The principle carrier of Covid-19 is through very fine aerosolised particles released during respiration, the US Centers for Disease Control and Prevention has said.
In the new guidelines, the US medical body said the risk of transmission is greatest within three to six feet of an infectious source sine the concentration of these very fine droplets is greatest in this distance.
However, the body has cautioned that the virus could be passed from more than six feet distance.
"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 6 feet away, and in some cases to people who have passed through that space soon after the infectious person left," it said.
Further, these droplets dry rapidly and are small enough that they can remain suspended in the air for minutes to hours, the US body said. "The risk for infection decreases with increasing distance from the source and increasing time after exhalation," it said.