COVID-19 Transmission in Classrooms?

Dear Colleagues,

Faculty and students are continuing to express concern about the safety of face-to-face instruction while the omicron wave is hitting our communities. Recent statements by the President and Provost about finding no cases of in-class transmission are viewed with incredulity. Afterall, most instructors have knowledge of students missing class presumably due to COVID-19 infections. How could in-class transmission not be a huge problem?

Omicron is a highly infectious variant of the SARS-CoV-2 virus that has been sweeping across the U.S. and displacing the delta variant. A recent report from the CDC evaluated COVID-19 patients from a single hospital in Los Angeles (about 1,000 patients) and found that a higher proportion of vaccinated people were hospitalized during the omicron period compared to the time dominated by the delta variant, which is likely due to the antigenic mismatch between vaccination and the omicron spike protein. Nevertheless, for December 2021 the rates of infection for vaccinated and boosted (148.6 people per 100,000), and vaccinated but not boosted (254.8 people per 100,000) people were much lower than unvaccinated people (725.6 per 100,000).

The recent recommendation by CDC to use higher quality masks (e.g., K95 and KN95) reflects the recognition that omicron is more infectious, probably because more virus is shed and thus a better mask is going to work better than a cloth mask. One way to appreciate this fact is the R-naught (R0) for these strains. R0 indicates the infectivity of a pathogen. The first strains of SARS-CoV-2 had an R0 value of about 3.3, meaning that if people mixed freely and without barriers or immunity, one infected person would infect an average of 3.3 additional people. The delta variant upped the game with an R0 of between 5 and 7. Omicron hit the jackpot with an R0 of between 7 and 14 (10 seems to be the growing consensus). Measles, which is the most transmissible virus in the human population, has an R0 of between 12 and 18. That is, by some measurements, omicron is as infectious as measles.

Consequently, why wouldn’t you expect transmission to be rampant in a college classroom? WSU has worked closely with Whitman County Public Health to conduct contact tracing during the omicron wave. If classroom transmission was occurring frequently, they should have found multiple cases where an individual’s infection could only be explained by sharing a classroom with an infected individual. In fact, for 95% of the cases investigated, contact tracers found that infections could be explained by shared housing and social interactions, not a classroom. The other 5% were ambiguous because there was no way to clearly separate classroom contacts from housing and social contacts.

Put another way, if 5% of cases were due to in-class transmission, you would have to trace at least 60 cases to have a 95% probability of finding just one in-class transmission case. For the month of January alone, contact tracing for WSU students exceeded this by ten-fold. That is, with nearly 600 investigated cases, there hasn’t been one that is unambiguously due to in-class transmission. Does this mean that in-class transmission is not happening at all? Probably not, but it certainly means that in-class transmission explains very little of the omicron cases on campus.

The WSU population has a vaccination rate of >95% and the number of cases in a 10-day infection period dropped from about 250 to about 100 in the past two weeks. Furthermore, on-demand student testing peaked between January 20th and January 26th with 150-170 tests per day. For the remainder of the month the number tests dropped to 90 or less and positivity dropped from a high of approximately 60% to 20-30%.

Contrast this with the county at large that has a vaccination rate of around 42%. Case counts have skyrocketed to roughly 3,000 per 100,000 individuals. Assuming a campus census of 20,000 people, an equivalent rate on campus would require 600 cases, or six times more than what is being reported. The take-home message is that vaccination, even if not a perfect match to omicron, really works, as does masking. Furthermore, faculty, staff and students should Photo of Faculty Senate Chair, Doug Callbe far more concerned about community transmission of omicron than classroom transmission.


Douglas Call, Faculty Senate Chair

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