What we know and don’t know about masks
New York Daily News,
Admit it: Some facets of our newly-masked world are crazy-making. Where we once embraced, “Hi. How are you?” in our everyday lexicon, we’re now stuck with its tedious cousin, “What did you say?” Steve Jobs, in all his brilliance, couldn’t have predicted this state of affairs when Apple was developing its facial recognition software; my iPhone has no idea who the new masked me is.
So, since we’re constantly being reminded to wear them, let’s ask the loaded question: Do these things really work?
As an emergency physician, I can attest to the value of the medical-grade N95 masks used in hospitals. These are fit-tested to each health-care worker annually, and they’ve been shown to be protective. But the cloth masks, the bandanas, the looped blue cotton fashion statements with gaping holes on the sides — do these really protect us?
Short answer: Though some face covering may be better than none, the evidence of effectiveness for over-the-counter and homemade facial coverings is decidedly mixed. All politics aside, that’s what the science shows.
In a large, randomized study performed in 14 hospitals in 2015, researchers in Vietnam found that the use of cloths masks resulted in significantly higher rates of influenza-like infections than that of medical masks — 13 times higher, in fact. Furthermore, the study showed that the cloth masks blocked particles only 3% of the time. Their poor performance, repeated use, and moisture retention may have contributed to the higher incidences of infection.
What about cloth masks for the general public’s use? In April, two experts on respiratory transmission and infectious diseases performed an extensive review and concluded there is “a lack of scientific evidence” that cloth or surgical masks reduce the risk of COVID-19 transmission among members of the general public who are without symptoms.
Their review included information from the National Institute for Occupational Safety and Health, which examined how well different materials filtered out various particles – what’s known as “filter efficiency.” They found the filter efficiency of t-shirts to be 10%, scarves 10% to 20%, cloth masks 10% to 30%, and towels 40% efficient — and when they got down to the tiny size of aerosolized virus particles like the ones believed to be in play with COVID-19, cloth masks had “near zero efficiency.”
Similarly, Korean researchers after examining more than 40 types of masks, found general masks’ filtration efficiency to be only 38%. They concluded that these offered “little protection” against respiratory aerosols. Finally, another recent study found filtration efficiencies for cloth masks to range from 5% to 95%, observing improved performance when multiple layers were used.
Really, though, filter efficiency doesn’t matter much if you’re wearing a mask that doesn’t fit properly. Your mask needs to fit snugly over your nose and mouth, so air cannot leak around the sides, top, or bottom. If there are gaps, as we see in people walking around with loose masks or bandanas, the filter efficiency can drop by more than half. As for the masks that people wear draped below their chins — “chin guards,” in the words of Gov. Cuomo — they clearly afford no protection.
There are, to be sure, some pro-mask studies. An extensive review published in The Lancet this month found that medical N95 and surgical masks or 12- to 16-layer cotton equivalents — a very different breed than typical cloth masks– were associated with a significant reduction in infection risk. Quality matters. A study published in Health Affairs found that mandated mask use in 15 U.S. states between April 8 and May 15 may have mitigated COVID-19 spread (along with social distancing measures, etc.). And finally, a new study found that mask-wearing countries had lower per-capita mortality than countries without mask policies.
While these latter studies look at policy decisions to assess masks’ efficacy, it can sometimes be difficult to tease out what exactly is causing the benefit. The scientific data on cloth mask use in the community is inconsistent and conflicting. No one has proven yet in a well-done, prospective trial that wearing a mask reduces an individual’s chances of inhaling coronavirus droplets. Furthermore, given that many masks are poor-fitting, made of few layers, worn repeatedly, washed or not washed, and often improperly removed (whereby the user may unknowingly contaminate him or herself with the virus), I suspect the benefit is marginal.
Clearly, they’re not the holy grail, given the new outbreak of coronavirus in Beijing despite stringent mask-wearing amongst its citizens. But when worn properly, masks do offer at least some degree of respiratory protection, especially against larger exhaled droplets. And since we don’t know yet what constitutes an appropriate level of protection against COVID-19, the simple answer is to follow health policy recommendations and continue wearing a mask.
Make sure it fits. Go for multiple layers. And be certain that wearing it doesn’t lure you into a false sense of security where you sidle up close to your buddies. Keep a good distance from others, hang with fewer rather than more friends outdoors, fire up the grill, and enjoy the summer!
And if we can’t hear each other through our masks, this may just be a good time in our country to listen. Siri…it’s me.
