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Explainer: How masks can help prevent the spread of COVID-19

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July 24, 2020

Currently, more than half of U.S. states have statewide mask mandates in place to curb the spread of the coronavirus. The governors of Alabama, Arkansas, Colorado, Indiana, Montana and Ohio all announced statewide mandates last week, bringing the total number of states requiring masks to 30. In addition to statewide mandates, some states and cities have placed certain areas under mask orders, as have many churches and businesses. On Monday, Walmart became the largest retailer to require customers at all of its stores in the U.S. to wear masks. 

How do masks prevent the spread of the coronavirus?

Medical researchers have clearly established that viruses, bacteria, and other pathogens can be transmitted when respiratory droplets escape from a person through such actions as breathing, coughing, sneezing, talking, or singing. Surprisingly, the small particles released through breathing, talking, and singing are potentially more infectious than the relatively larger sneeze or cough-generated droplets. Smaller particles persist in the air for longer time periods and can have a larger probability of penetrating further into the respiratory tract of a susceptible individual.

Scientists aren’t sure why, but the amplitude (loudness) of vocalization is directly correlated with the transmission of respiratory particles. Speaking can release about 2–10 times as many particles compared to coughing, while singing can release 6 times more particles than that emitted during normal talking. Research has also found that more particles are released when speech is voiced than whispered.

“A general rule for minimizing the spread of any respiratory virus,” says James Hamblin, a lecturer at Yale School of Public Health, “Whispering is safer than talking. Talking is safer than singing.”

When someone is breathing, speaking, coughing, or singing, only a tiny amount of what is coming out of their mouths is already in aerosol form. Nearly all of what is being emitted is droplets, which can then evaporate and turn into aerosolized particles that are 3- to 5-fold smaller. 

Because masks can block respiratory droplets emitted by the wearer when breathing or talking, they serve as a form of source control, preventing the transmission of the coronavirus that causes COVID-19. Wearing a mask as source control helps to stop this process from occurring, since big droplets dehydrate to smaller aerosol particles that can float for longer in air. 

What type of masks are effective at preventing the spread of the coronavirus?

The effectiveness of masks depends primarily on how well it prevents the transmission of respiratory droplets. 

A study conducted in April used laser light-scattering to sensitively detect droplet emission while speaking. Analysis showed that while significant levels of droplets were expelled

without a mask, virtually no droplets were expelled with a homemade mask consisting of a washcloth attached with two rubber bands around the head. The authors of the study state that “wearing any kind of cloth mouth cover in public by every person, as well as strict adherence to distancing and handwashing, could significantly decrease the transmission rate and thereby contain the pandemic until a vaccine becomes available.”

Multiple studies since then have found that the filtration effects of cloth masks is similar to surgical masks, and that almost any form of cloth masks that covers both the nose and mouth is sufficient to provide a form of source control for respiratory droplets. One exception is masks with valves, such as the N95 masks commonly used in construction to prevent the inhalation of dust. The one-way valves close when the wearer breathes in, but open when the wearer breathes out, allowing unfiltered air and droplets to escape.

If masks are effective, why did U.S. health officials change their guidance on wearing them?

In February and March, at the early stages of the pandemic, many health officials such as Dr. Anthony Fauci and U.S. Surgeon General Dr. Jerome Adams advised the general public not to wear face masks. The primary reason for that guidance was the belief that the virus could only be spread by coughing and sneezing, not by talking and breathing. Additionally, it was not fully known that the virus could be transmitted by people who had not shown symptoms of COVID-19. 

Health officials were also unaware that almost any cloth worn over the face could prevent transmission. At the time, they thought that healthy Americans would deplete the supply of medical masks and there would not be enough for those who were sick or who were caring for the sick.

Is wearing a mask safe, and does everyone need to wear one?

According to the Centers for Disease Control (CDC), children younger than 2 years old, anyone who has trouble breathing, and anyone who is unconscious, incapacitated, or otherwise unable to remove the cloth face covering without assistance should not wear masks. For all other groups, wearing a mask is safe and effective.

