Now, the Centers for Disease Control and Prevention agrees. The CDC recently changed its official guidance to note that aerosols are “thought to be the main way the virus spreads” and to warn that badly ventilated indoor spaces are particularly dangerous.

“There is growing evidence that droplets and airborne particles can remain suspended in the air and be breathed in by others, and travel distances beyond 6 feet (for example, during choir practice, in restaurants, or in fitness classes),” the agency stated. “In general, indoor environments without good ventilation increase this risk.”

While the CDC has not called for any new action to address the airborne threat of a virus that has now killed nearly 200,000 Americans, experts said the change should help to shift policy and public behavior.

“It’s a major change,” Jose-Luis Jimenez, a chemistry professor at the University of Colorado at Boulder who studies how aerosols spread the virus, told The Washington Post. “This is a good thing, if we can reduce transmission because more people understand how it is spreading and know what to do to stop it.”