Social distancing is the most effective way to slow the spread of the coronavirus — more so than face coverings and eye protection — according to a meta-analysis published Monday in The Lancet.
The findings have new significance as thousands of Americans are gathering alongside strangers in the midst of the pandemic, demonstrating against the death of George Floyd and demanding an end to social injustice.
"We just spent 93 days limiting behavior, closing down, no school, no business, thousands of small businesses destroyed," New York Gov. Andrew Cuomo said Monday, "And now? Mass gatherings, with thousands of people, in close proximity?"
"What sense does this make?"
Chicago Mayor Lori Lightfoot echoed the frustration and concern Monday. "We worry about thousands of people that have been out in the streets over the last few days," she said. "God forbid we see a spike that overwhelms our health care resources, just as we saw the light at the end of the tunnel."
Covid-19, the disease caused by the coronavirus, spreads mainly through close contact, particularly large respiratory droplets from sneezes and coughs — as well as shouting and yelling. Tear gas, employed by some law enforcement officers to control crowds, can also lead to intense coughing.
Those respiratory droplets spread the virus when they come into contact with the eyes, nose and mouth of other people.
"There's an ongoing, real risk of infection," said Dr. Holger Schünemann, a professor of medicine and clinical epidemiology at McMaster University in Canada. "Just by logic," he said, referring to the protests in the United States, the "situation does increase the risk of some spreading of the virus."
Schünemann and his colleagues reviewed and analyzed 172 studies to assess how well infection control measures have worked to control Covid-19, as well as two other coronaviruses, SARS and MERS.
They found that staying at least 3 feet away from others cut the risk of transmission to 2.6 percent, down from 12.8 percent, among those in closer physical contact. The study authors added that distances of 6 feet could be even more effective.
The Centers for Disease Control and Prevention recommends social distancing, as well as avoiding mass gatherings and crowded places, to cut the risk of Covid-19 infections.
The spread of infection in crowds has been shown before, particularly during the 1918 influenza pandemic.
When the first cases of the flu were reported in Philadelphia on Sept. 17, 1918, authorities "downplayed their significance and allowed public gatherings to continue," according to a 2007 study in the Proceedings of the National Academy of Sciences.
One such gathering included a large parade in the city on Sept. 28. By the time officials in Philadelphia started limiting large crowds on Oct. 3, it was too late. The virus had spread unchecked through the city, with nearly 50,000 cases and 12,000 deaths.
Infectious disease experts now worry history is repeating itself, with similar scenes that appear to be playing out in cities across the U.S. — not only among protesters, but also from people moving quickly back to "normal life."
"Protests tend to be very finite in time," Dr. Colleen Kraft, the associate chief medical officer at Emory University Hospital, said. "These types of mass gatherings tend to be shorter lived than what I'm seeing from vacationers on beaches."
"I really am more concerned about the way that people have gone back to where they aren't using any type of personal protective equipment when they're interacting with others," she added.
Schünemann's analysis also found some benefit to face masks and even eye protection to protect against coronavirus infections.
Appropriate use of face coverings and eye protection reduced the risk of infection spread as well, though not as much as distancing. Eye protection included both goggles and face shields, such as the ones used in health care settings.
But nothing guaranteed a stop to the spread: "No intervention, even when properly used, was associated with complete protection from infection," the study authors wrote. That means attending a gathering, even while wearing a face mask, may not be enough to protect against the virus that's killed nearly 105,000 people in the U.S.
The research showed hand washing further reduced the chance of spread.
"Hand hygiene is paramount," Kraft said. "If you've touched something that you didn't clean yourself, that thing is likely dirty. Your hands need to be clean before you touch your face."
"It's not rocket science. If we use hand sanitizer, and we cover our nose and mouth, that's going to help mitigate some of this transmission," Kraft said.
"Is it perfect? No. Is it better than nothing? Yes."