Post #1305: William and Mary COVID-19 update to 10/22/2021

Six new cases this week, compared to five last week.

Source:  Calculated from William and Mary COVID-19 dashboard accessed 10/23/2021.

As with the national numbers (just-prior post), things seem to have settled into an equilibrium.  No evidence of a coming winter wave of COVID.  No evidence that it’s going away any time soon, either.

Post #1304: COVID-19 trend, last daily post


It has now been almost exactly one month since I had anything noteworthy to say about the U.S. COVID-19 trend.  Rather than continue to repeat the same story (average new case counts are falling, we’re still looking for any sign of a winter wave, vaccinations are flat), I’m going to stop these daily postings on COVID-19 trends.

Maybe I’ll do a weekly update, until such time as there is any material change.

Let me wrap up where things stand in the U.S. as of 10/22/2021.

In a nutshell, the entire U.S. COVID-19 scene is stagnant.  Seems like we’ve reached an equilibrium, for the time being.

Our daily new case rate is stuck at a high level in many northern states.  Nothing devastating, outside of a few excess deaths from lack of hospital capacity in a few areas.  Not going up, but not coming down either.

Our vaccination rate is stuck, with new vaccinations having slowed to a trickle.  People aren’t even getting booster shots very much now, after an initial flurry of interest.

In short, as of now, to me, this looks like the new normal.  Keep your antibodies up-to-date — or not, depending on your tolerance for needless risk — and, barring bad luck, the worst you’ll get will be something like a bad case of the flu.

And what of the one-to-two percent of formally-diagnosed new cases who end up dying, the eight  percent or so who end up hospitalized, and the unknown percent with long-term effects?  You’ll just have to hope that’s somebody else’s problem.

I’ll keep tracking it, and if I see any material change I’ll surely post about it.  But it’s a waste of everybody’s time to keep posting the same story day after day.

Continue reading Post #1304: COVID-19 trend, last daily post

Post #1301: COVID-19 trend to 10/19/2021, no change


The U.S. is now 52% below the 9/1/2021 peak of the Delta wave, with 24.6 new cases per 100K per 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 10/19/2021, from”  The NY Times U.S. tracking page may be found at

The only indication that there might be a generalized winter wave this year is the stubbornly high case rates in a handful of northern states.  If you look at the entire pandemic, Alaska remains far outside the norm, and Montana and Idaho are just starting to appear above the bulk of the states.

In any case, it’s clear that whatever happens this winter is going to be different from what happened last winter.  Below are the first and second years of the pandemic.  I find it tough to visualize the red curve (second year) suddenly retracing the blue curve (first year).

Maybe this all ends with a whimper instead of a bang.  The overall immunity level is high enough to suppress the most rapid spread of disease.  But not enough to take it out of circulation entirely, yet, thanks to the segment of the population that is unvaccinated but hasn’t yet had it.  And between the two of those, we’ll just prolong this pandemic for some time yet.

But, in truth, I have no clue what’s going to happen next.  And my guess is that nobody else really does, either.

Post #1300: COVID-19 trend to 10/18/2021, holiday artifact.


Today we’re looking at the final artifact of the Columbus Day federal holiday.  Cases not reported on the holiday get reported on the next day.  If both of those days fall into the seven-day moving average “window”, that averages out, and we  get the correct new case rate.  But if only one or the other of those days falls into the seven-day “window”, we don’t get a correct estimate of the new case rate..

On the day that the holiday day itself passes into that window, the new case rate dips.  And on the day that it exits the window, the new case rate jumps. Like so: Continue reading Post #1300: COVID-19 trend to 10/18/2021, holiday artifact.

Post #1299: Final COVID-19 update for the week, no change.


New COVID-19 cases continue to fall at a rate of about 12 percent per week.  There’s still no sign of a winter wave.  Alaska remains the only state with more than 100 new cases per 100K population per day, and it seems to be plateauing at that high rate.

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 10/16/2021, from”  The NY Times U.S. tracking page may be found at

Oh, Canada.

