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This story has been updated. It was originally published on March 12, 2021.

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What a difference a year makes. Prior to March of 2020, if you didn’t work in a hospital setting or on a construction site, it’s unlikely you had ever worn a face mask. Now, we own them by the dozens—a grab bag of KN95s and bandanas, surgical masks, and floral-printed fabric coverings. Such is life during a global pandemic. And as case counts have begun rising again because of the new highly infectious Delta variant, it begs the question: Will these shields be with us for the foreseeable future?

Over the past month, the number of new cases of COVID-19 have increased dramatically in many areas of the country, including states that have areas where a significant percentage of the population remains unvaccinated. 

While the number of Americans getting vaccinated had been increasing throughout the spring, since then it has rapidly leveled off. As of the end of July 2021, only about half (49.4 percent) of all Americans have been fully vaccinated; that’s 60.3 percent of adults in the U.S. 

Back in May, the Centers for Disease Control and Prevention (CDC) had relaxed masking recommendations, stating that for those who are fully vaccinated it was reasonably safe to go unmasked both outdoors and inside. But with the rise in cases and, importantly, the rise in cases driven by the Delta variant, a new and highly infectious version of the coronavirus, the CDC announced new recommendations for mask wearing: For those in areas where case counts are high, masks should be worn; additionally in schools, everyone should resume wearing masks at all times. 

With this shift in guidelines, it’s important to remember that masks are highly effective in preventing infection with COVID-19—and experts say there may be good reasons to keep a few tucked away for future use.

How masks have helped us fight COVID-19—and why we didn’t wear them sooner

Wearing a mask might have been a novelty for Americans to get used to this past year, but their large-scale use isn’t new. Face coverings have been a popular public health measure in East Asia for more than a century. According to MIT historian Emma J. Teng, “[masks seem] to have arisen with the 1918 influenza pandemic, becoming commonplace first in Japan.” But their use accelerated after a 2002 outbreak of another coronavirus known as SARS. Now, they’re commonplace in countries like China and Korea, too—something people wear as a courtesy to others if they feel sick, or even as a defense against environmental pollution.

Perhaps because SARS never made its way to America on a population-scale, face masks never made their way into American popular culture. It didn’t help that early in the COVID-19 pandemic, many public health officials in the US advised against wearing masks. Only on April 3, 2020, did the CDC recommend cloth face masks as a way to protect other people, if not the wearer themselves.

There were many reasons for not recommending universal mask wearing. At least one was scientifically sound: At the time, there was little evidence to definitively say masks could stop COVID-19 transmission, says Monica Gandhi of the University of California, San Francisco, School of Medicine. In fact, most of what we knew at that point came from research on mannequins—not real live humans.

For example, one 2010 study inspired by SARS and swine flu and published in the journal Applied Biosafety, fitted Styrofoam heads with four types of face coverings—a surgical mask, a pre-shaped dust mask, a bandana, and an N95 respirator—and then used a nebulizer machine to spray a saline water solution into the air around them. The study found the N95 masks worked best to stop the spread of aerosols. But scientists had a hard time drawing conclusions about how these masks would function in the real world, where the built environment, weather conditions, and even the way people speak to one another can influence viral spread.

As a result, these laboratory scientists could say certain face masks “do block particles physically,” Gandhi says. “But we didn’t have any trial that could say, ok, this needs to be done in a pandemic.”

Over this past year, though, researchers have rigorously studied the benefits of mask wearing not just for those around a masked individual, but for the person wearing the mask themselves. This research has generated ample evidence—from a range of sources, including mannequin studies, statistical analyses, and real world experience—that masks can reduce the risk of catching and spreading the novel coronavirus.

In May 2020, for example, epidemiologists noted a hair stylist who transmitted COVID-19 among their household, but not to their clients, who they only interacted with while masked. In one December 2020 study in the American Journal of Tropical Medicine and Hygiene, researchers demonstrated that per-capita deaths were significantly reduced in areas with widespread mask use, compared to those without. And surgical masks—at least when used as a partition between parts of an animal enclosure—have been shown to reduce the risk of SARS-CoV-2 transmission among non-human animals like hamsters.

The benefits don’t stop at COVID-19, either. Researchers surmise that this year’s flu season was nearly non-existent at least partly or perhaps fully because of our country’s use of masks and social distancing practices.

[Related: Can we ever hug again?]

How we’ll move forward to prevent COVID-19 and other infectious diseases

If masks are so effective at preventing the transmission of various airborne infections, will they ever disappear completely from our lives?

It’s likely that we will reach a point where every day mask wearing, like face covering requirements in grocery stores and other businesses, isn’t necessary. This collective unmasking is “going to be regional,” Gandhi says.

Other states and cities will follow on their own timelines. Some will wait for “herd immunity,” the point at which enough people are immune to COVID-19 to drastically reduce the chance of community spread (though its unclear when or if herd immunity will happen, especially with new variants, particularly the Delta variant, circulate). But some may continue to require masking even after the bulk of the population is vaccinated.

The reasoning is sound: The virus is likely to bounce back in the fall and winter months. We’ve already started to see this happen, mostly driven by the Delta variant making its way through unvaccinated populations. In years to come, it will probably become an endemic disease, periodically surging again and again like the seasonal flu.

Even at the point when masking is no longer a health requirement, it may remain a social one. A year ago, covering your face and nose before entering a place of business was almost unimaginable. But a year in, this practice feels second nature. And now, given the rise in cases again, it’s harder to predict when or if we can safely leave our masks in the drawer. Even when the risk of COVID-19 slowly drops off, some will see the burden of wearing a mask as outweighed by the bit of extra protection it offers, even among those already vaccinated. After a year of unending anxiety, people may also struggle to accept our new reality; for them, leaving the house without a mask may take some practice. As we transition to this “new normal,” Gandhi says face coverings may simply feel polite.

Further, like everything in science, the research behind mask wearing is ever-evolving. While it’s clear now that layered, well-fitting masks do an excellent job of halting the spread of the novel coronavirus, not all viruses and infectious microorganisms spread in the same way. Some research suggests that masks don’t prevent infection with viruses that cause the common cold as well as they do against contact with SARS-CoV-2. That’s likely because common cold viruses can still spread on surfaces, whereas COVID-19 appears to be primarily airborne. But perhaps a year of masking up and carefully tracking our personal and public health risk has taught Americans that covering our faces when feeling a bit off could curtail future outbreaks.

As the COVID-19 pandemic continues to evolve, it will remain important to listen to public health officials.

“They should peel off recommendations when it’s warranted,” Gandhi says.

No pun intended.

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