The Centers for Disease Control and Prevention (CDC) warned in a document published Friday of "repeatedly documented" instances of coronavirus spreading through the air to people more than 6 feet away under certain conditions.
The new document explaining the latest understanding of how the virus spreads is part of a shifting emphasis towards airborne transmission of the virus.
"Transmission of SARS-CoV-2 from inhalation of virus in the air farther than six feet from an infectious source can occur," the new document says in large letters, while noting it is "less likely than at closer distances."
The risk of this kind of spread is highest indoors in places with "inadequate ventilation," when people are shouting or singing, or when people are exposed for long periods of time, the CDC said.
Some experts have been pushing the CDC for months to place a greater emphasis on airborne transmission and the need to improve ventilation, even with something as simple as opening the window in a room. Experts have also long said that outdoors is far safer than indoors.
The CDC acknowledged in October that the virus can spread through airborne transmission, but there has since been a growing emphasis on that method of transmission.
The guidance also places an emphasis on transmission through "breathing in air when close to an infected person." The CDC has also deemphasized the likelihood of contaminated surfaces to spread the virus.
The agency emphasized that while it is updating its understanding of how the virus spreads, the same methods for keeping safe still apply. Wearing a mask, distancing from others, avoiding crowded indoor areas and allowing adequate ventilation are recommended.
Linsey Marr, an expert on airborne transmission at Virginia Tech, welcomed the CDC update, but said it could go further, noting the CDC still says it is "uncommon" for airborne transmission to occur when people are greater than six feet apart.
"This can easily happen with indoors if poorly ventilated and no masks," she wrote on Twitter.
They're calling this uncommon because they aren't looking for it. Their guidelines limit contact tracing to people within 6 feet for more than 15 minutes. Yet they say splash & spray transmission is common. Where's the evidence? /2— Linsey Marr (@linseymarr) May 7, 2021