The current guidance for safe social distancing may not be enough to stop the spread of COVID-19, a new analysis suggests.
In the report, researchers from the Massachusetts Institute of Technology and the University of Oxford say other factors, such as ventilation, crowd size, exposure time and whether face coverings are worn, need to be considered, as well.
Since the beginning of the pandemic, the advice has been to keep at least 6 feet away from other people indoors and outdoors. "COVID-19 spreads mainly among people who are in close contact (within about 6 feet) for a prolonged period of time," according to the Centers for Disease Control and Prevention.
However, in the report, published Tuesday in The BMJ, the researchers wrote that "physical distancing should be seen as only one part of a wider public health approach to containing the covid-19 pandemic."
Lydia Bourouiba, an associate professor of civil and environmental engineering at MIT and co-author of the report, said, "It's not just 6 feet and then everything else can be ignored or just mask and everything else can be ignored or just ventilation and everything else can be ignored."
It's important to distinguish between high-risk and low-risk exposure, Bourouiba said.
Some evidence suggests that the coronavirus may travel more than 6 feet through activities like coughing and shouting, the researchers wrote. In the highest-risk situations, such as indoors with poor ventilation, large crowds, prolonged contact time and no face coverings, distancing beyond 6 feet should be considered. Locations that fall under this category include bars, stadiums or restaurants. In low-risk scenarios, such as in outdoor spaces with few people nearby, less stringent social distancing should be adequate.
The researchers developed a color-coded chart to show how transmission occurs, based on different types of exposure.
"This is a way to synthesize and, in some sense, translate complex notions into what we hope is an accessible color-coded chart," Bourouiba said.
Dr. Ezekiel Emanuel, a bioethicist, agreed that the public needs a better sense of risk level of various activities. Emanuel, who wasn't involved in the new research, said coronavirus infection risk boils down to four factors:
indoors or outdoors
whether heavy breathing, such as shouting or singing, is involved
"If you're outdoors, not in a crowd and not going to be with other people for prolonged periods of time, that's probably good," said Emanuel, an oncologist who is vice provost for global initiatives at the University of Pennsylvania. "Is it a zero-risk scenario? Nothing's zero-risk. Is it a low-risk scenario? Yes."
Evidence suggests that the 6-foot distance should be the minimum indoors, said Linsey Marr, a professor of civil and environmental engineering at Virginia Tech.
"People have put too much weight on 6 feet as being this dividing line between risky and safe. And this clearly shows we've known that 6 feet is a guideline but that the farther the better," Marr said.
Marr, who studies how the virus could be spread through aerosol transmission, said that contrary to guidelines, everybody should be wearing masks when indoors even if they are 6 feet from others.
"I've seen a lot of guidelines that say wear a mask if you can't maintain distance, but I think that we need to be wearing a mask at all times when we're indoors with other people outside of our own homes," she said.
Time of exposure is also very important, as simply passing by somebody in a grocery store with both patrons masked is a low-risk exposure, Marr said.
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Eleanor Murray, an epidemiologist at Boston University School of Public Health, said the new data could be helpful for public health officials.
"This is just a nice summary of some of the nuances that everybody who works in the area of outbreaks is aware of but has been having trouble conveying to the people that need to make the decision," Murray said.
And Murray and other epidemiologists believe that as students return to classes, school officials need to think beyond the 6-foot guidance.
"If they're sitting in that room — even if they're 8 feet apart — if they're sitting in a room for four hours together or two hours together, then that's increasing their risk, even though they don't have that necessarily very close physical contact," she said.