume 7, Issue 11, November 2020, ofaa443, Published: 18 October 2020

The other is how long “coronavirus season” lasts for other human coronaviruses, on average.  And here I’ll return to a graphic that I’ve used before.  I read the graph above as saying that you should expect, at most, three months of really high infection rates.  Typically.

And if you step back and look at the entire pandemic, this third wave went from roughly mid-October to mid-January.  Or three months.  So if COVID-19 behaves like the typical coronavirus, we’re about due for this wave to be over.

So, maybe for the next few weeks, the U.S. will just ease along toward some baseline level of virus circulation.  Until such time as the U.K. strain, or some other factor, pushes rates up again.