No hint of a winter wave in Canada either:

That matters because, in general, the Canadian and U.S. pandemics have been in sync with each other.  And, our winter wave started in and had its worst impact on our cold-climate states.  Together, those factors make Canada something of a canary-in-a-coal mine, vis-a-vis our winter wave.  But so far, there’s no sign of a winter wave there, either.

OTOH, Canada has done a better job of vaccination than we have.

Source:  Government of Canada.

Source:  CDC COVID data tracker, accessed 10-16-2021.

As with the U.S., Canada has not authorized COVID-19 vaccines for children under the age of 12.  So that’s an apples-to-apples comparison on the vaccination rate.  Makes me wonder what it’s like to live in a country where the population is somewhat more rational.  Or, at least, more willing to get vaccinated.

Britain started it.

The United Kingdom started its Delta wave well before the U.S.  And at this point the only thing that we can say for sure is that Britain is proof that vaccination rate isn’t the only factor in play.  They continue to have very high new case rates, despite a higher vaccination rate than the U.S.

They’ve plateaued at just under 40,000 new cases per day for the two-and-a-half months.  The United Kingdom has a population that is almost exactly one-fifth that of the U.S., so that’s the equivalent of 200,000 new cases per day in the U.S.  Or, if you reference the U.S. graph above, they are more-or-less living with a per-capita new case rate equal to the peak of the last U.S. winter wave.

In any case, the longer the U.S. situation situation persists — no sign of a winter wave — the less likely it is that we’ll see a winter wave.

Next, I’m going to re-do my search for counties with no apparent COVID-19 in circulation.  That’s my opening step in asking the question, if this isn’t heading toward a winter wave, where, exactly, is it heading?

Post #1298: William and Mary, five new student COVID cases this week.

Source:  Calculated from William and Mary COVID-19 dashboard.

Is there anything else worth noting?  I don’t think so.

With numbers this low, I’d love to start talking about the potential for false positives.  False positives in the sense of tests results showing the presence of COVID-19 in individuals who never actually had COVID.  If that were common enough, then maybe the trickle of cases currently being observed is actually zero true new cases, and we’re just seeing these results of some small false positive rate.

But I think that’s wishful thinking.  It’s far more likely that , in reality, there is still some low rate of infections circulating among the student body.

Let me work through the arithmetic on that as best I can.

False positive COVID-19 DNA (PCR) tests

It’s tough to talk about false positive DNA (PCR) tests for COVID-19, for several reasons.

First, all the pandemic-denier nuts come out in full force as soon as you raise the topic.  That tends to poison rational discussion when people start claiming that (e.g.) it’s all a hoax, it’s all false testing, and so on.

So I need to start this by averring that I am not a nut.  I’m just trying to run down the numbers.

Second, that aside, it’s difficult to get an estimate of the false-positive rate for DNA (PCR) COVID-19 tests, because, hey, how else can you be sure somebody had COVID-19?  In practice, a positive PRC test is taken as the gold standard for somebody actually having COVID-19.  How can you test the gold standard?

That said, the American College of Pathology (ACP) says that, in practice, COVID-19 DNA (PCR) tests have 98% to 99% “specificity”.  That is, there’s a roughly 1 to 2 percent false positive rate.  (Per this reference).  Other seemingly legitimate studies put the false-positive rate between 0.8% and 4.0% (per this reference, in The Lancet).

I’d call that the same ballpark.  How they know that, I haven’t a clue.  But two seemingly authoritative source more-or-less agree, that’s good enough for me.

Third, there’s a separate confounding issue of PCR tests flagging individuals who actually had COVID-19, have recovered, and yet retain fragments of (dead) viral DNA on and in their nasal membranes.  I have yet to see any quantitative estimate of that, but that is, as I understand it, part of the reason that they don’t want you to get re-tested once you’ve tested positive and have recovered from all symptoms.  Not sure if that’s contained within the false-positive rates cited above, or not.

