Decoding the CDC’s Scientific Brief on Airborne Spread of COVID-19

Last week, the CDC issued a much-anticipated brief about SARS-CoV-2, the virus that causes COVID-19, and how it spreads. For several weeks, contact tracing data seemed to suggest that the virus was airborne under certain very specific circumstances. I would like to share what that means from a public health perspective and my recommendations regarding how we, as a society, should respond.

There are three major ways that infectious illnesses spread. The first one is by person-to-person contact or indirect contact with contaminated objects. Pink-eye is a common example of an illness that spreads by contact. One recent study found that, in complete darkness and at a temperature of 68 degrees Fahrenheit, the virus can remain viable on common surfaces for up to 28 days. While it is theoretically possible for COVID to spread in this way and further study is needed, this is not the primary or even the secondary way we have seen COVID spread. This means that you do not need to wipe down your groceries with a bleach wipe as you put them away, as we thought in the early days of the pandemic. Washing your hands frequently, however, is still a great way to limit person-to-person and indirect contact with COVID and other illnesses.  

The second way infectious diseases spread is by respiratory droplets, which are produced when we breathe, speak, sing, cough, and sneeze. The common cold, the flu, and COVID are all spread most commonly by respiratory droplets. The droplets fall out of the air quickly and close to the source, within 6 feet. This is why maintaining 6 feet of social distance and wearing a mask are both great defenses against COVID. If you have the illness, the droplets will be stopped by your mask. Most of the droplets that get through will fall out of the air before they reach the next closest person.

The smaller droplets quickly dry and become particles that can hang in the air for minutes or hours. Depending on the conditions, they can travel through the air far from their source. These two factors—how long the infection stays in the air and how far it can travel—are what defines airborne transmission. Common airborne infections include the chicken pox and measles.

If COVID were primarily airborne, we would have seen much greater numbers of cases earlier in the pandemic. But airborne transmission of COVID can happen under specific circumstances, especially in enclosed spaces with little ventilation and when an infected person is with other over a prolonged time (30 minutes – a few hours).  

“These transmission events appear uncommon and have typically involved the presence of an infectious person producing respiratory droplets for an extended time (from 30 minutes to multiple hours) in an enclosed space,” the report states. “Enough virus was present in the space to cause infections in people who were more than 6 feet away or who passed through that space soon after the infectious person had left.” 

So what does this mean for us? Our current precautions—masking, distancing, and handwashing—are great protection against the spread of COVID by both contact and respiratory droplets. To avoid airborne transmission of COVID, we need to remember a few other important precautions.

• Socialize outside. With ample ventilation outside infectious particles are dispersed quickly and become harmless. Continue to wear your mask and maintain 6 feet apart, even when outside.
• If you must socialize inside, keep the number of people as small as possible, wear masks, keep your distance, open a window, and keep it short, no more than 20 minutes. Doing each of these things will decrease the airborne particles in the room and help keep people safe.

COVID is still a relatively new disease, and there are many things we do not yet know. The confirmation of the possibility of airborne transmission is just one more step in a learning process that is likely to take many years. More information about indirect spread may also become important. What we do know for sure is that taking precautions limits—but doesn’t completely eliminate—the likelihood of catching COVID.

Marie George, MD, FIDSA, of SVMC Infectious Disease, is an infectious disease specialist.