Monday, August 30, 2021

Covid at Illinois - 30 August 2021

During the 2020-2021 academic year, I posted regular updates about Covid at the University of Illinois. I tracked the number of positive cases on campus, estimated the percentage of students infected, and computed various metrics of the infection that were more meaningful than the ones provided by the university (e.g., rolling averages of cases, cumulative cases by semester, cases by week, etc.). Those analyses were necessary because the campus dashboard featured meaningless statistics like 7-day average positivity and the all-time number of tests, neither or which provided useful information to gauge the extent of outbreaks. The campus dashboard also gave no breakdown of the infection percentages, the numbers of students being tested each week, the compliance rate for testing, etc.

In addition to those daily updates, I also discussed many of the logistical problems that contributed to the infection of an estimated 20% of the undergrads on campus last year (4935 out of about 24000) as well as some of the misleading claims coming from the administration. In addition to the daily summaries, I posted a detailed summary of the fall semester issues as well as a more in-depth analysis of how delayed testing results likely contributed to the fall 2020 surge. 

This year, changes in testing policies (not testing everyone) mean that I won't be able to estimate the infection rates on campus, and it will be much harder to evaluate whether or not we're in the midst of a large outbreak. It'll be more guesswork than analysis. I'll try to do that guesswork and will post updates here on my blog. Occasionally I'll post analyses as well. But, there's not much benefit to the sort of daily tracking I did last semester because there won't be enough information available on the campus dashboard to do it. I fear that we're running blind this semester. Here's where things stand on campus and why we won't have the information we need.

Vaccine "requirement"

This summer, the campus announced that they would be requiring vaccines. That sounded fantastic, but it turned out that the implementation had no teeth and it was actually more of a "nudge" than a requirement. If you weren't vaccinated — and you didn't need to give any reason why not — you had to continue testing. 

Last week, Gov. Pritzger announced that all school and university faculty and staff in Illinois must be vaccinated. Shortly after that announcement, the university announced that they will now mandate vaccination for everyone (except those with a medical or religious exemption). I had thought that "requirement" and "mandate" are synonyms, but apparently they mean different things to our administration. I also have no idea how hard it is to get a religious exemption. In my view,  you should be required to present a holy text from your faith showing that vaccines are not permitted...). In any case, it's great that we finally have an actual vaccine requirement/mandate coming into effect. 

Changes to testing

Last year, the campus tested everyone twice weekly (allegedly - there was a lot of non-compliance). Over the summer, when cases were low and vaccines were available, the university developed their plan for the fall: They dramatically scaled back on testing by only requiring unvaccinated people to test. The number of testing sites was reduced to 4. The used vaccination as a get-out-of-testing incentive. Unfortunately, they didn't radically change their plans for Delta. They did increase the required testing frequency for unvaccinated undergraduates to every other day because modeling showed that without doing that, people would spread Delta before they knew they were positive. Delta becomes infectious faster than the earlier variants. 

However, by electing not to test vaccinated people on campus, we won't detect breakthrough cases (unless they are symptomatic and elect to get tested, by which point it's too late to stop spread). We also won't be able to break the chain of transmission by isolating infected students and quarantining or testing their contacts. We're going to be largely blind to the outbreaks on campus, and they could easily get out of control. The campus has the capacity to test everyone, but they chose not to use it. It's a potentially disastrous decision. Here's why.

The consequences of testing only the unvaccinated

There are far more vaccinated students than unvaccinated ones on campus. About 88% of students are vaccinated, and that soon will be closer to 100% now that we have an actual mandate. If we estimate vaccine efficacy against infection to be approximately 60%, that means there will be nearly 3x as many breakthrough cases than there are cases among the unvaccinated!

To see why, imagine that we test all of the unvaccinated students on campus on a single day and that 1% of them test positive. If we assume that the unvaccinated and vaccinated students had the same exposure to covid via close contacts, that means 0.4% of the vaccinated students would have tested positive had we tested them too (60% efficacy against infection). With about 35,000 undergrads on campus, about 30,800 of them are currently vaccinated (88%) and the remaining 4200 are unvaccinated. If 1% of the 4200 tested positive, that would yield 42 cases. If 0.4% of 30,800 vaccinated students tested positive, that'd be 123 cases. So, we should expect about 3x as many cases among the vaccinated population as among the unvaccinated population. There are a lot more vaccinated than unvaccinated students (which is great, of course). 

In the extreme, if 100% of students were vaccinated, and we're only testing unvaccinated students, we could have a massive outbreak on campus via breakthrough cases and we'd know nothing about it (until people start showing symptoms and seek testing or treatment. But by the time they're showing symptoms, they've been infectious for a while).

Last year, the University was (somewhat) able to contain outbreaks by quickly identifying positive cases—often before they were infectious—and then isolating them. We saw the surge, implemented mitigations, and brought numbers down at least somewhat. This semester, up to 3/4 of the initial cases could go undetected. Unlike last year, we'll be blind to spread from those cases until it's too late to stop it. 

Vaccines are highly effective at preventing severe illness, hospitalization, and death. And, students might be at lower risk than older people as well. But, the vaccines aren't airtight protection, and even with the campus's indoor mask requirement (again, that's great!), there are many opportunities to spread Covid both on and off campus (see the massive unmasked crowds at the football game, at bars, etc.). If the University allows unmitigated spread on campus, it likely will reach the broader community this semester. 

As was the case last year, the University of Illinois is in much better shape than many other universities. First, Illinois is in better shape than many other states. We have a governor who is implementing good public health policies (mandating vaccines for all schools and requiring masking indoors) and a local health district that is proactive and communicates well. We have a campus mask mandate and are implementing a vaccine mandate. Due to the amazing test that researchers developed here and the testing capacity that was built up over the past year, we have the potential to know a lot more about how bad the outbreaks on campus are and to end them before they spread too far. We have the capacity to limit the spread and consequences of Delta, but we're not doing everything we need to be doing.

Even if the University prefers not to test everyone due to costly logistics, there are approaches we could take that would help at least determine how much spread we have on campus. For example, the campus could test randomly selected, somewhat large subsets of vaccinated students each week. If those tests revealed a high rate of positives, we might need to adopt more extensive testing and restrictions. The dashboard could also separate results for vaccinated and unvaccinated people. That would show whether we're seeing a spike in vaccinated people seeking tests (a sign that we have spread). Without some form of systematic surveillance testing, though, we won't know how bad things are until people start getting sick.