Vigilant mask wearing might have spared nearly 140 people from catching the coronavirus at a hair salon in Missouri, according to a report published on Tuesday by the Centers for Disease Control and Prevention. In May, the people interacted with two hair stylists with confirmed coronavirus infections, but none ended up showing symptoms of Covid-19.

The team behind the study, which includes members of Missouri’s Springfield-Greene County Health Department, cannot be certain of all the factors that helped avert what might otherwise have been a disastrous outbreak. But policies instructing locals to cover their mouths and noses, put in place by the city of Springfield and by the salon where the stylists worked, Great Clips, appear to have played a substantial role in curbing the spread of disease.

“This really shows the power of face coverings, especially in indoor settings,” said Nadia Abuelezam, an infectious disease epidemiologist at Boston College who wasn’t involved in the study.

The findings reiterate what scientists have been saying for months: Face masks are an essential part of the disease-prevention tool kit, said Juan B. Gutiérrez, a mathematical biologist at the University of Texas at San Antonio who models coronavirus transmission, but wasn’t involved in the study. “If we get that message out to people consistently, we might be able to contain this.”

Both stylists fell ill in mid-May. But they continued to work with clients for about a week after they started to feel symptoms, said Kendra Findley, a researcher at the Springfield-Greene County Health Department and an author on the study.

At the time, Springfield’s businesses had just begun to reopen, and confirmed coronavirus case numbers in the region were extremely low, said Dr. Robin Trotman, an infectious disease physician and an author on the study.

“There were days when we had one or two cases, max,” he said. Such low local prevalence may have been part of the reason that the first stylist chalked her cough and fever up to allergies and kept returning to work, Ms. Findley said. Against recommendations, she returned to her job even while awaiting her coronavirus test results, which she got two days after taking her test.

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The second Great Clips employee fell ill within days of her colleague, though none of the other four stylists on staff ended up feeling unwell. The two sick stylists both eventually tested positive for the coronavirus, after which they were told by the salon to isolate at home.

By that point, however, the pair had come into close contact with 139 clients seeking haircuts, facial hair trimmings and perms — appointments that bring people within inches of each other for 15 to 45 minutes at a time, more than enough time for the virus to travel through the air from person to person.

And perhaps it would have, had it not been for the masks.

In the days after, health officials contact-traced all 139 people exposed to the stylists and asked them to self-quarantine for two weeks. None reported feeling sick during the 14 days that followed their salon appointments. The researchers also offered the clients free diagnostic tests for the coronavirus. Sixty-seven of them accepted; the rest declined. Of those tested, all turned up negative.

“I was shocked,” Ms. Findley said.

Follow-up interviews with 104 of the clients revealed that, in accordance with guidelines, patrons and stylists alike had worn masks for the duration of almost all the encounters documented by the study.

A small handful of clients had donned N95 respirators — devices designed to filter out 95 percent of airborne particles and one of the best forms of protection for health workers. Since the start of the pandemic, N95s have been in dire short supply.

But a majority of people in the study, including the two stylists, opted for cloth coverings or surgical masks — loosefitting accessories that don’t form an airtight seal around the face.

These products are imperfect. But several studies, including some initiated long before the pandemic’s start, have pointed to their usefulness in stymieing the spread of viruses from the wearer’s airway, Julian Tang, a virologist at the University of Leicester who wasn’t involved in the study, said in an email. To a lesser extent, they may also protect a user from incoming spray.

  • Frequently Asked Questions

    Updated July 7, 2020

    • What are the symptoms of coronavirus?

      Common symptoms include fever, a dry cough, fatigue and difficulty breathing or shortness of breath. Some of these symptoms overlap with those of the flu, making detection difficult, but runny noses and stuffy sinuses are less common. The C.D.C. has also added chills, muscle pain, sore throat, headache and a new loss of the sense of taste or smell as symptoms to look out for. Most people fall ill five to seven days after exposure, but symptoms may appear in as few as two days or as many as 14 days.

    • Is it harder to exercise while wearing a mask?

      A commentary published this month on the website of the British Journal of Sports Medicine points out that covering your face during exercise “comes with issues of potential breathing restriction and discomfort” and requires “balancing benefits versus possible adverse events.” Masks do alter exercise, says Cedric X. Bryant, the president and chief science officer of the American Council on Exercise, a nonprofit organization that funds exercise research and certifies fitness professionals. “In my personal experience,” he says, “heart rates are higher at the same relative intensity when you wear a mask.” Some people also could experience lightheadedness during familiar workouts while masked, says Len Kravitz, a professor of exercise science at the University of New Mexico.

    • I’ve heard about a treatment called dexamethasone. Does it work?

