What Do We Know about Airborne Transmission of the Coronavirus?

Last week, the Centers for Disease Control and Prevention posted—then removed—updated guidelines about airborne transmission of SARS-CoV-2, the coronavirus that causes COVID-19. These guidelines indicated that there was good evidence that the virus can travel further than six feet through the air (the current presumed safe physical distance), especially in indoor settings without good ventilation.

When we breathe, talk, sing, or cough, we produce respiratory particles of a variety of sizes. If a particle is five micrometers or larger, it’s considered a droplet. If it’s smaller than that, it’s an aerosol. The larger, heavier droplets that we spew will fall to the ground first—usually within about six feet or less. Smaller particles can travel farther or hang in the air like smoke. “When the CDC and the WHO say airborne, they almost always mean aerosolized transmission,” says Samuel Scarpino, an assistant professor at Northeastern and head of the Emergent Epidemics Lab.

We know this coronavirus can be spread through contact with larger droplets. The question is, can these smaller particles, known as aerosols, also transmit the virus?

“We have an increasingly large body of anecdotal evidence that is all pointing in the same direction, which is that the virus can be transmitted via aerosol,” Scarpino says.

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