The CDC guidance comes weeks after the agency issued, and later removed, a similar warning, sparking debate about how the virus spreads.
In Monday’s guidance, the CDC said there was evidence that people with COVID-19 possibly infected other people who were more than 6 feet away, inside poorly ventilated confined spaces.
In such circumstances, the CDC said scientists believe that the number of smaller infectious droplets and particles, or aerosols, produced by people with COVID-19 becomes concentrated enough to spread the virus.
The CDC has long warned of transmission via tiny droplets that shoot through the air and generally fall to the ground, resulting in the six foot social distancing rule. The aerosol droplets are much smaller still and can remain suspended in the air, like smoke.
While the CDC emphasizes that transmission by close contact is more common than through the air, a group of American scientists warned in an unrelated open letter published in the medical journal Science on Monday that aerosols that linger in the air could be a major source of COVID-19 transmission. (https://bit.ly/34pSPbH)
“The reality is that airborne transmission is the primary way that transmission occurs over short distances with prolonged contact,” the researchers said at a news conference.
Viruses in aerosols can linger in the air for seconds to hours, travel more than six feet, and accumulate in poorly ventilated indoor air, leading to over-propagation events, the researchers said.
Since people with COVID-19 release thousands of virus-laden aerosols and far fewer droplets while breathing and talking, scientists said the focus should be on protection against airborne transmission.
They also said that public health officials must clearly differentiate between droplets expelled by coughing or sneezing and aerosols that can carry the virus greater distances.
Public health officials should highlight the importance of moving outdoor activities and improving indoor air, along with mask wear and social distancing, the letter said.
(Reporting by Vishwadha Chander in Bengaluru; edited by Shinjini Ganguli)
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