Scientists Believe COVID-19 Is Airborne—Here’s What That Means

Since COVID-19 cases ramped up in early 2020, the World Health Organization (WHO) has reported that the virus and the U.S. Center for Disease Control and Prevention (CDC) have insisted that the virus spreads primarily in large respiratory droplets transmitted from person to person with coughs and sneezes. (The CDC recently flipped then reverted its stance on this issue.) All the while, doctors have insisted that’s not the whole story behind the virulency of COVID-19. On July 4, 239 scientists in 32 countries wrote an open letter to the WHO demanding that the organization revise its recommendation to consider airborne transmission by which COVID-19 may travel from one person to another through smaller particles suspended in the air.

The open letter, which is set to be published in a scientific journal this week, holds that airborne transmission is a major factor in the pandemic. “Aerosols are tiny droplets or particles that may be kept aloft by ventilation systems, making all those guidelines about staying six feet apart indoors less effective in preventing the spread of COVID-19,” says Jennifer Horney, PhD, professor and founding director of the University of Delaware’s epidemiology department. “Larger respiratory droplets fall to the ground more quickly than aerosols, meaning that being farther away from someone breathing, talking, singing, or eating should be less risky.” Marcus Plescia, MD, MPH, chief medical officer of the Association of State and Territorial Health Officials, adds that the measles is yet another example of a disease spread through aerosolization that’s far more infectious than COVID-19.

All this means is that when a medical professional calls a virus “airborne,” they’re referring to its ability to linger in the air over long periods of time. One example, says Dr. Horney, is the flu. “Seasonal influenza can be transmitted through aerosols, respiratory droplets, or contact with secretions on surfaces,” she says. “Since COVID-19 is still relatively new, we are still improving our understanding of the risks associated with each of these transmission methods. For example, although we know from laboratory simulations that the coronavirus can live on surfaces for hours to days, we now know that person-to-person transmission is much more likely.”

Knowing how the virus travels is important because that’s what will determine how we can and should protect ourselves against it. For example, is it really safe to shop at an outdoor market if you’re wearing a mask? What about eating at a restaurant? Or exercising in the park without a mask? “Airborne transmission impacts recommendations about appropriate personal protective equipment and potentially increases the risk of many indoor activities, even when lower numbers of people are present,” says Dr. Horney. “However, even with potential aerosol spread, coronavirus risk is highest when in prolonged close contact, especially indoors.”

For you, this open letter from some of the world’s brightest medical expert should be a reminder that there’s so much about the virus that’s still not known for sure. And it’s a good time to re-remind yourself to wear a mask, stay at least six feet apart, and look out for your fellow human beings (who needs safe air just as much as you do).

Originally published July 6, 2020; updated September 24, 2020.