Six Is Not a Magic Number
Three feet of distance in schools is plenty as long as other anti-COVID safety measures are in place. Here’s why.
In order to return K–12 students to in-person learning five days a week, kids will have to be spaced closer than six feet apart from one another. There simply isn’t enough room in most schools otherwise. Fortunately, standard anti-COVID safety measures can keep kids, educators, and staff safe even at three to six feet of distance.
Where did the six-foot rule come from?
Let’s start with a reminder: the six-foot rule was developed without taking masks into account. It’s based on the idea that the coronavirus is transmitted primarily by what scientists call “large droplets”: heavier bits of moisture that fall to the ground right away and don’t tend to travel farther than six feet from unmasked people. But over the last year it’s become clear that large droplets aren’t the only way that COVID-19 is transmitted.
What are aerosols, and why do they matter?
Unlike large droplets, which fall quickly, aerosols are extremely small, light micro-droplets that can float in the air for a long time. We know that the coronavirus can be transmitted by aerosols because of evidence from superspreader events such as the Skagit Valley Chorale rehearsal in March 2020.
If COVID-19 could only be transmitted by droplets, we would expect that only people sitting within six feet of the infected singer would have gotten the virus. But people throughout the room got sick, even those who never got close to that unfortunate person and never touched anything they touched. Those folks got sick because they breathed in aerosols carrying SARS-CoV-2, the virus that causes COVID-19. None of them were wearing masks.
Good masks can block lots of aerosols as well as large droplets.
Masks work best when they fit snugly and don’t leave gaps, as a recent CDC study demonstrated: wearing a surgical mask knotted and tucked increased its ability to block aerosols to 96%. Fitted three-layer cloth masks can do the trick, as well: they block more than 90% of aerosols if their middle layer is made of the same kind of non-woven material that surgical masks are made of (vacuum-cleaner bag material works well).
We also have real-world evidence that wearing masks can drastically decrease COVID-19 transmission. A December 2020 review cited seven different papers showing that mask-wearing and mask mandates decrease infection rates. One of those studies was a July report from the CDC: a Missouri hair salon in which two hair stylists who were wearing masks cut 139 people’s hair while the stylists had symptomatic COVID-19.None of their clients tested positive.
Ventilation dilutes aerosols.
You can’t get COVID-19 from inhaling just one or two aerosolized particles. It takes a lot. So one critical way to make an indoor space safer is to push the potentially infected air out and pull some clean air in. In other words, ventilate the room.
The ventilation doesn’t need to be high-tech. In one study of schools in New York City,the likelihood of COVID-19 transmission was lower in older school buildings – some of them over 100 years old – than it was in newer ones, simply because the elderly buildings were drafty. Even installing an outward-facing window fan can make a big difference. According to Ian Colbeck of England’s University of Essex,just opening the windows can “reduce the risk of infection from particles by more than 70%.”
Screening is source control.
The best way to keep infectious droplets and aerosols out of a room is to prevent contagious folks from entering the room to begin with. That’s called source control. In the school setting, part of source control is making sure that people with coronavirus symptoms don’t come to school.
However, since people can be contagious before they show symptoms - or may never show symptoms at all - another critical layer of source control is screening in-person students, educators, and staff for COVID-19. This piece is likely to become even more crucial as more-transmissible variants sweep across the country.
Once you’ve lowered your overall risk,
the difference between three and six feet is negligible.
As we discussed above, wearing masks, ventilating rooms, and screening people all lower the risk of COVID-19 transmission. Physical distancing decreases the risk even further. But with all those other safety measures in place, the distance between people doesn’t have to be as wide.
The graph shown here comes from a large meta-analysis from The Lancet, Britain’s premier medical journal. The researchers looked at 172 different studies, which together provided results from over 25,000 people around the world. The X axis is distance in meters. The Y axis is your risk of getting COVID-19. The lines on the graph show that the greater the distance between people, the lower the risk of getting the coronavirus.
But take a look at the red and green lines on the graph, which show what happens to your risk of infection once your baseline risk is either intermediate (red) or low (green). In either situation, moving from 1m of distancing (about 3 feet) to 2m of distancing (about 6 feet) barely changes your risk at all.
While I was writing this article, a study was published that provides real-world data to go with The Lancet’s analysis. It looked at data from 251 Massachusetts school districts, comprising over half a million students and nearly 100,000 teachers and staff members. All the schools required masking; more than 90% had improved their ventilation in some way. There was no significant difference in the COVID case rates of schools at three vs. six feet of distance. And every single school district’s COVID incidence rates were lower than the incidence rates of their surrounding communities.
Schools are not perfect, and they’re not magic. But they’re necessary. We know what we need to do to make schools safe enough for kids and teachers to attend in person; it’s all right here. If we do what we need to do, it’ll work. Even at only three feet of distance.
Special thanks to Suzie Clarke Allen, MSN, C-PNP; Melea Atkins, MBA; Andrea Ciaranello, MD, MPH; and Rosy Hosking, PhD, for their assistance on this article.
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