The CDC recently updated its coronavirus information to note the coronavirus’s “potential for airborne spread.” This marks some subtle changes in the precautions we should take.
COVID-19 is known to be transmitted mainly by respiratory droplets. This is the reasoning behind physical distancing, since it’s hard for those droplets to travel more than a few feet. Over the past several months, scientists have been debating whether very small droplets—small enough to float through the air—are common enough and infectious enough to be a serious risk.
Regular droplets, the kind that fall to the ground within about six feet, are still thought to be the primary means of transmission. But if aerosols can also be infectious, it means that indoor spaces may be a risk even if you are careful to keep your distance from others.
Here’s what the CDC says about the update:
CDC continues to believe, based on current science, that people are more likely to become infected the longer and closer they are to a person with COVID-19. Today’s update acknowledges the existence of some published reports showing limited, uncommon circumstances where people with COVID-19 infected others who were more than 6 feet away or shortly after the COVID-19-positive person left an area. In these instances, transmission occurred in poorly ventilated and enclosed spaces that often involved activities that caused heavier breathing, like singing or exercise. Such environments and activities may contribute to the buildup of virus-carrying particles.
CDC’s recommendations remain the same based on existing science and after a thorough technical review of the guidance.
If it’s true that small floating droplets are a significant source of transmission, that doesn’t mean that everything we thought we knew is wrong. It just means certain things are even more important than we realized.
Physical distancing is still important
If the coronavirus is commonly transmitted through aerosols, distancing may protect us less than we thought it did. Staying six feet away from somebody means only that we are avoiding those larger respiratory droplets that come from breathing and coughing.
If the smaller droplets can travel and infect people, that means that standing just outside that six-foot radius may still put you at risk. To repeat, this is a change in emphasis, not a complete reversal. Nobody ever said that the six-foot rule was a guarantee. But it may be that the rule provides less protection than we thought.
We should be even more wary of indoor spaces
Outdoors, fresh air circulates and those tiny droplets can float away on the breeze. Indoors, they hang in the air without an obvious escape route.
Ventilating indoor spaces should help. That means opening windows or running an air circulation system, ideally with a filter. But the bigger take-home message is that indoor spaces may be inherently risky. Aerosols could be the reason gatherings with singing and shouting, like church services, may be so problematic.
The need for N95 masks is even more urgent
We already know that medical masks protect better than cloth masks, and N95s protect best of all.
If the virus is transmitted through those tiny droplets, cloth and procedure masks are doing even less than we thought. In that case, we should possibly all be wearing N95s. Unfortunately, supplies are still low. The recommendation to wear “cloth face coverings” (and surgical masks, when available) is based partly on the need to free up those N95s for healthcare workers. That’s still a problem—but the N95 shortage is an even bigger problem if it turns out that our homemade masks aren’t working as well as we thought.
This post was originally published in July 2020 with the headline “What Would It Mean if the Coronavirus Is Airborne?” and was updated in October 2020 to note that the CDC now recognizes airborne transmission.