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.