Scientists agree that wearing a mask helps stop infected people from spreading the coronavirus—but there is some disagreement over how much they protect the wearer. A Danish study conducted early in the pandemic, when few Danes wore masks in public, found that masks did not offer as much protection to the wearer as expected, the New York Times. Researchers had expected the risk of infection would be halved among the group given surgical masks and told to wear them outside the home. Instead, 1.8% of the mask-wearers got infected, compared to 2.1% of the group told not to wear masks. "The study thereby fails to confirm the expected halving of risk of infection for the wearer of the face mask, but the results could suggest a moderate level of protection of 15% to 20%," researchers said in a statement, per the Local.
Other experts said they had doubts about the study, which involved 6,000 people starting in early April. It happened when infection rates were relatively low, and with participants reporting their own results, mask-wearing was not independently verified. The CDC updated its guidance this week, saying multiple studies had found masks help stop users from breathing in infected droplets. Former CDC director Dr. Thomas Frieden says much depends on the type of mask being used, and how much virus a person is exposed to. The Danish study was published in the Annals of Internal Medicine; editor-in-chief Dr. Christine Laine said the study shows the need to adhere to social distancing guidelines and other precautions. "There are people who say, 'I’m fine, I'm wearing a mask,'" she said. "They need to realize they are not invulnerable to infection." (Read more face masks stories.)