Post #1109: COVID-19 trends through 4/15/2021

Posted on April 16, 2021


Michigan gets a little bit more of a break, and certainly looks like it has passed an inflection point.  I.e., the graph is now starting to look like the top of a hill.  So maybe they are at or nearing their peak of daily new COVID-19 cases.

Source for this and other graphs:  Calculated from The New York Times. (2021). Coronavirus (Covid-19) Data in the United States. Retrieved 4/16/2021, from”  The NY Times U.S. tracking page may be found at

The U.S. as a whole is just drifting along.  No strong trend, but no end in sight either.

If the U.S. is going to take a beating from the U.K. variant, somebody needs to tell Florida and Texas to get with the program.  Because that’s clearly not happening there despite the U.K. variant now accounting for the overwhelming majority of new cases in those states.

In that same vein, an odd thing seems to be happening with the Helix Corporation data showing the fraction of new cases attributable to the U.K. variant.  The U.K.-as-fraction-of-all-cases number appears to have passed an inflection point and is now rising more slowly.

Maybe “odd” is the wrong word there.  That’s what’s supposed to happen — the growth of this variant follows an S-shaped (“sigmoid”) curve.  But it’s a good sign, nevertheless.  It pretty strongly suggests that if there’s hasn’t been an explosion of new cases in FL and TX so far, there probably isn’t going to be.

This is the U.S. fraction of cases through April 12, from the Helix Corporation. The graphs for the individual states show the same sigmoid shape.

Data sourced from the Helix® COVID-19 Surveillance Dashboard. Accessed at on 4/16/2021.

The elderly are still getting vaccinated. We now have 80% of the elderly vaccinated, and just shy of half of the entire U.S. adult population vaccinated.  You really have to start wondering what it’s going to take for this “herd immunity” thing to kick in.   But, as I laid out in some prior posts, there are good reasons that the raw percent vaccinated overstates the impact of the vaccine on stopping the pandemic.  By-and-large, the first doses of the vaccine have gone to the parts of the population that are least responsible for the ongoing spread of COVID-19.

This is yesterday’s data, but I don’t feel like waiting for CDC to post today’s data.


Contrast the U.S. third and fourth waves.

We’re now more than three weeks into the U.S. fourth wave.  I’d like to go back and compare the start of the U.S. fourth wave with the start of the U.S. third wave.  Like so:


The U.S. trend right now looks similar to the U.S. trend at the start of the U.S. third wave of COVID-19.  In both cases, at three weeks, In both cases, daily new cases had risen something in excess of 25 percent above the previous minimum.

But the regional trends are qualitatively different.  In the U.S. third wave, by the end of the third week, almost all regions were showing an upward trend in daily new cases, and some acceleration in that trend.  Now, by contrast, there’s nothing like that sort of nation-wide uniformity.  Two regions (Northeast and South Central) have declining trends.  Even the trend in the Midwest, which  has led the fourth wave (via MI and MN), shows signs of flattening out.

Make of it what you will, but to me, the situations as of the third week appear quite different.  At that point, the U.S. third wave — what I call the coronavirus season wave — appeared to be gathering steam across the U.S.  But now, you really can’t say that.  Now you have a handful of states with a strong upward trend, and a lot of states that are just drifting along.  By eye, at least, it just doesn’t look like we’re getting ready for anything even remotely resembling a repeat of the U.S. third wave.