The transmission of the coronavirus can occur through exposure to respiratory fluids from more than six feet away, the US Centers for Disease Control and Prevention (CDC) said in its updated guidelines published on Friday.
In the updated guideline, the CDC said that exposure occurs when respiratory droplets and aerosol particles containing the virus are inhaled or come directly in contact with the eyes, nose, or mouth.
"People release respiratory fluids during exhalation (e.g., quiet breathing, speaking, singing, exercise, coughing, sneezing) in the form of droplets across a spectrum of sizes. These droplets carry virus and transmit infection," the CDC said.
The agency had previously said the virus spreads "mainly through close contact from person to person" and not through airborne transmission.
It added that increasing distance from a source does not necessarily mean that a person cannot be infected through inhalation of aerosol virus particles.
"Although infections through inhalation at distances greater than six feet from an infectious source are less likely than at closer distances, the phenomenon has been repeatedly documented under certain preventable circumstances," the CDC said.
"These transmission events have involved the presence of an infectious person exhaling virus indoors for an extended time (more than 15 minutes and in some cases hours) leading to virus concentrations in the air space sufficient to transmit infections to people more than six feet away, and in some cases to people who have passed through that space soon after the infectious person left."
The agency added that available evidence continues to demonstrate that existing recommendations such as observing physical distancing, use of well-fitting masks, adequate ventilation, and avoidance of crowded indoor spaces to prevent coronavirus transmission remain effective.
"These methods will reduce transmission both from inhalation of virus and deposition of virus on exposed mucous membranes."
As of May 10, more than 32.7 million people have contracted COVID-19 in the United States, according to the data from Johns Hopkins University.