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Posted on January 7, 2021 at 3:54 PM

Finally, the Centers for Disease Control and Prevention is working on developing standards for masks to see which ones actually block viruses. In the meantime, though, we should all be acting on what we do know about effectiveness. I cringe when I see a cashier at a grocery store or a delivery person wearing a cloth mask. Why? Because cashiers and delivery people are at high risk of exposure to Covid-19, and cloth masks are substandard masks. Surgical masks (also called medical masks) have a waterproof layer, and are far more effective than cloth masks at preventing illness. Sure, any mask will have some effect, but cloth masks are less than half as effective as surgical masks at protecting the person wearing the mask.

People seem to be aware that N95 masks are better than cloth masks, but why aren’t public health people telling people to wear the masks that we know work better than cloth? Wearing a surgical mask or a N95 mask is the virus prevention measure with the most evidence of benefit. N95 masks may be more effective in high-risk medical environments (although quality varies).  In most circumstances, however, surgical masks are not far behind N-95s in terms of effectiveness. Systematic reviews of numerous studies have found that in real-life settings, surgical masks are about as effective as N 95 masks at reducing the risk of acquiring respiratory illnesses, including flu; another systematic review found similar results.

In contrast, a recent Danish study that specifically looked at Covid-19 transmission found that mask-wearers and people who don’t wear masks had similar risk of viral infection. This study has been both vilified and celebrated, depending on which side of the mask debate you are on, but both the attackers and celebrants misinterpret the study. The Danish study was performed during a time when social distancing and other preventive measures were widespread, and both mask use and transmission rates were low. Under those circumstances, mask use did not reduce transmission to mask-wearers by half; the study was not designed to detect, say, a 40% reduction in risk. The Danish study is entirely consistent with the concept that widespread masking is vitally important to reducing risks in populations.

A recent study by the Centers for Disease Control and Prevention adds to this evidence.

On July 3, 2020, an executive order from the governor of Kansas mandated the use of face coverings in public spaces. A law passed only weeks earlier allowed counties to adopt less stringent public health measures than required by the state. Two dozen counties took advantage of the new law to ignore the governor’s executive order, while 81 counties, comprising about two-thirds of the state’s population, complied with the order to mask up.

Five weeks later, new daily cases of COVID-19 had decreased every day in the counties that complied with a mask mandate and increased every day among counties without a mask mandate. This was particularly stunning because rates of Covid-19 were higher to start with in the counties that chose to follow the mask mandate. Some counties had already restricted the size of gatherings and the number of people in restaurants, but an additional analysis found that counties that just went with the mask mandate experienced similar decreases to counties that adopted a multimodal approach.

Epidemiologists call this sort of experience a natural experiment. Assigning people to use or avoid masks during a pandemic of a dangerous infectious disease would be  unethical, but Kansas has given us a gift of data that allows researchers to compare mandated mask use versus free choice in geographic chunks across a single state. Some people in counties that didn’t mandate masks wore them anyway, making a difference harder to spot. The fact that a significant difference was seen anyway is great evidence that requiring mask use lowers infection rates while laissez-faire I’ll-wear-a-mask-when-I-feel-like-it freestyling does not work. The Kansas study backs up another study that showed a decrease in  rates of Covid-19 cases in Washington, D.C. and 15 states that mandated mask use, compared to states that did not.  

Surgical masks are readily available and cost about 50 cents each. It is urgently important that postal workers, delivery people, cashiers, restaurant workers, factory workers, security guards and anyone whose work involves regular contact with other people should use surgical masks, which are two to three times as effective as cloth masks.

Better yet, apply that to everyone. If you are going to a grocery store, drugstore, gym, place of worship, restaurant or–let’s face it, any place indoors with other people not of your household–  wear a surgical mask.

Wear surgical masks, not cloth masks, whenever you are inside with people outside your home, and change them when they are damp. Moisture reduces efficacy. Also, get ASTM-certified Level 2 or Level 3 masks; The FDA has a list of acceptable surgical and N-95 masks on its website. Save the cute cloth masks for outdoors, where the risk of transmission is very low. A study of 7,324 Covid cases in China found only one outdoor outbreak, involving two people in extended contact.

Because some people with Covid-19 have no symptoms, everyone should consider themselves as potentially infectious. The more layers of material between humans talking to or breathing on each other, the fewer infections we will have. The less shared air between people, the better.

When we all wear masks, infection rates go down.

Adriane Fugh-Berman, MD, is a professor of pharmacology and physiology at Georgetown University Medical Center and director of  PharmedOut, a Georgetown University Medical Center project that advances evidence-based prescribing and educates health care professionals about pharmaceutical marketing practices. She is a paid expert witness at the request of plaintiffs in litigation regarding pharmaceutical and medical device marketing practices. Twitter: @Pharmed_Out.

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