A brief communication published yesterday in Nature Medicine concludes that “results indicate that surgical face masks could prevent transmission of human coronaviruses and influenza viruses from symptomatic individuals”.

Study: "Surgical face masks significantly reduced detection of influenza virus RNA in respiratory droplets...Our results indicate that surgical face masks could prevent transmission of human coronaviruses and influenza viruses from symptomatic individuals" https://t.co/omXFMVD83b — Scott Gottlieb, MD (@ScottGottliebMD) April 3, 2020

This study began in 2013 and recruited participants with confirmed respiratory illness. The researchers had participants wear a mask and measured exhaled breaths by having volunteers sit in a booth and breathe into a collecion device called the Gesundheit-II. Though participants were instructed to breath naturally, many coughs were also recorded in the data.

For the coronaviruses in this study, no droplet particles or aerosols were detected in the exhaled breath of subjects wearing surgical masks. These weren’t Sars-CoV-2 infections, but the results are promising.

A figure from the study shows how many viral particles were detected without mask (second from right) and with mask (far right). The difference is statisically significant.

This study follows an earlier communication to The Lancet early in March where the authors said

WHO recommends against wearing masks in community settings because of lack of evidence. However, absence of evidence of effectiveness should not be equated to evidence of ineffectiveness

by the study authors urging policymakers to “reconsider the role of masking”