The record is narrow but clear. In a study published April 3, 2020 in Nature Medicine, surgical masks worn by infected patients sharply cut the flu virus that could be detected in the droplets they breathed and coughed out. The same masks also lowered the amount of seasonal coronavirus, one of the causes of the common cold, found hanging in the air as aerosols.
The study did not test SARS-CoV-2. “Further research is needed to determine whether masks can specifically prevent the transmission of SARS-CoV-2,” the scientists wrote. At the time of publication the pandemic had infected more than a million people and killed more than 53,000, according to Reuters.
Benjamin Cowling, the professor who led the work at the World Health Organization Collaborating Centre for infectious disease epidemiology in Hong Kong, told Reuters by telephone that the results could be stretched to simpler masks. “My expert view is that cloth or cotton masks would have an effect, but maybe slightly less of an effect than a surgical mask properly worn,” he said. “And in terms of COVID-19, we’re looking at every possible measure that could help.”
What the experiments measured
The University of Maryland said the team captured exhaled breath with the “Gesundheit II machine,” a device built by Dr. Don Milton, a professor of applied environmental health there and a senior author. The experiments were done before the pandemic, together with colleagues at the University of Hong Kong’s Faculty of Medicine. They address one question only: whether a mask keeps an infected person from spreading virus. They say nothing about whether a mask shields the person wearing it.
Milton also challenged the idea that these viruses travel only on large droplets from a cough or sneeze. “What they don’t understand is that is merely a hypothesis,” he said. Tiny aerosolized droplets, his study and earlier ones suggest, can drift through the air, so a person might pick up the virus just by inhaling the breath of someone nearby, symptoms or not. Surgical masks, he said, catch a lot of that exhaled virus.
Limits on the finding
Milton cautioned that the effect may be smaller outside controlled lab conditions. Still, he argued the chance of benefit justified a fresh look at whether everyone should wear masks in shops and other busy places. “In normal times we’d say that if it wasn’t shown statistically significant or the effective in real-world studies, we don’t recommend it,” he said. “But in the middle of a pandemic, we’re desperate.”
The World Health Organization’s position then was that people with a cough or fever, and anyone looking after a patient with confirmed or suspected COVID-19, should wear a mask. It did not advise healthy people to wear one in everyday life. Rupert Beale, an infection biologist at London’s Francis Crick Institute who was not part of the research, called the evidence “strong and compelling” but warned against over-reading it. Masks, he said, “cannot be relied on as a sole measure,” and belong alongside other social distancing steps in any “exit strategy” from lockdown.
Sources
- Masks do reduce spread of flu and some coronaviruses, study finds (Reuters)
- Wearing surgical masks in public may help limit the spread of COVID-19
