The US Centers for Disease Control and Prevention (CDC) said that Covid-19 can spread through virus lingering in the air, sometimes for hours, as it acknowledged concerns voiced by public health experts about the airborne transmission of the virus.
The agency had published similar warning weeks back but took it down after it sparked debate over how the virus spreads.
The CDC has now again revised the guideline which says that evidence that people with Covid-19 possibly infected others who were more than 6 feet away, within enclosed spaces with poor ventilation.
CDC said under such circumstances, scientists believe the amount of infectious smaller droplet and particles, or aerosols, produced by the people with Covid-19 become concentrated enough to spread the virus.
The CDC has warned of transmission through small droplets that shoot through the air and generally fall to the ground, which resulted in the six-feet social distancing rule.
Aerosol droplets are much smaller still and can remain suspended in the air, like smoke.
Meanwhile, a group of US scientists also warned in an open letter published in the medical journal Science on Monday that aerosols lingering in the air could be a major source of novel coronavirus transmission.
"The reality is the airborne transmission is the main way that transmission happens at close range with prolonged contact," the US researchers said.
Viruses in aerosols can remain in the air for seconds to hours, travel more than two meters and accumulate in poorly ventilated indoor air, leading to superspreading events, the scientists said.
Scientists said the focus must be on protecting against airborne transmission since individuals with Covid-19 release thousands of virus-laden aerosols and far fewer droplets while breathing and talking.
They also said public health officials should clearly differentiate between droplets ejected by coughing or sneezing and aerosols that can carry the virus to greater distances.
"Public health officials must highlight the importance of moving activities outdoors and improving indoor air, along with wearing a mask and social distancing," the letter said.