Fourth, there may be a re-testing protocol for positives.  I don’t think that’s done for COVID-19, but if so — if you double-checked every positive with a second test, and required two positives in a row — that would eliminate false positives due to (e.g.) mishandling of specimens in the lab.  (It would also likely eliminate a lot of true positives, as the DNA test has a pretty substantial false negative rate.)

Finally, and relevant here, the false-positive rate depends on the pre-testing probability that disease is present.  It’s much more of an issue for screening testing — where you test everybody on a population, regardless of symptoms — than testing-for-cause (for those with symptoms or known exposure).

For that last point, I would love to have a single-sentence explanation that anybody could understand, but I don’t.  Will it suffice to say that if somebody has every symptom of COVID-19 and tests positive, there’s little reason to question the validity of the test.  By contrast, an out-of-the-blue positive result, in somebody with no symptoms and no know exposure, should be subject to a higher degree of skepticism.

That pretest-probability effect contributes to the decision not to do screening testing on populations thought to have low probability of infection (such as vaccinated students, in our case).  Aside from the cost of the test, if the actual infection rate is low enough, you reach the point where much of what you are doing is incorrectly forcing healthy people to quarantine, due to false-positive test results.

So, crudely put, false positives are mostly a problem for screening testing, in a population with a low true positive rate.

As I understand it, the only screening testing at William and Mary is weekly testing of the un-vaccinated.  Those now account for just 2% of the student population, or maybe 130 students of the roughly 6600 student residents in and around the Williamsburg campus.

For the vaccinated 98%, testing is only being done for cause.  William and Mary only tests for symptoms or known close contact with an infected individual.  That should be true even for high-risk populations such as student athletes, as the NCAA says that screening testing is not necessary for vaccinated athletes (per the “Resocialization” document on the NCAA website).  The dashboard also includes positives that reported by students who had themselves tested, without having the testing done by William and Mary.

Consistent with that, last week William and Mary performed 162 new tests, but only tested 20 new individuals.  I’m guessing that the bulk of those tests were weekly screenings for the un-vaccinated, and so did not include new (not-previously-tested) students.

If the false-positive rate really is about what the ACP said it was — maybe 1 to 2 percent — then you’d expect maybe a false positive or two per week to arise out of the screening testing.  It’s tough to say.  A lot would depend on the particulars of which test, which lab, which procedures, and so on.  Out of testing-for-cause, I’d guess the expected false positive rate would be a tiny fraction of one test per week.

In other words, no matter how I slice it, using a realistic estimate of the in-the-field false positive rate from a reputable source, I can’t come up with five false positives.

If we knew more we could probably rule it out definitively.  But given the information that is public, my conclusion is that we have to assume that COVID-19 is still, in fact, circulating at low levels within the William and Mary student population.

Post #1297: COVID-19 update to 10/14/2021, no change


New COVID-19 cases continue to fall slowly.  Alaska still has by far the highest new-case rate in the U.S.  We’re seeing high-but-steady rates in the upper Midwest and northern Mountain states.

In short, no change.  Still waiting for the first clear sign of a winter wave of COVID-19.

Continue reading Post #1297: COVID-19 update to 10/14/2021, no change

Post #1286: COVID-19 update to 10/13/2021, no change

The U.S. is now 47% below the 9/1/2021 peak of daily new COVID-19 cases, and new cases continue to decline at a rate of 11% per week.  Today’s count is 27.5 new cases per 100K per day, down from 28 yesterday.

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 10/13/2021, from”  The NY Times U.S. tracking page may be found at

No sign of a winter wave yet.  But today’s weather is newsworthy, and looks like this, per the Washington Post:

Source:  Washington Post

Just to pick a town at random, current conditions in Pocatello, ID, imply 25% indoor relative humidity at 68F/20C, for untreated indoor air.  Looks like conditions similar to that prevail across much of the northern Midwest and Mountain areas.


That’s well into the range that should encourage the spread of viral respiratory infections.  So, if we don’t see a significant uptick in cases within two weeks (typical lag between infection and reporting), I’m willing to call it for no winter wave this year.