Post #1079: The U.S. COVID-19 fourth wave has started, I guess.

Posted on March 27, 2021


The current COVID-19 story is that we have new, more-infectious variants of COVID-19 here in the U.S.  And so, in theory, we’re in a race between the spread of those more infectious variants, on the one hand, and vaccination, on the other.

Over the past few weeks I’ve been tracking the COVID-19 new case data, waiting for new-case rates in a handful of states to turn upward.  These are states that, based on CDC or other data, were reported to have a high fraction of at least one of those new variants.

And now, those new-case rates have turned upward.  Mostly.  And, yeah, rates appear to be turning upward at more-or-less the time you would expect, based on prevalence of the new variants.  (When about half of cases are the new variants.)

But new case rates have also turned up in a lot of states where the presumed prevalence of those new variants is far less.  At more-or-less the same time as the high-variant states.  And at more-or-less the same rate as those states.

You may find other people who are just rock-solid sure that they are looking at the impact of these new COVID-19 variants.  But I’m not so sure what I’m looking at.

Regardless of the reason, the data are what they are.  New case rates are rising.

National trend

Nationally, in three graphs:  1) We’re now back to 24% of the peak level, 2) the overall US trend is up, and 3) cases rose yesterday in the overwhelming majority of states.

Pace of vaccination and limits of vaccine acceptance.

That said, the pace of vaccination is picking up, and we have not yet reached the limits of vaccine acceptance in the elderly.  Here are my most recent snapshots of the CDC COVID data tracker, showing fraction of the elderly vaccinated.  That’s a rate of 0.5 percentage points per day, so this has not yet stalled out.

In Virginia, snapshots from 3/27/2021 (top) and 3/22/2021 (bottom) show about 0.4 percentage points per day, or roughly the same pace as the U.S. data.

The upshot of all of that is that vaccination of the elderly continues apace, and, contrary to what I guessed would happen, we have not yet hit the limit of vaccine acceptance in the elderly.

If I now update my “herd immunity” chart based on the recent record of more than 3M vaccine shots per day, then here’s where we stand, and where we would be projected to stand as of April 1 2021.

(I should say that this chart continues to assume that once you’ve had COVID-19, you are fully immune.  There’s now a pretty good body of evidence to say that some modest fraction of that population is subject to re-infection.  But my impression is that re-infections are not nearly as dangerous, on average, as the initial infection.  So, for consistency, I’m sticking with the (incorrect) assumption of 100% immunity of the already-infected population.)

Here’s the same chart, the last time I recalculated it, less than two weeks ago.

So, we are making slow progress.

State-level detail.

If you look at the state-level detail, it’s not crystal clear that this is being driven (or, driven only) by the more-infectious variants.  New case rates are turning upward all over, not just in the states presumed to have a high fraction of these new variants.

As you can see below, the majority of states are trending upwards now in the Northeast, South Atlantic, and Midwest regions.  The South Central, Mountain, and Pacific regions are more mixed.

And that’s what has me a little uncertain as to what’s going on.  Everybody noted that Florida had a high incidence of these new variants.  But nobody said that about (e.g.) West Virginia, New Hampshire, Vermont, or North Dakota.  But new case rates are rising as fast there as they are in (say) New York State.

So whatever is driving this, it doesn’t seem to be quite as simple as “new COVID-19 variants”.  Either that, or the distribution of those new variants managed to even itself out across all those states, in just a few weeks.