Post #1335: COVID-19 trend to 12/1/2021

Posted on December 2, 2021

I’m just marking time in this post.  The situation isn’t greatly different from the way things stood yesterday.  It still doesn’t look like we’re going to have much of a winter wave, for the U.S. as a whole.

Arguably the most interesting thing happening right now is the lack of new cases in ID, MT, WY. 

The U.S.

Below you see the first and second years of the pandemic, for the U.S. as a whole.  The top graph is for the entire year starting April 1 of each year.  The second graph is just winter wave in isolation — the period just prior to Thanksgiving to just past New Year’s Day.

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 12/22021, from”  The NY Times U.S. tracking page may be found at

As you can see from either graph, we have just about half as many daily new cases as we did at this time last year. 

And, unlike last year, new cases actually peaked and plateaued well before Thanksgiving.  Last year, new case counts were rising right up to Thanksgiving day.   This year, the actual peak was a week before Thanksgiving (11/18/2021), followed by a week of flat new case counts.

The curious case of the dog that did not bark in the night.

Here are maps of daily new COVID-19 case rates from 12/1/2020 and 12/1/2021.

Maps courtesy of

When I put those to maps into an animated .gif, I'm not entirely sure what to make of it.  By eye, I need to add Nevada to the cluster of Mountain states that were in the thick of the winter wave last year, but not this year.  And it's very clear that the deep South has next-to-no activity this year, compared to last year at this time.

Meanwhile, New Hampshire and Vermont stand out in the Northeast.  I'm tempted to say that this is a contrast of the cold-climate states with low and high historical rates of infection.  For example, ID,MT, WY all have more than 18% of the population with some reported infection so far.  By contrast, only 8% of the population of Vermont has been infected.

(That may not seem like much, but recall that there are about two true infections for every reported infection, based on CDC seroprevalence (blood antibody test) surveys.  That 10-percentage-point gap in reported infections could, in theory, represent a nearly twenty-percentage-point difference in true cumulative infection rates between those two areas.)

That analysis is a bit too casual.  I wouldn't take away any hard conclusions from it.  That said, to some degree, there does seem to be a contrast now between the states that are most improved and least improved, relative to their situation last year.  And that contrast seems to be highlighting those who have already incurred high infection rates versus those who have not.  I guess I'll try to formalize that in my next analysis.

Edit:  Nope, there's nothing to that hypothesis that the current high-case-rate states are now "paying for" their prior low infection rates.  If I do my "formal" calculation of the amount of immunity in a state (weighted average of prior infections plus vaccinations, less assumed overlap), there's no systematic relationship between the level of immunity and the difference between the 2020 and 2021 winter waves.  The dominant factor driving state-level differences in immunity is the vaccination rate.  Because of that (e.g.) Vermont and New Hampshire should both have higher levels of population immunity than any of ID, MT, WY.