The Science Behind Wearing Masks: Answers From an Infectious Disease Expert

As COVID-19 cases rise across the nation, masks (and requiring citizens to wear them) have become a major point of contention. We speak with Dr. Jeffrey Shaman, a professor of environmental health sciences and an infectious disease modeler at the Columbia University Mailman School of Public Health, about the use of masks and other ways to slow and prevent the transmission of COVID-19.

Amidst a surge of new COVID-19 cases, especially in the South and West, some states, including California, Michigan and partially Ohio, have begun to mandate the use of face coverings in public spaces where social distancing is not feasible.

Dr. Jeffrey Shaman, a professor of environmental health sciences and an infectious disease modeler at Columbia University, says wearing masks could be critical to disrupting and slowing the spread of the virus.

“When a person puts on a mask and forms some barrier. they’re cutting down some of the particles coming out of the mouth and some of the particles that they might receive from somebody else,” he said.

Widespread mask wearing can reduce and prevent the transmission of COVID-19 from asymptomatic and pre-symptomatic individuals who may not even realize that they are infected. A study looking at the prevalence of these cases found that as many as 45% of cases could be asymptomatic. 

“We do not know how the virus is transmitted. We don’t know how any respiratory virus is transmitted. We know how they can be, but we don’t know what the dominant modes are, we don’t know if aerosol is the most important or fomites or if droplets are,” he said.

When someone infected with a respiratory disease coughs or sneezes, the size of the particles can determine whether expelled viruses fall out of the air as droplets or stay suspended as small aerosolized particles. Fomites form when these virus particles settle on surfaces. 

There is growing evidence of aerosol transmission that would make masks even more crucial in transmission prevention, with a group of 239 experts petitioning the WHO to create new guidelines for limiting aerosolized transmission of COVID-19.

A study out of Hong Kong showed that surgical masks are very effective at reducing respiratory shedding of virus in droplets and aerosols. Researchers have also simulated methods of disease prevention and found that 80% mask wearing—meaning if 80% of people wore masks when around others—would be more effective than a lockdown.

“If you’re wearing a mask and you’re not infected, it can prevent those droplets and aerosols from getting to your mouth and nose so there’s benefit,” he said.

The U.S., however, has seen a shortage of surgical masks along with other personal protective equipment (PPE) like N95 respirators, surgical gowns and gloves. The FDA has recommended strategies to conserve existing supplies.

“There also was a mask shortage. So there were also difficulties there. So when it came time to actually get people to wear it in March, we didn’t have enough masks around in this country. We had to reserve them for healthcare workers in frontline workers,” he said.

Early calls to limit mask use in March were due to concerns of a nationwide shortage of PPE; a poll given to health care workers in late May reported that nearly two-third of surveyed health care workers still reported shortages of N95 respirators. 

But that doesn’t mean we shouldn’t be wearing face coverings. The WHO and CDC have encouraged individuals to wear homemade fabric masks to reduce transmission of COVID-19 and studies have shown that household masks are still effective to reduce exhaled particles by 49-86%.

South Korea is one of multiple Asian countries that have successfully controlled rapid spread of COVID-19 through their initial response protocol, including setting up disease tracking infrastructure and widespread use of face masks.

“The experience with SARS and MERS in South Korea really primed them to be aware that there are infectious disease risks of this nature,” Shaman said.

SARS struck many Asian countries in 2003, leading to more than 8,000 cases. In South Korea, there was a small outbreak of MERS in 2015, leading to roughly 200 cases and 40 deaths. While these historical outbreaks were relatively small compared to that of COVID-19, recent memory of these events has caused many East Asian countries’ responses to be markedly different, including swift and extensive wearing of face masks. 

“They have very high compliance rates in [wearing masks] and it’s not a partisan issue,” he said. 

SARS and MERS, however, were fairly regionalized. The last time the world faced a truly global pandemic was during 1918, during which similar public health measures were enforced to reduce contact and prevent disease spread, as evidenced by photographs and documented records. The new COVID-19 virus presents an even greater threat because of its unique nature of being transmittable asymptomatically.

 ”There are a lot of people walking around who may at most have a little sore throat who’re, when they talk or speak, when they sing, if they call, even if they’re breathing, maybe, shedding virus out and they have no idea that they have, so wearing a mask actually can prevent that,” he said.

While the United States has had instances of disease pandemics, the lack of a severe pandemic in recent years has led to a lack of preparedness to address the disease.

“We really haven’t been primed for it and so we are being caught very flat-footed based on the fact that we have no institutional memory of it. Nobody who was alive and dealt with 1918 and remembers it is around anymore,” he said. “So the reality of this, the danger posed by it, is something that’s often dismissed or sidelined.”

With tens of thousands of new cases of COVID-19 still being recorded daily in the U.S. and new understanding about asymptomatic spread, our disease prevention policies and compliance should be progressing, as well.

“It’s because people don’t know that they have the infection. If you know you have been infected, you may be willing to take measures to prevent somebody from catching it from you. You’ll keep your distance. You’ll stay at home. You’ll wear a mask. You won’t go out at all,” he said.

While masks are one of the easiest and most effectives ways to prevent the spread of the virus, there are other ways to reduce the risk of getting or spreading COVID-19, especially in tandem with mask-wearing, like social distancing and limiting mass gatherings.

“The more you get together with other people the more you’re having opportunities to get or give the virus,” Shaman said. “So you want to try to limit it by limiting your exposure to other people right now and keep apart when you’re near them—wear face masks, wash your hands, try to keep rooms ventilated.”

For Shaman, taking into account the science, mask-wearing is beneficial to both yourself and others and is simply a matter of contributing to both personal and communal well-being. 

“The way that it’s been described to me repeatedly is that it’s good for your own health and it’s courteous and good for the people around you,” he said.

While we are consulting experts in the field to get answers to important questions during this crisis, new information and studies come out almost every day and much remains unknown regarding COVID-19. Midstory encourages everyone to follow all public health and safety protocols and exercise extreme caution.


Please enter your comment!
Please enter your name here