The answer, it turns out, is far. By now, most of us know the Centers for Disease Control and Prevention (CDC) recommendations for lowering the risk of contracting COVID-19: Wash your hands regularly for at least 20 seconds (or use hand sanitizer when you can’t), stay home as much as possible (and definitely when you are sick), wear a cloth face covering in public, and stay at least six feet (two arms’ length) from other people.
How ‘6 Feet Distance’ Guide Became Standard
The six-feet recommendation is a longtime standard for viruses, which are primarily transmitted by large droplets spewed from the mouth of a person who is sick, says Irfan Hafiz, MD, an infectious disease specialist and chief medical officer at Northwestern Medicine Huntley Hospital in Huntley, Illinois. “Most large droplets that carry COVID-19 will fall within that distance,” he says. But a rash of new research is raising questions about whether six feet is always sufficient. And in a number of situations, it seems the answer is no. “Six feet is good, but 10 feet is better,” concludes Joseph Allen, DSc, director of the healthy buildings program at Harvard’s T.H. Chan School of Public Health in Boston, in an op-ed in May 2020 in the Washington Post. RELATED: 10 Misconceptions About the Coronavirus
Coughs and Sneezes Fly Farther Than You Think
Droplets and other particles emitted from your mouth when you cough vary in size. “Gravity pulls the larger particles to the ground within a short distance, but smaller particles can be carried farther in the air,” Dr. Dhanak says. He and his team simulated coughs in a lab with these smaller particles spewing from a mannequin. They used laser lights to visualize the distances traveled. They found that a heavy cough sends particles out six feet in roughly 12 seconds, and nine feet before a minute is out, according to their study, published in the June issue of Physics of Fluids. The heaviest coughs pushed the germs as far as 12 feet. What’s more, some particles lazily lingered in the air for a minute or more. RELATED: How Obesity May Increase the Risk of COVID-19 Complications Other researchers have added wind to their calculations and found coughs can go even farther. A report published in May 2020 in the Physics of Fluids showed that a mild cough in low wind propels droplets 18 feet in just five seconds. “Considering the environmental conditions, the [six feet] social distance may not be sufficient,” the authors, from the University of Nicosia in Cyprus, concluded. In fact, when researchers at the Massachusetts Institute of Technology (MIT) took an image of a sneeze, published in August 2106 in The New England Journal of Medicine, they found that smaller particles remain suspended in the air and can travel up to 26 feet in a few minutes. Of course, with each foot of distance from the person coughing or sneezing, fewer droplets head your way. “The number of droplets gets diluted over distance. So the risk decreases the further you are, although it is still there,” Dhanak says.
Tiny Particles From Your Body Also Hang in the Air
These droplets, produced when an infected person (whether showing symptoms or not) coughs, sneezes, or talks, “can land in the mouths or noses of people who are nearby or possibly be inhaled into the lungs,” the CDC website explains. RELATED: Will the Protests Roiling America Fuel New Coronavirus Outbreaks?
Aerosols Are Lighter, Go Farther
But experts are now coming to understand that particles even smaller than droplets, known as aerosols, might also spread the disease. Because aerosols are lighter than droplets, they remain airborne longer and they spread farther away, Dhanak says. This means you can potentially catch the novel coronavirus even if a person six feet from you doesn’t cough or sneeze. Simply talking can spread these germs, with louder speech even riskier, reports researchers at the National Institutes of Health and the University of Pennsylvania in a paper published in May 2020 in the Proceedings of the National Academy of Sciences. Just a minute of loud speech generates “at least 1,000 virion-containing droplet nuclei that remain airborne” for more than eight minutes, they conclude. RELATED: COVID-19: Protecting Our Mental Health While We Ride Out the Pandemic
Indoor Air Flow Is Yet Another Factor
Exactly how far droplets or aerosols travel seems to vary by the situation. In general, being outside helps limit transmission because the particles disperse faster. This is why experts say summer outdoor activities are generally safer — although even here you should observe ample social distancing, Dr. Hafiz says. If you’re inside, many factors play a role, including whether the air-conditioning (AC) is on and what direction it is flowing. This was shown in the early release of a study scheduled for publication in July by the CDC of a superspreading event in a restaurant in China, where a person who didn’t know they were infected ate. Diners at three tables on one side of the restaurant, some farther than six feet, later developed COVID-19, while those sitting elsewhere did not. The authors conclude that the AC system, which blew on that side of the restaurant, likely spread the disease. “Strong airflow from the air conditioner” could have sent the virus from table C to table A, then to table B, the authors report. You’ll want to increase your distance as much as you can while indoors, where most virus transmission takes place, Dr. Bromage says. Still, “dose and time” are both needed, so simply blitzing through someone airstream is less likely to make you sick than hanging around for hours, he observes. RELATED: 7 Home Remedies to Stop a Bad Cough
Don’t Run or Bike in Someone Else’s Wake
Even outdoors, six feet of distance does not offer sufficient protection if you’re exercising near others in a crowded park or neighborhood, wrote Joel N. Myers, PhD, founder and CEO of AccuWeather, in a blog. Walking a brisk 4-mph pace is equal to moving six feet each second, while biking at 15 mph is like 22 feet per second, he notes. If you and another exerciser are moving in the same direction at those speeds, “you probably should be at least 20 or 25 feet apart” for brisk walking, “and more like 30 to 40 feet apart” for biking, he writes. In a preprint study, other researchers suggest more than six feet of distance is needed if you run, as is avoiding running directly in another person’s slipstream. Instead choose a more staggered or side-to-side arrangement. RELATED: Your COVID-19 Testing Guide: Nasal-Swab Tests, Antibody Tests, Saliva Tests, and More
Masks Help Limit How Far Droplets Travel
When someone wears a face covering when they cough or sneeze, this does lower how far the germs travel, Hafiz says. “An infected person who wears a face mask can significantly reduce the spread of the virus,” he says. But it doesn’t stop it entirely. At least one small study from South Korea, published in April 2020 in the Annals of Internal Medicine, found smaller particles of virus escape a cloth covering during a cough. Dhanak’s research similarly found viral particles penetrate cloth masks, although none gets as far as six feet, so this distancing may be sufficient if everyone is masked. But with COVID-19 causing potentially serious complications, it pays to go beyond the six feet recommendation whenever possible. “The farther away you can be from potential sources of infection, the better,” Hafiz says.
