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Is 6 feet far enough for social distancing? Here’s what science says

To stem the spread of the new coronavirus, public health officials are recommending that when you enter public spaces, like a park or grocery store, you should wear a mask and keep at least 6 feet away from other people, even if they seem healthy. How did experts come up with those recommendations, and how fail-safe are they when it comes to prevention?

There’s a lot we still don’t know about this virus, and ongoing scientific debate over the specifics won’t wrap up anytime soon. But there are several important practices that can reduce your risk of transmitting or contracting COVID-19:

  • Yes, maintain a social distance of at least 6 feet. Avoid crowded indoor areas like bars and restaurants. Always wear a mask when you enter enclosed public spaces like the grocery store. If you want to socialize with people who aren’t part of your household, spend time outdoors at a distance, and consider wearing a mask for additional protection.
  • Wear a mask. The primary purpose of wearing a mask is to reduce the amount of potentially infectious respiratory particles we release into the air when we talk, breathe or cough. But growing evidence suggests that masks can also protect wearers from developing more severe cases of the virus, because they can help prevent some viral particles from making it into their airways.
  • Keep air flowing indoors. Proper air circulation and filtration decrease the potential for indoor airborne transmission. The more time you spend inside an enclosed space with other people, the more likely it is that the air could contain infectious viral particles. Opening windows and facilitating airflow when you have control over an indoor space and avoiding crowded places altogether — while keeping your mask on — can help reduce that risk.
  • Wash your hands frequently. Scrub them for at least 20 seconds with soap and warm water, and carry hand sanitizer with you for when you don’t have access to a sink.
  • Avoid interpersonal contact if you are sick. If you’re experiencing symptoms of COVID-19, you should avoid entering any public spaces. If you’re symptomatic and live with other people, wear a mask inside your home and isolate yourself as much as possible to protect your family or roommates.

Here’s some of the science behind those guidelines, and why they are important to follow to protect yourself, your loved ones and your community during the pandemic.

Why 6 feet apart?

The 6-foot social distancing recommendation is pulled from guidance designed by the Centers for Disease Control and Prevention for medical providers to prevent the spread of infectious respiratory diseases between themselves and their patients in a health care setting. It’s based on past studies of infection among health care workers, and specific to illnesses like the flu that are transmitted by respiratory droplets released when an infected person coughs, sneezes or even talks. Like the flu, novel coronavirus is believed to be transmitted primarily via those droplets.

“We’re in an unusual time that we’re actually advising [those practices] for people in the community setting, as opposed to people who are in a hospital or a clinic,” said Julie Fischer, a professor of microbiology and immunology at Georgetown University and the chair of the Global Health Security Agenda Consortium, which focuses on responding to the threat of infectious disease.

The World Health Organization has a different recommendation for COVID-19: that people keep a minimum of 3 feet between themselves and “anyone who is coughing or sneezing.” That metric, Fischer explained, is based on research conducted during the 20th century that determined 3 feet is the minimum distance needed to reduce chances of infection for pathogens like bacterial meningitis and rhinovirus colds.

But after SARS-CoV-1 — another virus that is closely related to novel coronavirus — broke out in East Asia during the early 2000s, several studies that examined infection rates of health care workers suggested that a standard 3-foot distance might not be enough.

Those studies “hypothesized that the droplets might have spread as far as 2 meters, or about 6 feet,” Fischer said, based on the observation that medical students and other health workers became infected after being in the vicinity of patients, even if they were no closer than 6 feet.

READ MORE: How to use ventilation and air filtration to prevent the spread of coronavirus indoors

In the years that followed, 6 feet became a standard guideline in the U.S. A 2007 CDC guide that focused on preventing transmission of infectious disease in a health care setting noted that it “may be prudent” for providers to wear a mask within 6 to 10 feet of a patient, “especially when exposure to emerging or highly virulent pathogens is likely.” During the 2009 H1N1 influenza outbreak, the CDC officially expanded its guidance to recommend a minimum of 6 feet of physical distance between providers and patients — a recommendation that still stands.

