According to The Washington Post, the CDC investigated 1,600 people who traveled by air who were at risk of spreading SARS-CoV-2 and concluded that almost 11,000 people could have been exposed.
The CDC didn't immediately respond to a request for comment.
The CDC's original update flew below the radar over the weekend, drowned out by the news about Justice Ruth Bader Ginsburg's passing and the ensuing political drama.
Joseph Allen, a professor at the Harvard T.H. Chan School of Public Health and director of the school's Healthy Buildings Program, said on Twitter that the change by the CDC was a "key win" in a battle experts have been fighting since February to get aerosol transmission recognized.
CNN reported that the update to the page was made on Friday. Until now, he said, agency scientists have said that the virus is transmitted through the air when droplets shoot out of one person's mouth or nose in the form of projectiles, directly infecting another person.
This is the same language it posted months ago.
-Eric Feigl-Ding, Federation of American ScientistsOn Friday, the CDC quietly posted new guidelines stating that the coronavirus can be transmitted "through respiratory droplets or small particles, such as those in aerosols, produced when an infected person coughs, sneezes, sings, talks, or breathes".
COVID-19 is thought to spread mainly through close contact from person to person, including between people who are physically near each other (within about 6 feet).
The CDC warned anyone within 6-feet could be exposed if the droplets "land in the mouths or noses" or are "inhaled into the lungs".
In interviews, CDC officials have also acknowledged growing evidence that the virus can in some cases also spread via even smaller, aerosolized particles or droplets that spread over a wider area.
The health agency had said that COVID-19 could spread through airborne particles that can remain suspended in the air and travel beyond six feet.
"In general, indoor environments without good ventilation increase this risk", the guidance read.
The now-withdrawn guidance, posted on the agency's website on Friday, recommended people use air purifiers to reduce airborne germs indoors to limit the spread of the disease. Some viruses are highly contagious, like measles, while other viruses do not spread as easily. That language has now been removed.
The updated guidance reads: "Due to the significance of asymptomatic and pre-symptomatic transmission, this guidance further reinforces the need to test asymptomatic persons, including close contacts of a person with documented SARS-CoV-2 infection".
President Trump has pushed to change information released by the CDC to be in line with his campaign messaging.
A controversial earlier update was not written by CDC scientists and posted online before it had undergone the normal scientific review process, two sources confirmed to CNN last week.