A new analysis of 172 studies, funded by the World Health Organization, confirms what scientists have said for months: N95 and other respirator masks are far superior to surgical or cloth masks in protecting essential medical workers against the coronavirus.

The results, published on Monday in The Lancet, make it clear that the W.H.O. and the Centers for Disease Control and Prevention should recommend that essential workers like nurses and emergency responders wear N95 masks, not just surgical masks, experts said.

“It’s been disappointing that both the W.H.O. and the C.D.C. have suggested that surgical masks are adequate, and they’re clearly not,” said David Michaels, a professor at George Washington University who headed the Occupational Safety and Health Administration under President Obama.

“Reliance on surgical masks has no doubt led to many workers being infected,” he said.

N95 masks offered 96 percent protection, the analysis found, while the figure for surgical masks was 77 percent. The findings are particularly important as the United States moves to reopen the economy, Dr. Michaels said.

Workers in health care settings are not the only ones at high risk of coronavirus infection: employees in meatpacking plants and some farms are all also at high risk of coronavirus infection and could benefit from N95 masks, he said.

The W.H.O. has not endorsed universal wearing of masks, although most of its member governments adopted the practice months ago. The organization’s stance has frustrated many public health experts who see masks as a simple, inexpensive and highly effective strategy to help contain the pandemic, especially given that the virus can be transmitted by people who do not know they are ill.

“When there is uncertainty and you don’t know everything about a disease, you have to be precautionary, which means you have to assume the worst and provide the best for health care workers,” said Dr. Raina MacIntyre, an epidemiologist at the University of New South Wales in Sydney, Australia, who wrote a commentary accompanying the paper.

“This kind of denial, what purpose is it serving — except to harm health care workers?” she said.

Previous studies have shown that the universal wearing of masks is effective. If anything, the new study does so based on poorer evidence, said Jeremy Howard, a distinguished research scientist at the University of California, San Francisco, and a co-founder of the global #Masks4All movement.

“This is probably what the W.H.O. needs to change their guidance, even though it shouldn’t be,” Dr. Howard said. “Such is life. It will save lives, so that’s good.”

The C.D.C. initially recommended N95 masks for all health care personnel. Dr. MacIntyre said the agency later downgraded its recommendations because of a shortage of N95 masks and personal protective equipment.

“Guidelines should be based on evidence, not on supplies,” she said. “It’s like telling an army, ‘Oh sorry, we’ve run out of guns, just take these bows and arrows and face the enemy.’”

She noted that N95 masks were inexpensive to produce and that other countries, including Australia, had repurposed existing manufacturing facilities to make the masks.

  • Updated June 1, 2020

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      Exercise researchers and physicians have some blunt advice for those of us aiming to return to regular exercise now: Start slowly and then rev up your workouts, also slowly. American adults tended to be about 12 percent less active after the stay-at-home mandates began in March than they were in January. But there are steps you can take to ease your way back into regular exercise safely. First, “start at no more than 50 percent of the exercise you were doing before Covid,” says Dr. Monica Rho, the chief of musculoskeletal medicine at the Shirley Ryan AbilityLab in Chicago. Thread in some preparatory squats, too, she advises. “When you haven’t been exercising, you lose muscle mass.” Expect some muscle twinges after these preliminary, post-lockdown sessions, especially a day or two later. But sudden or increasing pain during exercise is a clarion call to stop and return home.

    • My state is reopening. Is it safe to go out?

      States are reopening bit by bit. This means that more public spaces are available for use and more and more businesses are being allowed to open again. The federal government is largely leaving the decision up to states, and some state leaders are leaving the decision up to local authorities. Even if you aren’t being told to stay at home, it’s still a good idea to limit trips outside and your interaction with other people.

    • 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.

    • 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.

    • 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.)

    • How many people have lost their jobs due to coronavirus in the U.S.?

      More than 40 million people — the equivalent of 1 in 4 U.S. workers — have filed for unemployment benefits since the pandemic took hold. One in five who were working in February reported losing a job or being furloughed in March or the beginning of April, data from a Federal Reserve survey released on May 14 showed, and that pain was highly concentrated among low earners. Fully 39 percent of former workers living in a household earning $40,000 or less lost work, compared with 13 percent in those making more than $100,000, a Fed official said.

    • Should I wear a mask?

      The C.D.C. has recommended that all Americans wear cloth masks if they go out in public. This is a shift in federal guidance reflecting new concerns that the coronavirus is being spread by infected people who have no symptoms. Until now, the C.D.C., like the W.H.O., has advised that ordinary people don’t need to wear masks unless they are sick and coughing. Part of the reason was to preserve medical-grade masks for health care workers who desperately need them at a time when they are in continuously short supply. Masks don’t replace hand washing and social distancing.

    • 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.

    • How can I help?

      Charity Navigator, which evaluates charities using a numbers-based system, has a running list of nonprofits working in communities affected by the outbreak. You can give blood through the American Red Cross, and World Central Kitchen has stepped in to distribute meals in major cities.


“We’re not talking about making a space shuttle,” she said. “We’re talking about making a straightforward piece of equipment that’s quite cheap to manufacture.”

A C.D.C. spokesman was unable to address the Lancet study but said the agency is constantly evaluating new science and “adjusts its guidance accordingly.”

No precaution is a guarantee against infection. But the new report estimates how effective some of them seem to be.

Standing more than three feet away cuts the risk of transmission to 3 percent from 13 percent, the analysis found. Use of masks reduces the odds of infection to 3 percent from 17 percent, and eye protection to 6 percent from 16 percent. The researchers emphasized that people should also continue to wash their hands frequently.

The review also offers some practical information for disease models. For example, it suggests that contact tracing for people who are potentially exposed should include anyone who has been within six feet of an infected person.

The analysis is based on observational studies conducted during the coronavirus pandemic, as well as the SARS and MERS epidemics. It can offer only moderate certainty — although the study “underplays the results,” Dr. Michaels said.

The evidence is strong enough to warrant changes to recommendations for essential health care workers and to plan for mass production of N95 masks, Dr. Michaels said.

“The Trump administration needs to be less worried about producing meat, and more about producing N95s and other P.P.E. needed to save the lives of essential workers,” he said.

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