The term for spread of a contagious disease from a respiratory droplet that is small enough to float in the air for hours or spread farther than 6 feet. The spread of these droplets may be affected by humidity, air flow and temperature. Research in this area is ongoing.
Deeper dive
There remains controversy among scientists about the primary way SARS-CoV-2, the virus that causes COVID-19, spreads. SARS-CoV-2 reproduces in our upper and lower respiratory tracts, and is emitted via these droplets when we breathe, talk, sing, cough or sneeze. Understanding how much and how far these droplets spread and remain in the air is a key component of controlling the spread of COVID-19.
In March 2022, President Biden’s deputy assistant Alondra Nelson, Ph.D., published a White House blog post stating that the most common way COVID-19 is spread is through airborne particles. The statement diverges from the CDC, which says that COVID-19 spreads in one of three ways, including airborne transmission, especially in enclosed spaces with poor ventilation and from someone who is more than 6 feet away. The other two routes are respiratory droplets and touching an object contaminated by the virus.
This has been a topic of vigorous debate among scientists since the beginning of the pandemic. In July 2020, hundreds of scientists published a paper urging the World Health Organization and other health agencies to recognize the airborne threat of SARS-CoV-2. But for a variety of reasons, including the challenge of developing guidance on ventilation measures, they did not.
Scientists were confident that certain medical procedures, like inserting a tube in an infected person’s trachea, generates droplets that spread in the air. This is called an “aerosol generating procedure.” It is why medical personnel must wear personal protective equipment when caring for someone with COVID-19.
The disagreement was outside the clinical setting. Scientists disagreed about how many droplets an infected person generates and how and where they travel.
It all comes down to the size of these infectious droplets, according to The Atlantic. Bigger droplets may be pulled down to the ground by gravity. Smaller ones might float around. Until the past few months, both the CDC and the World Health Organization said they believed the main route of COVID-19 transmission was respiratory droplets. Bigger respiratory droplets, say 5 to 10 microns in diameter, fall to the ground – on average, within six feet. This is how the six feet social distancing measure came to be. By staying more than six feet away from an infected person, scientists believed a person could protect themselves from becoming infected.
Accumulating evidence over the past two and half years has demonstrated this may not be the case and that some people who stayed more than 6 feet from an infected person could still become infected. The risk of COVID-19 transmission is now considered to be both from respiratory and aerosolized droplets.