Study shows how mitigation measures limited COVID in class

In the fall of 2021, Boston University in the United States was able to reduce in-class transmission of SARS-CoV-2, the virus that causes COVID, to negligible levels by mandating masking and vaccination, and improving air filtration or opening windows, says a first-of-its-kind study that combines surveillance testing, contact tracing and genome sequencing of positive cases of COVID.

According to the study published on 5 August by the American Medical Association in its on-line journal, JAMA Network Open, the more than 600,000 polymerase chain reaction (PCR) tests conducted over the course of the fall 2021 semester found that only 850 of the university’s 33,000 faculty and students were infected with SARS-CoV-2.

Contact tracing linked only nine of the 850 cases to the more than 140,000 in-class events that fall, for a potential transmission rate of only 0.0045%.

“Then when we looked under the hood at each of the small number of potential transmission events,” says John Connor, associate professor of microbiology at the Boston University School of Medicine and co-author of the study, “the viral genome said that it was wildly improbable that those situations were in-class transmissions”.

Mitigation measures

Prior to resuming in-class instruction in the fall of 2021, Boston University took a number of measures to mitigate the spread of COVID-19. Filters for the classrooms and lecture halls that are mechanically ventilated were upgraded, and the HVAC (heating, ventilation and air-conditioning) systems were set to allow the maximum number (two or four) exchanges of air exchange per hour.

When weather permitted, windows were opened, and when they could not be, commercial grade HEPA (high-efficiency particulate absorbing) filters were turned on.

Boston University required all students, faculty and staff to be vaccinated, save for those who had either religious or medical exemptions. Rates for each group were above 94%. The university also required masking for all indoor activities, though, if they were more than six feet away from students, faculty were permitted to remove their masks.

Additionally, the university instituted on-campus surveillance testing and required students who tested positive to quarantine, and also conducted contact tracing. Of the more than half a million PCR tests conducted, fewer than 0.1% tested positive for the Delta variant that was then circulating in the United States. These swabs were sent to Connor’s laboratory, which sequenced the genome.

Real-world testing

Before the study, titled “Examination of SARS-CoV-2 in-class transmission at a large urban university with public health mandates using epidemiological and genomic methodology”, studies trying to determine transmission in settings such as classrooms were based on theoretical calculations.

“To my knowledge,” says Connor, “nobody had put people in a room with a known number of positives, where they marked off separation and did a real-world test.”

What made the Boston University study possible, Connor told University World News, were three things. First, because the university had undertaken surveillance testing, they had data in real time from the entire university cohort and not just clusters that are discovered after the fact, ie, after someone realised they had become ill.

Second, the university’s contact tracing group determined where people who tested positive had been.

“Once we knew that there were very, very few cases of COVID that could have been contracted in class, as opposed to in dorms or in social settings, the question became whether these cases of COVID were caused by the same lineage of the Delta variant. This is where genomic sequencing came in [the third thing],” he says.

From the point of view of a student with COVID, which ‘grandson’ or ‘granddaughter’ of Delta they had is not particularly relevant. For Connor’s study, however, which of the more than 12 lineages identified on the campus a student had was vital.

“Let’s assume you have two people that go to the same class. And they both test positive for SARS-CoV-2. If one has one and the other has another lineage, we can be almost certain that they were not infected in class,” he explains.

“However, if they have the same lineage, then one could have infected the other. But, if there are no other infections in class, and from contact tracing we discover that they share a dorm, the idea that the transmission happened in a room where they spend probably 12 times as much time together than in class can be deemed the most likely site of transmission.”

Correlation with state figures

One of the most interesting findings of the study was that though the number of cases at Boston University was much lower than in the state of Massachusetts – between 6 and 28 vs 500 and 1,300 on charts that record the seven-day rolling mean – the graph of cases on campus more or less tracks the graph for the state as a whole.

The number of cases at Boston University moved in the range of eight to 12 between when school started in September until early December, while the figure of the state was roughly 500.

In early December, both charts show a steep rise – to almost 30 cases of COVID at Boston University and some 700 in the state.

“What you are seeing there,” Connor told me, “was the influx of cases due to the Omicron variant. It’s a reflection of what’s going on outside Boston University, which is a university without walls in a dense urban setting where there is a great deal of mixing between students, faculty, staff and the entire community around the university.”

It’s notable, however, that even after Omicron displaced Delta at Boston University and the cases did rise, there was still negligible risk to students who had been vaccinated and followed masking protocols.

This fact underscores what Connor wrote at the end of the study: “Our data supports the hypothesis that a combination of SARS-CoV2 vaccination and risk mitigation measures, including indoor masking, regular surveillance testing and enhanced air filtration, can be highly effective at limiting disease spread within a large university academic environment to the extent that the classroom transmission is negligible,” writes Connor.