But whether that number actually holds up with this specific virus is a question that researchers are now pursuing. One study published by MIT in March suggested that “turbulent gas clouds” released by infected patients could travel upwards of 23 to 27 feet. The “locally moist and warm atmosphere” within those clouds, researchers explained, allow respiratory droplets to “evade evaporation” and persist for a longer period of time compared to isolated droplets.

The report concludes that, for health care workers specifically, the use of “appropriate personal protection equipment is vitally important” when caring for COVID-19 patients, even if they remain more than 6 feet away from those patients.

But Efraín Rivera Serrano, a virologist and cell biologist at the University of North Carolina at Chapel Hill, said that even if the respiratory droplets released by a patient can travel those distances in the air, the MIT research doesn’t provide evidence that they remain infectious under those conditions.

In other words, he suggested, there is no need to stay 20 feet away from your fellow shopper at the grocery store.

Fischer noted that 6 feet is by no means a “magic number,” and that droplets likely do spread farther under some conditions. But that metric remains our best estimate yet when it comes to how much distance you should keep between yourself and others in public spaces.

How does novel coronavirus spread?

Infectious respiratory diseases can generally be broken down into two transmission categories: droplet and aerosol. Tuberculosis and measles fall into the latter category, Fischer explained, because they are carried via very fine respiratory particles that can evaporate in the air and allow pathogens to travel farther distances. Because these illnesses are so highly transmissible, it’s impossible to establish a “clear, safe distance” between an infected person and someone who is healthy. (And that’s why widespread vaccination against measles is critically important in order to prevent community outbreaks.)

The World Health Organization initially stated that novel coronavirus is “primarily transmitted” through larger respiratory droplets, which fall to the ground more quickly than their smaller counterparts.

But in July, the WHO acknowledged that short-range aerosol transmission of the virus, particularly in indoor, crowded spaces with inadequate ventilation like a restaurant, choir practice or fitness class “cannot be ruled out.”

That shift came after more than 200 scientists from 32 countries sent an open letter to the WHO arguing that mounting evidence suggests “beyond any reasonable doubt” that potentially infectious aerosols released when a person talks, breathes or coughs, could stay suspended in the air or travel longer distances than larger respiratory droplets.

An August update from the CDC echoed WHO’s statement, noting that “short-range inhalation of aerosols is a possibility,” but maintained that “long-range aerosol transmission” is not supported by current data.

READ MORE: Aerosols may play a larger role in COVID-19 transmission than previously thought

When it comes to well-known pathogens, like the flu, physicians have established a general timeline for when people are likely to develop symptoms relative to their initial infection, and how that corresponds with the amount of the virus in their respiratory tract and thus how contagious they are.

But because novel coronavirus is so new, these timelines are still being studied.

“We don’t know when [people infected with novel coronavirus] are at their peak viral load — when they have the most virus in their respiratory tract to be expelled, compared to when they have the onset of symptoms — because so many people have had what appear to be asymptomatic or very mildly symptomatic disease,” Fischer said.

That’s why social distancing matters. People can contract the virus by touching a contaminated surface and then their face, which is why regular hand-washing for a minimum of 20 seconds is critically important. But the most pressing risk of transmission, Fischer explained, is getting too close to other people — even when you’re outside. Your risk of contracting the virus doesn’t drop when you step into nature.

“I wish there were a really clear answer, like ‘inside is dangerous, outside is safe,’” Fischer said. “But the answer is, being in close proximity to people whose status you don’t know is a risk.”

Why masks are encouraged in public

For those who can’t stay home at all times, evidence suggests masks — though not foolproof — can help catch some larger respiratory droplets released by an infected person. The goal of wearing one is not so much to prevent yourself from contracting the virus, but to reduce your chances of transmitting it to other people. Some newer evidence does suggest, however, that wearing a mask can help reduce the amount of virus that enters your system if you are exposed, which could end up making you less sick.

N95 respirators, on the other hand, are essential pieces of equipment specifically designed to protect providers by filtering out 95 percent of particles from the air that they breathe. The use of these specialized masks are particularly important now, in order to reduce the risk for health care workers of contracting COVID-19 from their patients.

But initially, when the virus was first spreading in the U.S., the CDC instructed the public to avoid wearing face masks. That was for two main reasons, Fischer said. First, experts didn’t want to encourage people to “binge buy” equipment that is so critically important for health care professionals. Second, surgical and homemade masks are “not perfect” at source control, which means they don’t fully prevent respiratory droplets from entering the air and potentially infecting other people.