      The steroid, dexamethasone, is the first treatment shown to reduce mortality in severely ill patients, according to scientists in Britain. The drug appears to reduce inflammation caused by the immune system, protecting the tissues. In the study, dexamethasone reduced deaths of patients on ventilators by one-third, and deaths of patients on oxygen by one-fifth.

    • What is pandemic paid leave?

      The coronavirus emergency relief package gives many American workers paid leave if they need to take time off because of the virus. It gives qualified workers two weeks of paid sick leave if they are ill, quarantined or seeking diagnosis or preventive care for coronavirus, or if they are caring for sick family members. It gives 12 weeks of paid leave to people caring for children whose schools are closed or whose child care provider is unavailable because of the coronavirus. It is the first time the United States has had widespread federally mandated paid leave, and includes people who don’t typically get such benefits, like part-time and gig economy workers. But the measure excludes at least half of private-sector workers, including those at the country’s largest employers, and gives small employers significant leeway to deny leave.

    • Does asymptomatic transmission of Covid-19 happen?

      So far, the evidence seems to show it does. A widely cited paper published in April suggests that people are most infectious about two days before the onset of coronavirus symptoms and estimated that 44 percent of new infections were a result of transmission from people who were not yet showing symptoms. Recently, a top expert at the World Health Organization stated that transmission of the coronavirus by people who did not have symptoms was “very rare,” but she later walked back that statement.

    • What’s the risk of catching coronavirus from a surface?

      Touching contaminated objects and then infecting ourselves with the germs is not typically how the virus spreads. But it can happen. A number of studies of flu, rhinovirus, coronavirus and other microbes have shown that respiratory illnesses, including the new coronavirus, can spread by touching contaminated surfaces, particularly in places like day care centers, offices and hospitals. But a long chain of events has to happen for the disease to spread that way. The best way to protect yourself from coronavirus — whether it’s surface transmission or close human contact — is still social distancing, washing your hands, not touching your face and wearing masks.

    • How does blood type influence coronavirus?

      A study by European scientists is the first to document a strong statistical link between genetic variations and Covid-19, the illness caused by the coronavirus. Having Type A blood was linked to a 50 percent increase in the likelihood that a patient would need to get oxygen or to go on a ventilator, according to the new study.

    • How can I protect myself while flying?

      If air travel is unavoidable, there are some steps you can take to protect yourself. Most important: Wash your hands often, and stop touching your face. If possible, choose a window seat. A study from Emory University found that during flu season, the safest place to sit on a plane is by a window, as people sitting in window seats had less contact with potentially sick people. Disinfect hard surfaces. When you get to your seat and your hands are clean, use disinfecting wipes to clean the hard surfaces at your seat like the head and arm rest, the seatbelt buckle, the remote, screen, seat back pocket and the tray table. If the seat is hard and nonporous or leather or pleather, you can wipe that down, too. (Using wipes on upholstered seats could lead to a wet seat and spreading of germs rather than killing them.)

    • What should I do if I feel sick?

      If you’ve been exposed to the coronavirus or think you have, and have a fever or symptoms like a cough or difficulty breathing, call a doctor. They should give you advice on whether you should be tested, how to get tested, and how to seek medical treatment without potentially infecting or exposing others.


In this case, even homemade masks that can’t reliably snuff out every virus-laden particle seemed to do the trick — an incredibly encouraging finding, Dr. Gutiérrez said. “Had they not been using those masks, we would have expected a totally different situation,” he said.

Of course, masks alone can’t be considered a foolproof “safety net,” said Saskia Popescu, a hospital epidemiologist and infectious disease expert in Arizona who wasn’t involved in the study. “This is not an excuse to let you go about and do whatever you want, especially if you’re symptomatic.”

Even the patrons of this particular salon may not have gotten off scot-free. For instance, some of the clients who didn’t get tested could have been harboring the virus in the absence of symptoms. And diagnostic tests, which search for coronavirus genetic material, can be faulty. The study also didn’t contact any clients the stylists had interacted with before they felt sick — a period during which the virus can still transmit to others.

Dr. Abuelezam also cautioned that the outcomes of Springfield’s Great Clips incident would not necessarily hold under other circumstances. “This is about short-term exposure, indoors,” she said. “We cannot generalize these results to a situation where people are spending prolonged periods of time indoors together.”

A hint of that may even come from the first stylist’s behaviors: It’s very likely that she inadvertently passed the infection to the second Great Clips employee during several unmasked encounters, Ms. Findley said. (She also may have transmitted the virus to three family members — presumably also while maskless.)

Even with some protection, co-workers who spend much of their day together may have a much harder time minimizing transmission, Dr. Popescu said.

As discussions on exposure continue, she added, “We can’t just focus on employee to client, or patient to health care worker, or teacher to student. We also need to discuss what’s happening between employees.”

Still, “I hope this encourages people to take masks more seriously,” Dr. Abuelezam said. “Clearly, they have a purpose.”