COVID-19: Face masks vs. the science of transmission

In winter 2019, I took my grandson on a research trip to Japan. When we arrived at Narita International Airport he noticed that practically everyone was wearing a face mask and asked if there was some kind of chemical or biological attack.

After I explained that it was customary to wear them during flu season, he responded with an even more pressing question, “Why don’t we do it in the United States?” 

The role of face masks in confronting COVID-19 came up at the very beginning of the pandemic. Many watched images from China showing most people wearing masks, but here in the U.S. the Centers for Disease Control and Prevention (CDC) shied away from recommending them. Though the CDC did not push mask-wearing, it did advise us to scrub surfaces, maintain 6 feet social distance and to stay home whenever possible. As the airborne nature of the virus became apparent, the CDC began advising face masks in early April 2020. By that time, China, with its mask mandate, was already coming out of the lockdown.

We now know that most of the people got infected by inhaling the airborne virus. Droplets containing the virus are released from the mouth of an infected person. Large droplets fall on surfaces within a few feet, while small droplets stay in the air. During winter months, heating indoor spaces creates dry conditions, making more droplets evaporate before reaching ground. It releases more aerosol virus in the air where it may linger for hours.

The spread of the virus follows the pattern of the airflow created by invisible vortices that are always present in the room due to ventilation, unequal heating, motion of people, etc. Probability of infection depends on the concentration of the virus in the air and the time one spends inhaling the contaminated air. Face masks provide good protection but not 100 percent. 

Hopefully, we will start wearing face masks during flu seasons. They have helped save countless lives from COVID-19 by flattening the curve. They reduced the number of people infected daily below the maximum that the health system could handle. By slowing down the transmission of the virus, we stretched the pandemic in time. This was justified by the necessity to reduce the pressure on hospitals and in the anticipation of the vaccine. What about now?

One cannot contaminate the ocean with a bottle of poison. Concentration of the virus outdoors, away from the source, quickly reduces below dangerous levels. Unless you are spending time face-to-face with a super spreader, the probability of inhaling a critical dose of the virus outdoors — vaccinated or not — must be lower than the probability of having a heart attack from the lack of oxygen due to the mask. Until recently, CDC guidelines were surprisingly restrictive in that respect.

The probability of a fully vaccinated person to become infected or infect others indoors must be lower than having a traffic accident on the way to work. I have not heard of the CDC advising people against driving. Then why are they recommending that “fully vaccinated people engaging in indoor social activities in public settings should continue to wear a well-fitted mask?” Instead of promoting vaccination, which would allow individuals to throw away masks, eat at restaurants, shake hands, kiss each other on the cheek, etc., the CDC likely discouraged some people. Fortunately, this was recognized in the newly updated guidelines.

Our common goal must be herd immunity — when the virus fails to spread because a sufficient fraction of the population, between 70 percent and 75 percent, becomes immune to it. Can we reach herd immunity if 40 percent of the population refuse to get vaccinated? Yes, if doctors allow this 40 percent to get infected and develop natural immunity. They are mostly young people, who will get over it. The alternative is to wear masks all year around forever. Then one day we may learn about the negative effect of face masks on the human respiratory system and mental health.

Eugene M. Chudnovsky is a distinguished professor of Physics at the Graduate School and Lehman College of the City University of New York. He has done research and published articles on the spread of the airborne virus.