One study, published April 6 in the journal Annals of Internal Medicine, found that they did not. That study, led by South Korean researchers, involved asking four patients with COVID-19 to cough into a petri dish 7.8 inches (20 centimetres) away. The patients coughed without masks, while wearing a disposable surgical mask and again wearing a 100% cotton Tube Mask. Neither mask meaningfully decreased the viral load coughed onto the petri dishes. But experts not involved in the study who were contacted by Live Science were hesitant to put much stock into the findings. The researchers didn’t look at distances beyond 7.8 inches to see if droplets didn’t travel as far while people were wearing masks, Chu said.
The study also returned the odd result that most swabs from the outside of patient Custom Mask were positive for corona virus and most from the inside were negative. The authors speculate that perhaps turbulent jets of air from coughing carried the virus toward the outside of the mask, but the explanation wasn’t very satisfying, according to Jones. The other study, published April 3 in the journal Nature Medicine, used a more sophisticated method of collecting the virus particles that sick people emit. The researchers asked 426 volunteers to breathe for 30 minutes into a cone-like device that captures everything exhaled. Of these, 43 patients had influenza, 54 patients had rhinoviruses and 17 patients had seasonal corona viruses (the kinds that cause colds, not the kind that causes COVID-19). This method allowed the researchers to quantify how much virus was found in droplet particles, which are greater than 0.0002 inches (5 microns) in diameter, versus aerosol particles, which are 5 microns or smaller. The participants were randomized to either wear a surgical mask or not wear a mask during the study.
But what does the evidence say about how well face masks work, and who should wear them?
When someone with Covid-19 wears a face mask, they can prevent other people from being infected. It’s also vital for healthcare workers to wear face masks (and to have masks available to wear), both during surgery and routine procedures, to prevent patients becoming infected. Health workers are highly trained experts who know how to correctly use face masks. The masks they use are medical grade equipment and are far more effective than their cloth alternatives.
We can’t automatically assume that because face masks work in hospitals, they will work everywhere. The reason masks are effective in hospitals is partly because they are changed often and correctly fitted, and partly because health workers know how to remove the mask without becoming infected from their outer surface, which could harbour viruses. There is a lack of good, robust evidence on the effectiveness of standard face masks worn by the public. One of the best forms of evidence in medical research is a randomised controlled trial. Typically, these are blinded, where information that may influence participants is withheld until after the experiment is completed. We would have difficulty doing this kind of trial of face masks, because it’s impossible for participants to be unaware of whether or not they’re wearing a mask.
The study also returned the odd result that most swabs from the outside of patient masks were positive for corona virus and most from the inside were negative. The authors speculate that perhaps turbulent jets of air from coughing carried the virus toward the outside of the mask, but the explanation wasn’t very satisfying, according to Jones.