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April 28, 2021

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KrishnaRao_MD_MS.PNGDistancing in Schools and the Transmission of SARS-CoV-2

Reviewed by A. Krishna Rao, MD, MS

Schools for grades K–12 have been a concerning site for potential transmission of SARS-CoV-2 since the beginning of the COVID-19 pandemic. School closures in early 2020 were the first, tangible societal impact of the pandemic felt by millions of people worldwide and a herald of difficult days to come. However, as students returned to in-person education following these early closures, much of the fear that children would spread SARS-CoV-2 has not been supported by multiple epidemiologic studies, irrespective of rates of community transmission. The absolute risk of infection for both students and staff appears quite low, but mitigations such as physical distancing, masking, adequate ventilation, physical barriers, and cohorting remain important. Physical distancing, in particular, can pose a challenge for schools, and even a small change such as going from 6 to 5 feet can mean an additional 5 to 10 desks in a room, depending on classroom shape and size. However, the minimal effective distance in classrooms is unknown. Consequently, evidence on the effectiveness of physical distancing is an unmet need for policy makers.

In a recent study in Clinical Infectious Diseases, van den Berg and colleagues begin to address this evidence deficiency by evaluating the effectiveness of 3 feet versus 6 feet of physical distancing among 251 school districts in Massachusetts. The study included data captured from 537,336 students and 99,390 staff that attended in-person instruction over 16 weeks from September 24, 2020 to January 27, 2021. The incidence rate ratio (IRR) comparing districts with ≥ 3 feet to ≥ 6 feet of physical distancing between students did not show a significant difference (IRR 0.891, 95% confidence interval [CI], 0.594–1.335). Cases among school staff were also similar, irrespective of physical distancing (IRR 1.015, 95% CI, 0.754-1.365). These differences remained non-significant after adjusting for community transmission measured by incidence (IRR 0.904, 95% CI, 0.616–1.325 for students and IRR 1.015, 95% CI, 0.754-1.365 for staff).

The study was limited to one U.S. region and was unable to quantify or incorporate the effects of other mitigations such as ventilation and adherence to masking and cohorting practices. Furthermore, asymptomatic transmission was not quantified, which may not have posed significant risk to students but could have resulted in spread to the community where high-risk individuals could be exposed. However, a strength of the study with regards to the latter included the sensitivity analysis that re-estimated models excluding districts with surveillance testing programs and still found similar results. Additional strengths included the large number of students/staff, the diversity of environments captured, and results that did not change after adjusting for poverty and race/ethnicity.

While this study alone does not definitively demonstrate that physical distancing at ≥ 3 feet is equivalent to ≥ 6 feet for transmission risk of SARS-CoV-2, it does provide useful evidence for policy makers, which the Centers for Disease Control and Prevention (CDC) has already incorporated into their guidance for schools. As with many aspects of the pandemic, considerations for applying the evidence and CDC guidance to a particular scenario are always in flux. At the individual school level, there remains a need to make decisions based on practical considerations and logistics, the vaccination status of staff and the community, and the emergence of new variants. However, this new evidence that reduced distancing requirements remain safe will come as welcome news to K–12 school administrators who seek to allow the return of more students to on-campus education while effectively continuing to mitigate the risk of SARS-CoV-2 transmission.

(van den Berg et al. Clin Infect Dis. Published online: March 20, 2021.)


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