Post #1185: Getting oriented for the COVID-19 Delta wave

Posted on July 25, 2021

Panic early and often

The next opportunity to check the trend in new U.S. COVID-19 cases will be Tuesday.  That’s because the great majority of states have stopped reporting that information on weekends.

In the meantime, this post is my way of stepping back and getting oriented for what I think is coming next.   And to ask myself if there’s anything I need to do to get ready for it.

I find that if I don’t write it down, it’s all too easy just to fuzzy-think my way along.  Something along the lines of “ah, you know, maybe things won’t be so bad”.  Putting this down in black-and-white, in public, is my way of forcing myself to be as realistic and accurate as I can manage.

A further purpose is to get ready for the apocalyptic popular press reporting that is almost certain to occur if this wave unfolds as I expect.  It’s a lot easier to shrug that off if you are ready for it, and predicted it, rather than get caught up in the moment.

Here’s the outline of what I intend to do.

Part 1:  An expected timeline, and what that implies.

The first thing I need to do is be explicit about how I think the Delta wave will unfold.  It’s not sufficient just to keep saying that things will get bad.  How bad, how fast?

1.1  Expected timeline for the U.S. fifth wave of COVID-19, given the information currently available. I believe we’ll see daily new case counts that exceed those of the U.S. third (winter) wave.  But where the third wave built up over months, this one is going to be short and sharp.

1.2 Impact on college and other school fall semesters.  Given my estimated timeline, don’t be surprised if colleges and possibly other schools postpone the start of Fall semester, or at least the start of in-person classes.   Looks to me like the start of fall semester for many places will more-or-less coincide with the peak of the Delta wave.

1.3 Are there any other predictable disruptions, based on what happened in prior U.S. COVID-19 waves?


1.1:  Expected timeline, or it’s tough to make predictions, especially about the future.

In this section I make the case for the U.S. Delta wave to last seven weeks, and for it to maintain more-or-less the current rate of growth for that entire period.  That will put the peak of the Delta wave around 8/17/2021, with around 80 new cases / 100,000 / day as the peak rate of daily new COVID-19 cases.

In other words, I expect the peak of the U.S. fifth (Delta) wave to be slightly worse than the peak of the third (winter) wave, and I expect that to occur just a bit over three weeks from today.

I hope it goes without saying that this entails a lot of guesswork and some crude reasoning-by-analogy.  That said, this is my best guess as of today.

If the facts change, I’ll change my mind.

The projection is based on:

  • The relatively smooth (constant-growth-rate) trajectory of prior waves, andreasonably uniform length of each wave across states.
  • The apparent peaking of the Delta wave in Missouri seven weeks after the start of the wave there, with no obvious efforts by Missourians to stop it.
  • An estimate of 6/29/2021 as the start date of the U.S. Delta wave — the date on which U.S. new case counts really began to take off.

The rest of this section lays out the details.


The first thing I want to do is dredge up some graphs that I’ve shown recently, just to make a point about how regular the past COVID-19 waves have been.  Be warned that a good bit of this next part is purely my impression of how this works, having spent the last year and a half studying the numbers.

The first rule is that  once a wave gets going, it tends to proceed at a fairly constant rate, until it peaks.  Take a look at the up-slopes of the five prior COVID-19 waves.  In general, what you see is a smooth line at a roughly constant rate of growth, except for data-reporting artifacts arising from holidays.  You don’t see (e.g.) a bunch of plateaus, or widely-varying rates of growth on any one upslope.



In fact, once you start scrutinizing the dips, you find that virtually all the significant dips in the curve are, in fact, artifacts of holidays.  Absent that, the general rule is that once a wave gets start, at a given slope (rate of growth), it continues at that rate until it peaks.

The second rule is that the waves tend to have the same length across regions or states, even if they start at different times.  Below, the blue line is the U.S., the first graph shows the Midwest leading the country on the winter wave.  The second graph shows the

Third, its starting to look like Missouri — the first state for this wave — is now beginning to top out.  And so, I’m going to rely on Missouri for my best guess for how long this wave will last.  There, they appear to be topping out seven weeks after case counts began rising.

As far as I can tell, there’s no obvious reason for Missouri to be peaking now.  It doesn’t appear that residents of that state did much of anything in response to this most recent COVID-19 outbreak.  Here are some charts from Carnegie-Mellon University COVIDcast, and one from CDC data showing the actual fraction of the population vaccinated.

Near as I can tell, a few percent of the population decided to wear a mask, and a few percent decided to skip restaurant meals for the time being.  Otherwise, in terms of actually vaccinations, vaccine acceptance (saying that you’d accept a vaccine if offered), bar visits, and so on — pretty much no change at all.

