By Daniel Politi

The Centers for Disease Control and Prevention is finally acknowledging something that health experts have been saying for a while now: COVID-19 spreads through the air and can be inhaled by someone who is more than six feet away. The CDC said in a document published Friday that it has “repeatedly documented” instances of the virus spreading through the air to people who were more than six feet away “under certain preventable circumstances.” This marks a change for the agency that previously said most infections took place through “close contact, not airborne transmission.”

“COVID-19 spreads when an infected person breathes out droplets and very small particles that contain the virus. These droplets and particles can be breathed in by other people or land on their eyes, noses, or mouth. In some circumstances, they may contaminate surfaces they touch. People who are closer than 6 feet from the infected person are most likely to get infected,” the CDC now says on its website.

This comes after months of infectious disease experts warning that the CDC and World Health Organization were focusing too much on the risk of picking COVID-19 from surfaces and emphasizing that “close contact” was needed for infection. That was despite increasing evidence that tiny virus particles could remain suspended in the air even after the infected person left a location. “C.D.C. has now caught up to the latest scientific evidence, and they’ve gotten rid of some old problematic terms and thinking about how transmission occurs,” said Linsey Marr, an aerosol expert at Virginia Tech.

Despite the change, some aerosol experts continue to say the CDC hasn’t gone far enough because it continues to say that transmission from far away is “uncommon,” which Marr said was “misleading and potentially harmful” because “if you’re in a poorly ventilated environment, virus is going to build up in the air, and everyone who’s in that room is going to be exposed.” The CDC’s wording “will lead people to continue to think that maintaining distance is sufficient to prevent transmission,” reads an open letter signed by seven experts, including Marr. “We know that transmission at distances beyond 6 feet occurs because of superspreader events, careful studies of smaller outbreaks, and the physics of aerosols. It can easily happen indoors in a poorly ventilated environment, when people are not wearing masks.”

The change in wording has important implications and illustrates how good ventilation in indoor spaces is key to prevent transmission of the virus and people can stop worrying about cleaning surfaces so much. But the basics remain the same. “Although how we understand transmission occurs has shifted, the ways to prevent infection with this virus have not,” notes the CDC. “All prevention measures that CDC recommends remain effective for these forms of transmission.”

In an opinion piece, Zeynep Tufekci details how things could have been different if the WHO and CDC had acknowledged this earlier in the pandemic:

If the importance of aerosol transmission had been accepted early, we would have been told from the beginning that it was much safer outdoors, where these small particles disperse more easily, as long as you avoid close, prolonged contact with others. We would have tried to make sure indoor spaces were well ventilated, with air filtered as necessary. Instead of blanket rules on gatherings, we would have targeted conditions that can produce superspreading events: people in poorly ventilated indoor spaces, especially if engaged over time in activities that increase aerosol production, like shouting and singing. We would have started using masks more quickly, and we would have paid more attention to their fit, too. And we would have been less obsessed with cleaning surfaces.

Our mitigations would have been much more effective, sparing us a great deal of suffering and anxiety.