Properly worn (i.e., loosely fitted over mouth and nose) cloth masks do not allow the build up of harmful levels of carbon dioxide or cause hypoxia, a condition in which the body or a region of the body is deprived of adequate oxygen supply at the tissue level. Masks are also not harmful to you if you are sick with a cold or allergies (though you’ll want to avoid touching someone else’s mask who has been sick). Most people with mild asthma or well-controlled asthma can also wear a mask.

Elderly people should always wear masks in public since they are more susceptible to COVID-19. However, persons with Alzheimer’s or dementia may have a hard time comprehending why they have to wear a mask.

“There are a few people who are not capable of wearing a mask, but the overwhelming majority of people can wear a mask,” says Dr. Charles Lerner, a member of the Texas Medical Association’s COVID-19 task force. “Severe respiratory failure would be one of them. People who may have had some facial injuries.” Lerner, who specializes in infectious disease, says people with health concerns that prevent them from wearing masks usually can’t even leave the home.

As noted above, the purpose of masks is to prevent the spread of respiratory droplets, which are exponentially larger than oxygen molecules. There is therefore no reason to wear a mask that is so constricting that it would cut off one’s own air supply. Masks primarily prevent someone who may have COVID-19 and not be aware of it from spreading the disease to others. But the masks may also protect the wearer by serving as a barrier and preventing them from breathing in respiratory droplets from infected carriers.

What would be the outcome if more people wore masks?

If more Americans wore masks, the number of new COVID-19 cases might drop so low that churches, schools, and businesses could reopen. 

To understand why this is the case, we need to understand the transmission rate of this coronavirus. The number of cases, on average, an infected person will cause during their infectious period is known as R₀  (pronounced “R naught”). A conservative estimate is that the R₀ of COVID-19 is 2.4, meaning an infected person will spread the virus to 2.4 other people.  If 50% of a given population were to regularly wear masks and the masks were only 50% effective in stopping the transmission of the virus, it would reduce the R₀ of COVID-19 to 1.35.

To put this in perspective, at R₀ of 2.4, 100 cases at the start of a month becomes 31,280 cases by the month’s end. In contrast, at R₀ of 1.35 means 100 cases at the start of a month becomes only 584 cases by the end of the month. As a team of medical researchers have noted, “Such a slowdown in case-load protects healthcare capacity and renders a local epidemic amenable to contact tracing interventions that can eliminate the spread entirely.”

In other words, wearing masks is one of the single most important effective means of stopping the spread of COVID-19. If 95% of Americans wore face masks in public, it could prevent more than 45,000 deaths by Nov. 1, according to the University of Washington’s Institute for Health Metrics and Evaluation.

The “Three W’s to ward off COVID-19” are: wearing a mask, washing your hands, and watching your distance. “But of the three, the most important thing is wearing a mask,” says infectious disease specialist Peter Chin-Hong. 

“You should always wear masks and socially distance,” adds epidemiologist George Rutherford. “I would be hesitant to try to parse it apart. But, yes, I think mask wearing is more important.”

What should Christians think about wearing masks?

As ERLC President Russell Moore recently said,

“I don’t like wearing a mask either—who does? But putting one on every day can remind me that my life is not just about my own preferences. I don’t exist in a computer simulation, but in a community. Even if you don’t accept the scientific consensus on masks (and I do), the principle is still valid. Jesus refused to submit to anything that would cause him to sin or that would deter his mission to the cross. When asked not to heal, he healed. When asked not to preach, he preached. When asked to be quiet in the temple, he caused a ruckus.

“And yet, Jesus willingly accepted all sorts of restrictions and inconveniences for the sake of others. Regarding the temple tax, for instance, Jesus said to Simon Peter: “What do you think Simon? From whom do the kings of the earth take toll or tax, from their sons or from others?” When Peter said from others, Jesus replied, “Then the sons are free.” That was not the end of the matter for him, though. “However, not to give offense to them, go to the sea and cast a hook and take the first fish that comes up, and when you open its mouth you will find a shekel. Take that and give it to them for me and for yourself” (Matt. 17:24-27). And this was a matter that did not—even arguably—jeopardize anyone’s life. How much more so can we endure a momentary burden for the sake of not just vulnerable people but the hospital personnel you are tasked with caring for the sick.”