Sunday, September 19, 2021

Happy to be wrong (Covid update)

Earlier this semester, I thought we likely had out-of-control spread on campus from people with breakthrough cases that were going undetected.

It looks like I was wrong.

The University of Illinois decided not to do surveillance testing this fall semester, instead focusing on regular testing only of unvaccinated people and selective testing of vaccinated people if they were in a place with an outbreak. (I still think that's a mistake - see below). The campus also returned almost all of its students—including a record-size first-year class—and encouraged attendance at several mass gathering events including football games. I expected this combination to be disastrous. And, at first, it looked like I was right.

In the first weeks of the semester, we saw a substantial spike in cases. Despite daily testing numbers that were just a fraction of those from last year, we saw new cases at a rate comparable to the February surge and daily positivity rates as high as during parts of the fall 2020 surge.

Over the past week or so, though, the daily numbers of cases have dropped dramatically—we're currently down to an average of under 7 detected cases per day. What we don't know, because we're not testing everyone, is whether those 7/day constitute all of the cases or if we would detect many more than that if we were testing everyone. That is, would we still see only 7 cases/day if we were conducting 10,000 to 20,000 tests/day necessary for surveillance rather than the 2,000 to 5,000 per day we're currently conducting. Or would the number of cases scale proportionally with the number of tests. 

Aside: We wouldn't even need to test everyone to know—we could randomly select a few thousand vaccinated people to test each week and that would give us an estimate. As far as I know, were not doing that, so we remain blind to what's actually happening. I don't know why we're not doing that sort of testing (other than cost).

 Here are some possible reasons things might be going better than I had expected they would:

  • Maybe high vaccination rates coupled with masking requirements were enough to eliminate spread on campus.
  • Maybe spread from breakthrough cases to people who also are vaccinated is even less likely than thought, so undetected breakthrough cases aren't spreading Covid further (given high vaccination rates on campus).
  • Maybe those people who are most likely to engage in riskier behavior—the ones who were most responsible for the outbreaks in the fall/spring—have extra immunity because they both had covid already and have been vaccinated. So, even if they're taking risks, they aren't getting Covid and spreading it. And, everyone else is doing what they were all of last year, taking appropriate precautions to avoid getting Covid or giving it to others.
  • Maybe breakthrough cases acquired from another breakthrough case are more likely to be asymptomatic, in which case we could have spread on campus but it wouldn't be detected because those students wouldn't seek out a test. (worst case that could be detected via the random sampling strategy I noted above.).

Regardless of the reasons, it's great that case numbers are down, and I hope it means that spread on campus is under control. 

That said, the pandemic is far from over. Illinois Region 6, the set of counties that include Champaign, is hovering around 8% positivity (not great). We still have many county residents hospitalized, and we've seen increased deaths over the past month. Southern Illinois has zero open ICU beds for a 20-county region. Other Midwestern states (e.g., Ohio) are seeing a huge surge, and neighboring states are not taking the same precautions that Illinois is (no indoor mask mandates). 

For those reasons, I'm not thrilled with unrestricted attendance at sporting events (especially the indoor ones). If people who aren't vaccinated attend those events, including those traveling from outside the area, we could see spread from them to the campus or vice versa. I'd like to see UIUC require negative tests or proof of vaccination to attend campus events (just like the United Center will). 

It's a relief and great news that campus appears to be doing relatively well right now. I'm glad that my concerns about the fall semester appear to have been overly alarmist. It'd be wonderful to be proven wrong about that. But, that doesn't mean we shouldn't take precautions, especially when the campus and broader community interact.