Post #1237: The COVID-19 situation at William and Mary

Posted on September 8, 2021

I’m writing this post to provide a little perspective on the COVID-19 situation at William and Mary.  Yesterday they updated their dashboard to reveal that there have been 115 known cases on campus.

To reiterate what the William and Mary administration said about that, almost all the cases are mild or asymptomatic breakthrough infections.  (That they are almost all breakthrough is unsurprising, given that 93 percent of students report that they have been vaccinated.)

My main takeaways are that:

  • Many Virginia universities and colleges are having a problem with COVID-19 in the 2021 fall semester.
  • The rate of new cases showing up in Virginia universities seems roughly similar to the Virginia 18-24 population as a whole.
  • William and Mary appears to have a much-worse-than-average problem this semester, based on a comparison to four other Virginia universities and to the current rate among all Virginia residents age 18 to 24.

How does William and Mary compare to other Virginia universities? 

In a situation like this, it’s sometimes helpful to look around at the rest of the state (as in Post #788, last year).  Below I’ve quickly tabulated the numbers for a handful of Virginia universities.

This is a rough cut, in that some of these combine students and faculty, and some of the enrollments my overstate the actual residential enrollment to which the testing applies.  There’s nothing systematic about which universities I chose.  They were just the first ones to come to mind in this context.

The other unknown is the effective start date of the school year.  The longer they’ve been back on campus, presumably the more time they’ve had to identify infected students.  Radford, for example, began classes on 8/23/2021.  U Va started on 8/24/2021.  W&M began classes on 8/19/2021. 9/1/2021.  (I looked at the wrong calendar).  So W&M has had fewer person-days on campus in which to find infected individuals (or to have cases develop).

That said, at first blush, none of the numbers for William and Mary look good.  Every Virginia university is having some sort of a problem, but ours looks somewhat worse than the comparison group. A combination of fewer tests and more cases particularly stands out.

For the high level of active cases, that must be due to the fact that these are almost all newly-reported tests.  Which is consistent with the late date for start-of-classes.  By definition, I think cases are considered active for 14 days following positive diagnosis, unless symptoms persist beyond that point.  In other words, if almost all of those tests took place less than 14 days ago, then by definition, almost all of the cases will be considered “active”.

Not shown — and to me, by far the oddest aspect of the W&M counts — is that W&M found more than 100 cases by testing fewer than 400 people. It’s on-order-of a one-third positivity rate (infections to persons tested).

I can’t quite grasp how they could have done that.  I surely hope that’s due to testing symptomatic persons only, then following up with contact tracing.  That “target rich” testing pool could plausibly yield such a high positivity rate.  To be crystal clear, it’s not even remotely plausible that the high positivity rate shown reflects a cross-section of the campus population.

In any case, the main takeaway is that everybody is having a problem with COVID-19 in the Fall 2010 semester.  (I was going to say more of a problem than last year, but Radford had a terrible time last year.  Now they have just about the best numbers on the table.)

The plain reading of the numbers makes it look like more of a problem at William and Mary than elsewhere.  But the oddity of the testing numbers (100 positives out of 400 persons) means that William and Mary’s testing has been driven by symptomatic cases (and possibly contact tracing).  But everybody tests symptomatic individuals, so that, by itself, would not explain the higher numbers at William and Mary compared to Virginia peers.


What are the rates of new COVID-19 cases in the college-age population of Virginia?

Data source for this graph of new case counts:  Calculated from The New York Times. (2021). Coronavirus (Covid-19) Data in the United States. Retrieved 9/4/2021, from”  The NY Times U.S. tracking page may be found at

It’s no secret that the overall rate of new cases is higher now than it was last fall. Above, you see the rate of new cases per 100,000 population per day for Virginia, in the first year of the pandemic and the second year of the pandemic.

It’s tough to compare the COVID-19 rates on these campuses to the COVID-19 infection rate in the community.  The problem is that we’re seeing cumulatives of all cases over some period of time, for the college data.  For the community, we’re seeing daily cases.

In short, I have to guess the number of days of exposure that have occurred so far, at these college campuses.  For example, I’d have to use a longer period to make the comparison to the colleges with early start dates, and a shorter period for comparison to colleges with more recent start dates.  Based on class start date for William and Mary (and arrival on campus prior to start of classes), I’m just going to use nice, round three and two week periods.  So for this next bit, I’m combining Census data showing 802,000 Virginia residents age 18-24, and Virginia Department of Health counts of new COVID-19 cases for that 18-24 population for the past three weeks, and then for the past two weeks.

And, for the past three weeks, for the Virginia age 18-24 population:

  • 0.8% were diagnosed with COVID-19.
  • 0.01% were hospitalized for COVID-19.
  • 0.001% died from COVID-19.

For the past two weeks, for the Virginia age 18-24 population:

  • 0.6% were diagnosed with COVID-19.
  • 0.007% were hospitalized for COVID-19.
  • 0.0006% died from COVID-19.

You have to be careful when comparing this to the college numbers because testing regimens may differ.  I would guess that asymptomatic cases are rarely diagnosed in the community.  They would only be found via contact tracing.  Colleges and universities, by contrast, may have a more systematic testing program in place, and so find a larger portion of cases.

That said, the all-Virginia estimate for this young-adult population is close to what we’re seeing in the schools above.  In some sense, that’s reassuring.  It’s not as if going off to college hugely increased risk, relative to staying home.

But William and Mary’s numbers again stand out as higher than expected.  Given the late start date, the William and Mary 1.7% number should be compared to the 0.6% observed in the college-age Virginia population over the past two weeks.

Honestly, I’m still puzzling over the fact that about a third of the students tested at William and Mary were positive.  And that the number of students that tested positive — so far — is running at a rate that’s about three times the community rate.  I’m wondering if they’re getting some false positives, as occurred during one episode last year.

But in another sense, it’s not a huge surprise that the average Virginia university has numbers close to the Virginia average for college-age persons.  To a large degree, we have to be looking at literally the same people.  Virginia colleges have about 500,000 enrolled, excluding one university claiming large virtual enrollment, versus 800,000 in the 18-24 age group.