The virus that causes COVID-19 spreads in the air — and likely beyond 6 feet.

A group of research scientists and physicians from across the country want to ensure that the public understands what this means and how to prevent transmission of SARS-Cov-2.

The six-member group, which includes Virginia Tech professor Linsey Marr, an expert on the airborne transmission of viruses, urges stronger public health guidance in a letter published Oct. 5 in Science, a journal of the American Association for the Advancement of Science. The group also is calling on the science community to clarify the differences between aerosols and droplets and how exactly they move in certain spaces.

Similarly on Monday, the Centers for Disease Control and Prevention added information to its website indicating that the virus may be spread through the air and while indoors, it may spread beyond a 6-foot distance.  

“The protections that we must use to prevent exposure depend on the way that we understand how the virus spreads,” said Melissa McDiarmid, a member of the research group and professor and head of Occupational & Environmental Medicine at the University of Maryland School of Medicine, during a virtual press conference on Oct. 5.  “If we are not of one voice about this, our preventive efforts will be muddied.”

The letter defines aerosols and droplets. Viruses in aerosols, smaller than 100 microns, can remain suspended in the air from seconds to hours and can be inhaled. Meanwhile, viruses in droplets typically fall to the ground in seconds, within 2 meters of the source, and can be sprayed like little cannonballs onto nearby people, according to the letter.

Droplets have a limited travel range, so physical distancing reduces exposure to them. But aerosols carrying an infectious virus can travel beyond a 2-meter range and accumulate in poorly ventilated spaces.

Given this information, the standard 6-foot distance guidelines to prevent COVID-19 transmission do not necessarily keep aerosols from spreading, said Kimberly Prather, who is leading the group and is director of the Center for Aerosol Impacts on Chemistry of the Environment, which is based at Scripps Institution of Oceanography at the University of California San Diego.

“Aerosols will go beyond 6 feet, and they can build up in a room,” Prather said. “If you are indoors, you are all sharing the air in that room.”

Also, definitions of close contact can be misleading in the case of the coronavirus, said Marr, who is the Charles P. Lunsford Professor of Civil and Environmental Engineering at Virginia Tech.

“It is suggested that transmission is happening by contact or by droplets landing on you, but really in these close situations, there is short range airborne transmission that is probably dominant,” she said.

The group's letter encourages people to wear face coverings indoors at all times and to ensure that spaces are well-ventilated. Also, the scientists urge people to move as many activities as possible outdoors.

“This concept of ventilation is just so important,” Prather said. “In some places that’s just a matter of opening the door and opening the window. Just having clear air is really the best thing you can do.”

To evaluate a space’s ventilation, Marr said she often imagines what it would be like if someone is smoking a cigarette in the same area.

“What if all of the people in that situation are smoking?” she said. “Are you going to be exposed? Will you breathe a lot of cigarette smoke? If yes, you need to do something to change the situation.”

The length of time for inhaling aerosols also is problematic. Passing by someone on the street is not as risky as being indoors with others for long periods of time, Prather said.

“The riskiest places are indoor locations with poor ventilation where people are talking, yelling, and [wearing] no masks,” she said. “That’s where we are seeing a huge amount of the spread.”

Wearing a mask or face covering is critical and even can blunt the seriousness of the virus exposure, said Robert Schooley, a professor of medicine at the University of California San Diego.

“There is evidence that the severity of the illness is a function of how much virus you are exposed to,” he said during the news conference. “Wearing a mask will decrease the likelihood that you will end up with a serious case of the disease. Some things we can’t control, but we can control how much virus we are exposed to.”

By Jenny Kincaid Boone