Post #1086: William and Mary COVID-19 outbreak, update to 3/31/2021

Posted on April 1, 2021


This post is another brief update on the William and Mary COVID-19 outbreak.

William and Mary continues to post student COVID-19 test results a few hundred at a time.  Ysterday’s batch of about 200 tests identified eight new COVID-19 cases.

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

The only interesting change is that the last batch of tests showed a 3.9 percent positivity rate.  The difference between that and the 1.4 percent rate for the first batches of tests is unlikely to have arisen purely by chance.  So that last batch of tests is different from the first ones, but there’s no way to guess why it’s different.  It’s a small number of new cases no matter how you slice it.

Below, here’s how this looks when I compare the cumulative cases at William and Mary to the count you would have expected, based on the average incidence of COVID-19 in the 20-to-29-year-old population of Virginia.  As of today, William and Mary is now about 50 percent above that expected rate.

With a little over a month to go in the semester, short of some massive outbreak in Virginia as a whole, that’s about the way this will end up.  At the community (Virginia 20-29 year old) rate, you’d expect to see about one new case a day for a population the size of the W&M enrollment.  I’m guessing it will be a while before William and Mary gets the daily increment down to one case per day.  So the gap between the actual and expected case counts will probably continue to increase for much of the rest of the semester.