The Centers for Disease Control (CDC) has put out an advisory calling on Americans to wear masks, to help prevent the spread of COVID-19.

“We are not defenseless against COVID-19,” said CDC Director Dr. Robert R. Redfield. “Cloth face coverings are one of the most powerful weapons we have to slow and stop the spread of the virus – particularly when used universally within a community setting.  All Americans have a responsibility to protect themselves, their families, and their communities.”

This CDC release included two case studies out on Tuesday, July 14, one from the Journal of the American Medical Association (JAMA), showing that adherence to universal masking policies reduced SARS-CoV-2 transmission within a Boston hospital system, and one from CDC’s Morbidity and Mortality Weekly Report showing that wearing a mask prevented the spread of infection from two hair stylists to their customers in Missouri.

In a story for the University of California at San Francisco, which focuses on medical research and patient care, Nina Bai spoke with epidemiologist Dr. George Rutherford, M.D., and infectious disease specialist Peter Chin-Hong, M.D.   They said wearing masks is really important now that it’s clearly understood that asymptomatic people can have and can spread the coronavirus.

They noted it would be unethical to test the mask-wearing theory by requiring some people to not wear masks, in the time of a pandemic, to test whether mask-wearing protects people from COVID-19.  But they pointed to some real world case studies.  In one report, a man flew from China to Toronto, wearing a mask.  He had a cough and tested positive for COVID-19.  But all 25 people closest to him on the flight tested negative for COVID-19.   They also referenced the case in late May (as noted by the CDC) where two hair stylists in Missouri had close contact with 140 clients.  The hair stylists had COVID-19, but they and their clients wore masks, and none of the clients tested positive.

Rutherford said if 80% of the people in the country wore masks, that would reduce the spread of COVID-19 more than would lockdowns.    Regarding what type of masks are best, Rutherford and Chin-Hong said whatever mask is comfortable–surgical masks or cloth masks.  They said N-95 masks are not needed for non-medical personnel.  Both Rutherford and Chin-Hong cautioned against N95 masks with valves (commonly used in construction to prevent the inhalation of dust) because they do not protect those around you. These one-way valves close when the wearer breathes in, but open when the wearer breathes out, allowing unfiltered air and droplets to escape.

For the UCSF article, click here.