For the third time in less than a month, the Centers for Disease Control and Prevention has altered its guidance on how Covid-19 spreads. The agency said Monday that airborne transmission is possible, but that it's not the most common way the virus travels from person to person — a position that was published and then removed from its website in September.
The CDC updated its page on the spread of virus Monday to say that "some infections can be spread by exposure to virus in small droplets and particles that can linger in the air for minutes to hours."
Those small droplets and particles in turn may be able to infect people who are farther than 6 feet away "from the person who is infected or after that person has left the space."
In September, the agency quietly changed its website to say that the coronavirus could spread through aerosols, which are tiny particles that can float in the air. But three days later, the language was removed; the CDC said at the time that it was "draft guidance" that had been posted "in error."
On Monday, the CDC issued a statement on the latest set of transmission guidelines, acknowledging "the existence of some published reports showing limited, uncommon circumstances where people with Covid-19 infected others who were more than 6 feet away or shortly after the Covid-19-positive person left an area."
"In these instances," the statement said, "transmission occurred in poorly ventilated and enclosed spaces that often involved activities that caused heavier breathing, like singing or exercise."
Covid-19 "spreads very easily from person to person," the CDC website says, most commonly within 6 feet of another person, especially when an infected person coughs, sneezes, sings, talks or even breathes.
The CDC also said that it's possible for a person to become infected by touching a contaminated surface, and then touching their own mouth, eyes or nose, but that it's a much less common method of transmission.
Joseph Allen, an associate professor in the department of environmental health at the Harvard T.H. Chan School of Public Health, said that it's "about time" the CDC made these changes regarding airborne transmission.
"This is exactly what we've been saying for many months ... that viable infectious virus can travel beyond six feet," Allen said. "If you're indoors with someone who's shedding virus, and there's low ventilation, well, the viral particles can build up in the room. And then the six feet is not so protective."
"The term airborne is not to be feared, it just means we have to take some additional precautions," he said. Those include increasing ventilation and air filtration indoors, as well as continuing to wear a mask, wash your hands, and social distance.