In an open letter to the World Health Organization July 6, 239 scientists from 32 countries appealed to “the medical community and the relevant national and international bodies” to recognize the potential for airborne spread of COVID-19.
In the letter, authors Lidia Morawska of Queensland University of Technology, and Donald K. Milton of the University of Maryland School of Public Health described a “significant potential for inhalation exposure” at short to medium distances, up to several meters, or room scale.
“Studies by the signatories and other scientists have demonstrated beyond any reasonable doubt,” the authors wrote, “that viruses are released during exhalation, talking, and coughing in microdroplets small enough to remain aloft in air and pose a risk of exposure at distances beyond 1 to 2 m from an infected individual.”
Within three days, the WHO had responded: In the new guidance, released Thursday, July 9, the organization advised that airborne transmission of COVID-19 in crowded, indoor locations with poor ventilation “cannot be ruled out.”
Mode of Transmission of SARS-CoV-2
But didn’t we know this already? Well, yes and no. We knew that COVID-19 predominantly spreads through close contact with an infected person for an extended time. Respiratory droplets expelled by talking, coughing, and sneezing can infect people with the coronavirus, but also other infections like whooping cough, the flu, and the common cold. Infected droplets can soar through the air for up to 2 meters. Hence physical distancing.
But what these scientists are saying is that smaller respiratory droplets could be propelled even farther, and the evidence is building for airborne transmission of SARS-CoV-2. Many scientists are concerned that microscopic droplets of less than 5 microns in diameter become aerosols that can linger in the air for hours and cause infection when people inadvertently inhale the particles.
Airborne spread of infection isn’t new, of course. Tuberculosis, SARS, measles and chickenpox are all airborne. But if SARS-CoV-2 is an airborne pathogen, it increases the risk of infection despite physical distancing. It could also explain superspreader events and how people not in close contact with infected people catch COVID-19.
But, we don’t yet have definitive proof of airborne transmission for SARS-CoV-2.
We still need more evidence for the airborne spread and how much of the virus leads to infection. We also need to know whether tiny respiratory droplets accumulate in aerosol “clouds” as infected people expel them over time, and whether aerosols infect others by inhalation and eye contact.
But even if we don’t have definitive proof, we would be wise to figure this into our current anti- coronavirus practices.
Protecting Against Airborne Infection
Our task is four fold: To stop the production of infectious aerosols, while we also contain them, disperse them or when possible, avoid them altogether.
To stop aerosol production, everyone should wear face masks in public places, even when you think that you’re healthy. Covering your mouth and nose prevents short- and long-range spreading through talking, sneezing, and coughing, but also when laughing, singing, yelling and heavy breathing during exercise.
To contain aerosols, people need to self-quarantine when they have COVID-19 symptoms, were in contact with some who was infected or have tested positive. When you’re sick, just stay away.
To disperse the aerosols, think fresh, ventilated and filtered air. Air disperses respiratory droplets and aerosols, so being outdoors will reduce airborne transmission. But it is not risk-free. Infectious aerosols are like clouds of cigarette smoke from a nearby smoker. Even outdoors, you can still smell smoke if the wind blows it in your direction. When the colder weather arrives, and we spend more time indoors, we need to disperse aerosols with adequate ventilation systems that continuously refresh the area with air from the outdoors or when possible open windows and doors, use fans, and air purifiers or air filters.
To avoid aerosols altogether, steer clear of crowded spaces where people congregate for prolonged periods like in bars, restaurants, offices, schools, choir practice, gyms, fitness classes and places of worship. All, of course, our favorite places. And if you need to be there, remember to physically distance as much as you can.
Blowin’ in the Wind
We’re learning new things about COVID-19 every day. We already know that mask-wearing, hand washing, social distancing, self-quarantine and isolation helps reduce the spread of SARS-CoV-2. Here are a few things to consider if coronavirus is indeed airborne and can be unwittingly inhaled, especially for those of us who are at high risk of becoming seriously ill with COVID-19:
Take comfort from other people wearing masks and keeping their distance from you.
Avoid crowds and hanging out with other people in poorly ventilated indoor areas for long periods.
Avoid long bus and car trips and of course the airlines. On the train, it’s easier to keep your distance. A private sleeper cabin is ideal.
Wear an N95 mask or hybrid mask made with occlusive cotton and electrostatic fabrics that fits snugly over your nose and mouth and add protective eyewear like goggles.
Take advantage of the summer weather and enjoy being outdoors.