Masks are a key tool in the fight against COVID-19, but they also pose some problems.
Infectious diseases physician Sonali Advani, MBBS, MPH, discovered both benefits and challenges of masking early in the pandemic. “The burden of employee furloughs and contact tracing [due to COVID-19 exposure] in hospitals was increasing so much that we needed to implement universal masking,” she said. “All employees, clinical employees or nonclinical employees—they could be the person preparing our food or the employee who is cleaning—everybody in the hospital is wearing a mask at all times.”
Dr. Advani believes that the masking improved infection control at Duke University Health System in Durham, North Carolina, where she is an assistant professor and the associate medical director of the Duke Infection Control Outreach Network. “We started to see a decline in asymptomatic transmission. But what we realized is we were getting most of our masks from China and our supply chain was really impacted. So most of our community hospitals do not have enough surgical masks for universal masking,” said Dr. Advani.
Even if a hospital has enough masks, there are additional concerns raised by universal masking. “You have to make sure that people don't self-contaminate themselves by touching their mask,” she said.
In addition, there are associated communication challenges, since masks make speech unintelligible for those who read lips and can also cause problems for others. “When I'm on a call with someone and I have a mask on, they can't always understand what I'm saying,” said Dr. Advani.
Although these challenges became initially apparent in hospitals, the expansion of masking into outpatient practice and communities has made the related problems universal as well. The good news is that there may be a simple, inexpensive way to alleviate some of these issues. “Face shields have the potential to overcome some of the major drawbacks of facemasks,” wrote Dr. Advani and colleagues in a commentary on universal masking published by Infection Control & Hospital Epidemiology on April 29.
Face shields in action
The authors of that paper will get no argument from Michael Edmond, MD, FACP, a professor of infectious diseases and chief quality officer at the University of Iowa Hospitals and Clinics in Iowa City.
He and his colleagues have advocated for face shields since early in the pandemic, promoting the concept in tweets, blogs, and an April 29 JAMA Viewpoint, as well as putting it into action on the ground.
“At our hospital at the University of Iowa, we have every employee in face shields. That includes both the employees that interact with patients, as well as people that have no patient interaction at all,” said Dr. Edmond. “All of our administrators are in face shields . . . and we even require people that are coming into the hospital to do work—various vendors, construction people—to wear them.”
What a person should wear under a face shield varies by setting and situation, the experts noted. “Depending on the clinical situation, at a minimum the people that are seeing patients have on a medical-grade mask underneath the face shield. If they're involved in some kind of aerosol-generating procedure, then they wear N95s under the face shield,” said Dr. Edmond.
Dr. Advani agreed. “In the hospital setting, we don't know enough where I can say that you can just wear the face shield by itself. Everything that I've seen, in the hospital or in a clinic, we do have to combine it with a mask of some sort,” she said, noting that these recommendations are more empiric than research-based. “We don't have enough evidence for this. We're just working on data that was available from influenza.”
The effectiveness of face shields for infection control in general has not been the subject of much research.
There is a 2014 study, published by the Journal of Occupational and Environmental Hygiene, in which researchers used a simulator to assess how much protection a face shield would offer a health care worker from a coughing influenza patient. The results showed that a clinician 18 inches from the patient could inhale 0.9% of the initial burst of aerosol from a cough and that wearing a face shield reduced inhalational exposure by 96% in the period immediately after a cough and lowered surface contamination of a respirator by 97%.
“The actual question was could you wear a face shield instead of wearing a respirator for respiratory protection? And we were pretty certain the answer was no, but we really wanted to say this is exactly how much protection you get,” explained lead author William G. Lindsley, PhD, a research biomedical engineer for the CDC in Morgantown, W. Va.
The study also looked at the impact of face shields in the 30 minutes after a cough and found that they blocked large infectious particles from being inhaled but that smaller particles remained airborne longer and could flow around the shield.
“Face shields are great in terms of protecting the face from large visible drops from a splash. Or even if somebody is coughing and sneezing those larger droplets, it keeps it off the face,” said Dr. Lindsley.
The study authors concluded that face shields can serve as an adjunct, rather than a replacement, for respiratory protection. “Also, if you're wearing a respirator, it helps keep the surface of the respirator clean,” Dr. Lindsley added.
That's an important advantage right now, the other experts pointed out. The supply shortages that have forced clinicians to reuse respirators and medical masks during the pandemic have been a major argument for face shields. “That's what got me to start thinking about what kind of options we have that are more durable than these paper masks,” said Dr. Edmond. “You can't wear a paper mask indefinitely. They tear, they get wet, they stop doing what they're designed to do.”
Face shields may delay that inevitable result, and they particularly add protection when shortages are even more dire. “Cloth masks are inferior to surgical masks. But if a hospital is using cloth masks due to shortages of surgical masks, combining it with a face shield will be a better alternative than cloth masks alone,” said Dr. Advani.
This is particularly important in resource-poor countries, where Dr. Advani has family members who are clinicians. “They don't have access to a lot of masks,” she said. “I am scared that they're reusing masks. So I asked them why don't you wear a face shield? Face shields are very easy to clean and reuse. You just basically clean them with a disinfectant wipe.” Dr. Advani is currently working on a project to provide such resources to low- and middle-income countries.
