The Centers for Disease Control and Prevention (CDC) said Monday that coronavirus can spread through "airborne transmission" to people who are more than 6 feet away under certain conditions.
The update on the agency's website is an important change to the understanding of how the virus spreads, and one that many experts have been pointing to for months.
The new guidance comes after the CDC sparked confusion last month by posting a document online about airborne transmission, only to take it down and say it was still being reviewed.
Now, the agency has finally posted the guidance, which is careful to say that airborne transmission "sometimes" happens but that the virus "most commonly" spreads between people who are within 6 feet of each other.
The danger of airborne transmission beyond 6 feet largely occurs indoors in poorly ventilated space, which is part of the reason why outdoor activities are considered safer.
"CDC continues to believe, based on current science, that people are more likely to become infected the longer and closer they are to a person with COVID-19," the agency said in a statement. "Today’s update acknowledges 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, transmission occurred in poorly ventilated and enclosed spaces that often involved activities that caused heavier breathing, like singing or exercise."
The CDC continues to advise people to avoid spreading the virus by staying six feet away from others, wearing a mask, and washing their hands. To help prevent airborne transmission, which occurs through smaller particles that can linger in the air, the CDC also advises: "Avoid crowded indoor spaces and ensure indoor spaces are properly ventilated by bringing in outdoor air as much as possible. In general, being outdoors and in spaces with good ventilation reduces the risk of exposure to infectious respiratory droplets."
Linsey Marr, a Virginia Tech professor who has long warned of airborne transmission of coronavirus, wrote on Twitter that the document is "an accurate, sorely-needed update acknowledging airborne spread and importance of masks at all times around others and of ventilation. Hooray!"
--Updated at 2:22 p.m.