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Wearing a mask in public has now become part of our daily routine.
Many communities across the country mandate that face masks be worn inside public buildings and even outside if social distancing isn’t possible. Because people can spread the virus even before they have COVID-19 symptoms, having everyone wear masks can prevent asymptomatic people from spreading the virus to others.
Now, a new study suggests that universal masking may also reduce the amount of virus in the air—potentially leading to milder or even asymptomatic infections. Researchers say that if everyone wears masks, these reduced exposures to the virus could lead to greater community-level immunity and slow the spread of COVID-19 until an effective vaccine is developed.
In this Q&A, infectious disease epidemiologist Chris Beyrer, MD, MPH ’91, Desmond M. Tutu Professor of Public Health and Human Rights at the Johns Hopkins Bloomberg School of Public Health and an author of the study, explains the implications of widespread masking.
You can’t purposely expose a person to the coronavirus and see how well a mask protects them—so how can scientists learn about the protection masks provide?
We have animal models that we can use to study this. Most have been done with hamsters separated by mask-like partitions. Uninfected hamsters separated from infected ones by these partitions were less likely to get infected. If they did get infected, they didn’t get as sick as the already infected ones on the other side.
We have epidemiologic data from cruise ships, which also showed that even though many people on cruise ships have gotten COVID-19, since they are quite closed environments, the rate of mask-wearing made a very big difference in how many people who got COVID-19 got much milder infections. In the case of a ship in Argentina, where mask wearing was mandatory for passengers and the staff had N95 masks, more than 85% of people who got COVID-19 had asymptomatic infections. In the general population only about 40% of people have this mild form of COVID-19. This suggests mask wearing really made a difference in health outcomes.
What’s a “viral inoculum” and how does it play a role in the severity of disease?
The amount of virus (actually virus particles) in any exposure is known as the inoculum. We have known for more than 50 years that lower inoculums of other viruses, including flu, lead to milder illnesses. Since this is a basic principle in virology, it likely holds true for COVID-19.
Does the type of mask matter?
Yes, masks vary in materials, in fit, and also in how well they are used. Most cloth masks, and many handmade face coverings, like bandanas or scarves, do allow some virus particles to enter or to be expelled. But even a partially effective mask, if it reduces the inoculum, could be very beneficial in reducing the severity of disease after an exposure.
This study says it might actually be beneficial for everyone to get lower-dosage exposure from asymptomatic or mild cases as it'd accelerate community-level immunity. What are your thoughts on this?
If more people in a population have exposure, asymptomatic or very mild illness, and are protected from re-infection, then there could be real benefit to decreasing the number of susceptible people in that population. So, mask wearing could play a role in reducing new infections through this mechanism.
Jon Eichberger is a communications associate in the Department of Epidemiology at the Bloomberg School.
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