To definitively answer the question of whether face masks protect against the novel coronavirus, here’s what you’d need to do:
- Recruit thousands of volunteers.
- Randomly divide them into two groups.
- Assign one group to always wear masks outside of the house, and one group to never wear masks.
- Wait a few months, see who gets infected — then try to sort out all possible confounding variables, like compliance, mask fit and social distancing.
A study like that would be not only tough to pull off, but unethical in the midst of a pandemic. It also wouldn’t be able to determine community-level effectiveness — that is, how well masks work not just to protect individuals, but to reduce the spread of the disease through a population. For that, you would need multiple experimental groups across multiple cities — which isn’t going to happen.
So officials considering mask mandates — as well as citizens weighing how and when to mask up — are forced to act on imperfect evidence. But the path is getting clearer as the sheer volume and variety of studies increases. Some are still preliminary and none meet the so-called gold standard of large, randomized, controlled trials. But collectively they are building a compelling case for universal masking as a low-tech way to help rein in the spread of the virus, and perhaps avoid the need for more painful restrictions.
The new research comes from laboratory tests of masks; observational reports and deep dives into the data from places where masks were and weren’t embraced. There are compelling case studies, including a beauty shop in Missouri where mask-wearing by two unknowingly infected beauticians and dozens of customers seems to have prevented an outbreak. Then there’s the summer camp in Georgia where kids sang and cheered and didn’t wear masks, and more than 250 people got infected.
Modelers at the University of Washington and elsewhere are now leveraging the data that does exist to estimate how many lives might be saved if most people wear masks.
“I don’t think there’s any doubt anymore about the role of masks,” said Dr. Jared Baeten, vice dean of the University of Washington School of Public Health. Baeten was among those who initially questioned the value of masks for the general public, partly to preserve the supply for health care workers, partly because disease prevalence was low, and partly because he — like many other epidemiologists — mistakenly assumed the virus was mainly spread by people with symptoms, who were always advised to wear masks.
What changed his mind was the growing realization that people seem to be most contagious before they feel sick and that some infected people never develop symptoms at all.