I’d say the behavior of the population more-or-less mirrors that of the Missouri government.  Not only are there (e.g.) no mask mandates statewide, but the state is suing St. Louis County for imposing one locally.  The state is actively suppressing local decisions to try to get people masked up again.

Finally, right now their daily new case rate is less than half their wintertime peak.  And deaths are only now starting to creep up.  They are average just 11 per day currently.  So, I guess, other than a few areas where the hospitals are full, they really don’t see much need to take any action.

Source:  CDC COVID data tracker, downloaded 7/25/2021

It’s not clear that Missouri is an ideal model for the rest of the states because they really haven’t hit hospital capacity yet in most of that state.  And, accordingly, they really haven’t done anything about this current (Delta) wave.

To the extent that other states will hit that hospital capacity constraint earlier, or are less hide-bound about mask mandates and vaccines, you’d expect to see actions taken to reduce the spread of COVID-19 during this fifth (Delta) wave.  So even if this wave just goes away, by itself, in Missouri after seven weeks, it’s not clear that it ought to last seven weeks everywhere.

That said, this is my best guess for the pattern that most states will follow.  Cases will grow unconstrained, and there will be no material actions take to address this latest outbreak.

1.2 Impact on college and other school fall semesters.

Let me assume that this wave tails of just as rapidly as the winter 2020 wave did.  On average, daily new cases fell by about 20% per week as the winter wave receded.  At that pace, the full picture starts to look like this:

Now let me look at that in light of two school calendars that are relevant to me:  The College of William and Mary, and Fairfax County Public Schools (FCPS).

William and Mary starts freshman orientation on 8/27/2021, and the first day of classes is 9/1/2021.  FCPS plans to begin school on 8/23/2021.

Based on my projection, that will be past the U.S. peak.  But, needless to say, all of those dates will fall well within the period during which U.S. new COVID-19 cases will be at fairly alarming levels.  At least, in so far as people were alarmed at the rates during the wintertime peak.

At the very least, my projection for the situation for start-of-school 2021 (9/1/2021) is vastly different from the way things looked last year (9/1/2020).  The only thing that will look better this year, compared to last year, is that everybody age 12 and up who wanted to get vaccinated has done so.

Plausibly, given that you can’t turn on a dime, even if I’m precisely correct about the timing of the peak, those institutions will have to make the go/no-go decision while U.S. cases are still rising at (what I could classify as) an alarming rate.

Obviously, I can’t read the minds of the decisionmakers.  But, at the minimum, I’d be surprised if William and Mary opened with full in-person classroom attendance on 9/1/2021.  Vaccines or no vaccines.  For elementary and high schools, I’m  not even going to hazard a guess.  All I can say is, if the current trend continues, that open-or-not decision is going to be difficult.

1.3 Are there any other predictable disruptions?

Additional restrictions on public gatherings:  Bars, restaurants, church services, gyms, and the like.

This is total guesswork, but I’m betting that this is going to come on so fast, nobody will get the decisions made in time to shut down or restrict any of these venues.  Certainly, some states appear to have taken a position that no such restrictions will ever be reimposed.  But even in states where such restrictions might still be on the table, they’ll have to act fast if they are going to do any good.

Best guess:  Not gonna happen.  Certainly not in states with Republican governors.  Maybe nowhere.

Hospitals:  I believe that the average COVID-19 hospitalization now lasts about 12 days, and that about 8.5% of persons diagnosed with COVID-19 will be hospitalized.  If I then “integrate” over the daily new cases data, using those rates, I get this estimate of the number of persons who will be in the hospital, at any one time.  (This is not daily new hospitalizations, it’s the number of persons in the hospital, regardless of admission date).

Just as a reality check, CDC says that there are about 24,000 COVID-19 patients in the hospital as of 7/21/2021 (per this reference), or about 25% less than what my calculation gives.  So I’m in the ballpark.

The same CDC reference shows the wintertime peak in hospitalized COVID-19 patients as just over 125,000.  By contrast, my calculation, even adjusting downward by my apparent overshoot, gives about 190,000 at the peak.

That said, it’s probably true that as hospitals filled up, physicians raised the bar for hospitalization.

Best guess:  U.S. hospital capacity will be (at least) as strained at the peak of the Delta wave as it was at the peak of the U.S. wintertime wave.  We will once again be seeing stories of many areas running out of ICU beds.

Consumer supply chain issues:  I’m betting that there are none.  That’s based on a combination of how quickly this will peak, and my vague understanding that a lot of the “critical” industries have more-or-less required vaccination as a condition of employment.

The U.S. population as a whole may not have learned its lesson.  Nor does it look like most state or Federal public health agencies have.  But when it comes to big for-profit enterprises, the first rule of staying in business is to avoid risks that can be avoided.  Maybe this is my economist’s bias, but if anything continues to function right in the next three weeks, I’d bet on those critical businesses