We’ve been getting this question a lot as we head back to campus for the beginning of the fall semester, some of us for the first time in almost 18 months. The MIT community has a vaccination rate of nearly 98 percent, regularly tests everyone who accesses campus, and requires face coverings indoors. But the prevalence of the highly transmissible Delta variant and the increased possibility of breakthrough infections, however uncommon, have many us looking for more specific guidance on choosing an appropriate face covering.
When it comes to cloth masks, the CDC’s recommendations have not changed. They continue to suggest choosing a mask with two or more layers of tightly woven, breathable fabric that fits snuggly, completely covers your nose and mouth, and includes an adjustable nose wire to keep air from leaking out of the top.
However, the results of a recently published, real-world study that provided free masks to more than 178,000 rural villagers in Bangladesh suggest that well-fitted surgical masks may be more effective than similarly well-fitting, multi-layer, cloth face coverings. Although the overall infection rate in the country was low at the time, villages where residents were provided with free masks showed reduced levels of viral spread compared to similar villages where no masks had been distributed. But the protective effect of masks was greater in villages where surgical masks were in use, compared with villages using cloth masks.
New CDC recommendations, issued last week, provide a more nuanced view of mask choice than earlier guidance. The new guidance includes a video tutorial on improving the fit of inexpensive, disposable surgical masks (available to MIT departments, labs, and centers through the online MIT COVID-19 store). It also includes considerations for the use of medical-grade N95 respirators in certain non-healthcare settings, something the agency had previously advised against. When worn correctly, an N95 forms a tight seal on the wearer’s face and blocks out at least 95 percent of small airborne particles.
“Speaking from personal experience,” says Medical Director Cecilia Stuopis, “I can tell you that a properly fitted N95 is very uncomfortable. Even with the Delta variant, an N95 will still be overkill for most people in most situations.” This is especially true, she explains, in an environment like MIT where people are tested regularly, the positive-test rate is low, and the vaccination rate is incredibly high.
“Back in February, when we were beginning to talk about the emergence of new variants and the possible need for higher-filtration masks, very few people were vaccinated,” Stuopis notes. “But now, if you are vaccinated and wearing a well-fitting, multi-layer fabric or surgical mask, you are very likely to be well protected in most situations.”
But when might you need a higher level of protection? “It comes down to individual risk and situational factors,” Stuopis says. “People who are immunocompromised or otherwise more vulnerable due to other medical conditions or age, should exercise additional caution, even if they are vaccinated. You should also take extra precautions if you are a vaccinated individual who has regular close contact with individuals who are vulnerable, including children who are too young to be vaccinated themselves, or if you’re caring for someone who is sick.” The CDC also recommends that people consider additional protection when using public transportation or working at a job that involves interaction with large numbers of the public, especially when public mask use is inconsistent.
When it comes to assessing situational risk, Stuopis advises considering the factors of time and distance. “For example, we’ve documented transmission occurring between masked individuals who were working together in small, poorly ventilated spaces for extended periods of time,” she says. “That’s the type of situation where you’d definitely want a mask with better filtration properties.”
What are some high-filtration options? While N95s are becoming easier to find, counterfeits abound, and other options are readily available. Some experts recommend a KF94, the certified mask used in South Korea. It’s readily available online and relatively inexpensive — about $40 for a pack of 20. It’s made of a nonwoven material, similar to that of the N95, but it has ear loops instead of bands that go around the back of the head, so it won’t fit as snugly. It’s disposable but safe to reuse a few times.
And there are other ways to achieve close to the same filtration results. In a study published in February, researchers tested 10 different types of face coverings for their effectiveness at protecting both the wearer and others. Based on those results and the results of similar studies, the authors recommend two different “maximal protection” options:
- A three-layer mask with an outer layer consisting of a flexible, tightly woven fabric that can conform well to the face and a middle layer consisting of a non-woven high-efficiency filter material such as vacuum-bag material, or
- A cloth mask tightly on top of a surgical mask where the surgical mask acts as a filter, and the cloth mask provides an additional layer of filtration while improving the fit and making both masks perform better than either would on their own.
When either of these face-covering options fit well, the authors say, they should provide an overall filtering efficiency of greater than 90 percent for particles 1 μm and larger, the size of respiratory aerosols considered most important in transmission of SARS-CoV-2, the virus that causes COVID-19.
How do I know if my mask fits well enough? Wondering how much fit matters? Just take a look at this video! To see if your mask (or mask combo) makes the cut, you can perform a modified form of the “user seal check” to test for leakage: Put your hands over the mask, and exhale gently. You shouldn’t feel air coming out the side or up toward your eyes. Then inhale sharply. You should feel the face-piece collapse slightly under the negative pressure. You also want to move your head in different directions to see if the mask stays in place. Read a paragraph or two of text — this article would work — to make sure it doesn’t slide around too much when you talk. And, glasses wearers, if your specs are fogging up, your mask’s fit is not up to snuff.
If the fit of your face covering is wanting, there are several “hacks” you might try to improve both fit and filtration. These include tying the mask’s ear loops and tucking in side pleats (watch a how-to video for surgical-type masks), fastening ear loops behind the head with a claw-type hair clip, or adding a band of nylon hosiery. Another option is a mask brace or mask fitter, which can be purchased inexpensively or fabricated from open-source plans.