Since public health experts first recommended social distance guidelines to reduce spread of the coronavirus, the 6-foot rule has felt like the one constant amid evolving stay-at-home orders, mask guidelines and business openings.
But recent research, which TODAY reported earlier this week, calls its premise — that 6 feet of distance reduces the risk of exchanging air droplets with a stranger — into question.
Engineers at Florida Atlantic University simulated a cough in a lab and used a laser to measure how far droplets traveled. Within 41 seconds, the vapor from the "heavy cough" re-creation reached 9 feet. Others got as far as 12 feet.
The FAU test is tracking what happens to small particles similar in size to the coronavirus. NBC's Kerry Sanders observed that some fell with gravity, others were suspended in midair and some even rose. Based on the findings, FAU's Sid Verma, Ph.D., recommended that if you see someone cough in a public place, avoid that area for several minutes.
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Other research, published in the Journal of the American Medical Association in late March, found that the clouds of droplets that coughs often emit can travel up to 23-27 feet.
Still, the solution isn't necessarily to extend the 6-foot rule to 30 feet or more, according to experts. Here's what epidemiologists and physicians had to say about the effectiveness of the 6-foot rule.
Most transmissions happen in close contact.
Dr. Gustavo Ferrer, a pulmonologist and president of Intensive Care Experts Health Network in Aventura, Florida, continues to recommend 3-6 feet of distance because there's "historical data" to support it, he told TODAY.
"If any patient coughs and you put it in a chamber ... it's going to go down," he explained. "The greater transmission is usually in close contact, and most experts would define that between 3 and 6 feet."
The outdoors aren't risk-free.
Dr. Mary Schmidt, an infectious disease physician and associate professor of clinical medicine at Virginia Commonwealth University's campus in Annandale, Virginia, told TODAY that she's "been saying from the get-go" that "6 feet has not been a realistic recommendation" — in part because this virus is "one of the tinier ones."
Her concerns pertain to the outdoors, which many experts say have a lower risk of exposure than indoors.
"Wind moves (the particles) farther away from the person (coughing), and it can keep them in the air longer," Schmidt said. "As long as these very light, little particles are floating in this air puff, they're being blown further away from the person."
She added, "I think being outside in public places with a lot of people around is just as much a risk as being inside with somebody coughing or sneezing."
There's no 'cut-off' for when you're safe and when you're not.
Donald Milton, professor of environmental health at the University of Maryland in College Park, told TODAY that coughs can create multiple modes of transmission. For the novel coronavirus, this includes touching virus droplets and then touching your face, or inhaling fine aerosol particles with the virus.
As a result, he said the 6-foot rule isn't a "cut-off" but rather "a gradient of gradually decreasing risk the farther away you get."
"It's not like you're at risk at 5 feet and safe at 7 feet," he explained. "Six feet is better than 3 feet, and 12 feet is better than 6 feet."
6 feet is a 'minimum' guideline.
Six feet is a "minimum safe distance" and "not the end all be all," Dr. Eric Cioe-Pena, an emergency medicine physician at Northwell Health in New York City, told TODAY. "Context matters ... If I'm in a closet that's 12 feet long with someone actively coughing, that's a much bigger problem."
He added that the 6-foot rule applies to places where you're likely to encounter asymptomatic people, as you should be "home quarantining" if you're sick.
"(Transmission) rates with 6 feet and casual contact are pretty low," Cioe-Pena said. "For people with symptoms ... there's no safe distance because these symptoms can project aerosols a lot farther."
Social distancing is only one measure people should be taking.
Dr. William Schaffner, medical director of the National Foundation for Infectious Diseases in Nashville, told TODAY that the 6-foot rule is rooted in practicality.
"It's something people can understand," he said, stressing that it's only one measure in a series of recommendations that can slow spread of the virus.
"Nobody anticipates that any individual public health intervention is perfect, but if you put together sheltering at home, social distancing, wearing the masks, doing good hand hygiene ... it will reduce the risk of transmission," Schaffner explained. "Not everyone is doing all of them perfectly, but what we want is most people doing most of them pretty well."
One thing all the experts agreed on is the importance of face masks.
"If the person is wearing a mask, that reduces the distance that the cough or sneeze will go," Schaffner said. "That's the whole purpose of wearing the mask."