Post #1099: William and Mary, final St. Pat’s update

Posted on April 7, 2021

William and Mary’s COVID-19 dashboard added just over 150 new tests and no new positives cases yesterday.

By my count, they have fewer than 200 students left to test.  That’s close enough that I think we can sum this up.   Overall, about 130 students were found to test positive during this period.  You should plausibly subtract 15 from that to account for the ongoing trend (the likely increase in positives you’d have seen if this outbreak hadn’t happened), and say that somewhere around 115 students tested positive because of this outbreak.

Up to now, I’ve tracked “test positivity”, which is the fraction of tests that were positive.  But with multiple tests per student over the course of the semester, the right way to wrap this up is in terms of the fraction of students that have been infected while on campus.

At the start of the outbreak, just (143/6660 =) 2.1% of students had been infected while on campus.  By the end of the outbreak, that had risen to (284/6660 =) 4.3% of students.  That final number is about 50% higher than I would have expected to see based on the “community rate” (the average rate of infections for Virginia residents age 20 to 29) over this period.  And so, unlike last semester, I can’t claim that my daughter was actually safer at college than if she’d stayed home.

Barring any unforeseen change, I think this will be my last update on William and Mary’s St. Patrick’s Day outbreak.  I’ll go back to checking the dashboard from time to time.

On a less cheerful note, my daughter reminded me that W&M students have a couple of Spring Break days this week.  (April 6th and 7th).  She expects to see another outbreak following that.  W&M has scheduled their next round of census testing of the student body starting 4/14/2021.

If there is a spring break outbreak, the new positives should start showing up early next week.  At the minimum, assuming nothing else happens, I’ll check in again at that time.