“Because [surgical masks] don’t fit tightly around the face, when someone sneezes or coughs, the droplets can go around the edges of the mask. [With homemade masks,] you add not only the complication that they don’t necessarily fit very well around the face, but they’re made potentially out of fabrics that don’t have very good filtration capacity,” Fischer said.

READ MORE: Why wearing a mask and breathing in less coronavirus probably means you get less sick

It’s believed that around one in four people who have been infected with the virus may not show symptoms, and Fischer suspects that has influenced the CDC’s decision to recommend masks as a widespread extra layer of risk reduction, paired with social distancing. Other studies, including ones carried out in Italy and Iceland, suggest that 50 to 75 percent of those who test positive for the virus could be asymptomatic.

Evidence suggests that infected people can also be contagious before they start feeling sick, or show telltale symptoms like coughing. Presymptomatic transmission, when people appear healthy but can still transmit the virus to others, is therefore another major concern that underscores the importance of distancing and wearing masks.

“There are so many questions that we’re still trying to answer, but it is, I think, pretty clear from the number of asymptomatic transmissions that someone does not have to be sneezing, or coughing violently, to transmit this virus to others,” Fischer said.

People wearing face masks keep social distance in Washington Square park during the outbreak of the coronavirus in New York City, on April 19, 2020. Photo by Jeenah Moon/Reuters

What could life look like when stay-at-home orders end?

Right now, the U.S. is in the mitigation stage of this pandemic. The point of social distancing and staying home as much as possible is to slow the virus’ spread and keep our health care system from being overwhelmed.

Rivera Serrano noted that viruses are “absolutely nothing” without their hosts — if they don’t have cells to invade, they cannot replicate. Reducing interpersonal contact and wearing masks helps rob the coronavirus of the opportunity to infect new hosts.

But to actually reduce the number of new COVID-19 cases to an amount that officials can manage until an effective vaccine is approved, Fischer said, “significant investments” would have to be made in public health interventions. Effective suppression measures would include aggressive, regular testing for the virus, paired with “contact tracing,” a public health procedure that seeks to identify everyone who’s been exposed to an infected person and may be at risk. After that, officials would instruct infected people to self-isolate so they can’t infect others, while monitoring those who are potentially infected so that they can be quarantined immediately if necessary.

Public health workers across the globe have used these measures to “stamp out” outbreaks of diseases like tuberculosis and Ebola, but the scale demanded by this new pandemic is unprecedented in the modern era.

To Fischer, mitigation vs. suppression offer two paths forward. If the U.S. sticks with mitigation, relying heavily on social distancing to slow the virus’ spread, she predicts that new outbreaks will occur when asymptomatic or mildly symptomatic carriers move into new spaces. In that scenario, we would have to keep vulnerable people “completely protected for months.”

“[But] if we can go the suppression route, there is a chance that, while we will still have to manage outbreaks and still be spending a lot of time and money on diagnostic testing and public health and health care, we can resume something that looks much more like normal business processes,” Fischer said. “I still don’t know that we’re going to have concerts or large sporting events or crowded markets for many months, but we can at least return to normal more quickly.”

The mitigation efforts adopted by most of the U.S. so far have had an enormous economic impact on people and businesses. But to quickly return to the way things were before social distancing and stay-at-home orders, Fischer warns, would undo much of the efforts already made to “flatten the curve.”

The public has heard mixed messages from officials at the state and federal levels about best practices for fighting this pandemic, Fischer said, acknowledging how frustrating that can be. As our knowledge of the virus evolves, so too will the guidance recommended by public health officials — that’s why the CDC updated its position on wearing masks in public. In the meantime, she explained, you can protect yourself and your loved ones by seeking out trusted sources for information, understanding the differences between evidence and opinion, and making your own risk assessments when coming into contact with other people.

“Ultimately, it’s up to each of us. It’s up to our discipline, it’s up to our risk assessment,” Fischer said. “It’s up to us being the solution and understanding that data changes as we go along and that we [interpret it,] think about what it means in terms of risk, and move on as best we can.”