On Monday, September 21, the US Centers for Disease Control and Prevention (CDC) revised its guideline on COVID-19 to remove all mention of small aerosol particles as plausible modes of spreading of the virus. According to a The Hindu report, this revision comes three days after an update on the CDC website that suggested that the viral infection can spread through small aerosol particles in air.

With regards to the older advisory, the CDC has noted in a disclaimer on its website that the “draft version of proposed changes to these recommendations was posted in error to the agency’s official website.” It added that the agency is “currently updating its recommendations regarding airborne transmission of SARS-CoV-2” and will release the revised guidelines once the “process has been completed.”

The older advisory, released on September 18, included breathing and singing as possible activities that propel the transmission of the virus. However, the new guidelines do not mention these activities.

While the earlier guidelines stated that “particles can be inhaled into the nose, mouth, airways and lungs and cause infection. This is thought to be the main way the virus spreads,” the updates advisory indicates that “droplets can land on the mouths or noses of people nearby or possibly inhaled into the lungs.”

A possible reason that has been suggested for the removal of the previously released guidelines is that they posited a certain ambiguity about the various modes of viral transmission. The advisory had stated that inhaling of particles is “thought to be the main way the virus spreads”, which suggested that small particles such as aerosols play a predominant role in viral transmission, thereby reducing the relative importance of the role of respiratory droplets.