While some arguments for face shield use are situation-specific, touching one's face is a universal habit. “On a Zoom meeting I'll just sort of watch people and see how many times they touch their face. We all do it very frequently,” said Dr. Edmond. “Facial touching is kind of involuntary. You're not thinking about it.”
Masks could potentially increase that subconscious urge, with their potential to cause discomfort. “A lot of times when you wear a mask, you'll notice that you want to touch it,” said Dr. Advani.
But if you act on that impulse while wearing a face shield, you'll definitely notice. “There'll be times where my nose is itching and I go to scratch it and the face shield stops me from doing that,” said Dr. Edmond. “You can't touch your face or it makes it very difficult to do that because you have to actually put your hand underneath the shield to touch your face.”
Both the reduction in facial touching and protection from droplets should help reduce the risk of self-contamination among clinicians wearing a mask or respirator under a face shield, Dr. Edmond believes. “One of the concerns with taking off and putting on masks, reusing them multiple times, are you going to contaminate yourself if the mask itself has become contaminated with droplets from someone else?” he said.
Another advantage is the built-in protection for the eyes. “One nice thing about a face shield is it kind of covers your whole face and probably does a little better job of providing broader coverage than just a pair of safety glasses,” said Dr. Lindsley. “I wear prescription eyeglasses and so it's pretty easy for me to put a face shield over my glasses, but it's a lot more of a hassle to try to put glasses over top of each other.”
In the community
The general public hasn't started wearing safety glasses yet, but many are wearing masks in accordance with CDC recommendations and local regulations. Neither the CDC nor the World Health Organization offers guidance or recommendations on face shields in community settings, and no studies have looked at the effectiveness of face shields alone in preventing community transmission of SARS-CoV-2, so data on this strategy are lacking. [Editor's Note: After this issue went to press, the CDC updated its guidance on cloth face coverings, which now includes a paragraph on face shields. The CDC does not recommend face shields for everyday use or as a replacement for cloth face coverings but notes that some may choose to use a face shield when sustained close contact with other people is expected.]
Based on their experiences during the pandemic, however, Dr. Advani and Dr. Edmond believe face shields in the community could make a big difference in combating COVID-19.
“Could a simple and affordable face shield, if universally adopted, provide enough added protection when added to testing, contact tracing, and hand hygiene to reduce transmissibility below a critical threshold?” Dr. Edmond and colleagues asked in their JAMA Viewpoint.
They noted that face shields in community settings would carry the same benefit of reduced risk of self-contamination, as well as some other potential advantages compared to cloth masks.
“In the nonmedical setting, face shields offer several advantages over face masks, and in my opinion, are likely to be more effective as they provide protection for the wearer, as well as some degree of source control. Cloth masks provide little protection for the wearer,” said Dr. Edmond.
Dr. Advani noted another upside. “Between the two, I think a face shield is more comfortable to wear,” she said. “The best advantage that I find when I wear a face shield in the community is that people can see my face.”
The reusability of face shields might help ease supply issues in both the community and health care settings, the experts noted. “I see a lot of surgical masks used in the community,” said Dr. Advani. “If face shields catch on in the community, we might be able to save those medical-grade masks for hospitals. So it might work out well for everyone.”
That said, face shields are not a perfect solution, she noted. “There's definitely disadvantages with face shields, for example, glare or fogging in some cases,” she said. “There's some poor-quality shields out there.”
Availability of quality face shields was initially a challenge. When the University of Iowa began trying to shield everyone in the hospital at the beginning of the pandemic, they found that medical face shields were sold out. “Most or all of the face shields that we purchased for the hospital were not face shields that were marketed for medical use. They are marketed for people that do metal grinding or woodwork,” said Dr. Edmond. “Those were much more available.”
Even then, the necessary quantity was not immediately in stock. “We placed orders with multiple vendors. And we didn't get them all delivered on one day. It was kind of a staggered process,” he said. “As the face shields were coming into the hospital, we were distributing them to people on a rolling basis until we got everybody covered, and that took probably about two weeks.”
Since that time, manufacturers have newly begun or increased production of face shields, Dr. Edmond said. Factories currently working on face shield development range from giants like Apple, Nike, General Motors, and John Deere to a small company that used to make plastic menus for restaurants, he reported.
“There might not be at this moment enough face shields for every person in the country, but I think that in a relative short period of time, it will happen,” Dr. Edmond said. Those who are reasonably handy have another option. “The thing is you can make it yourself,” he said. “They don't have to be really high tech or anything. The idea is just to have your mouth, your nose, and your eyes covered with a piece of clear plastic so that when you're around other people droplets from that other person can't get in any of those places.”
Dr. Advani cautioned that it's hard to know precisely how well a homemade or nonmedical shield will protect against viral spread, but she thinks it's likely better than the current alternatives. “There's no way to say how good it would be,” she said. “It would be better than nothing. It would be better than a cloth mask alone.”
Her confidence in this public health strategy is best evidenced by her personal advice. “My parents are in India, and manufacturers have started making face shields in India. I have asked my parents to buy a couple of face shields for protection if they need to go out in the community,” she said. “I hope it catches on.”