Be sure to read the follow up letter to NEJM by the same authors...
*****************************************************************************
To the Editor

We understand that some people are citing our Perspective article (published on April 1 at NEJM.org)1 as support for discrediting widespread masking. In truth, the intent of our article was to push for more masking, not less. It is apparent that many people with SARS-CoV-2 infection are asymptomatic or presymptomatic yet highly contagious and that these people account for a substantial fraction of all transmissions.2,3 Universal masking helps to prevent such people from spreading virus-laden secretions, whether they recognize that they are infected or not.4

We did state in the article that “wearing a mask outside health care facilities offers little, if any, protection from infection,” but as the rest of the paragraph makes clear, we intended this statement to apply to passing encounters in public spaces, not sustained interactions within closed environments. A growing body of research shows that the risk of SARS-CoV-2 transmission is strongly correlated with the duration and intensity of contact: the risk of transmission among household members can be as high as 40%, whereas the risk of transmission from less intense and less sustained encounters is below 5%.5-7 This finding is also borne out by recent research associating mask wearing with less transmission of SARS-CoV-2, particularly in closed settings.8 We therefore strongly support the calls of public health agencies for all people to wear masks when circumstances compel them to be within 6 ft of others for sustained periods.

Michael Klompas, M.D., M.P.H.
Harvard Medical School, Boston, MA

Charles A. Morris, M.D., M.P.H.
Brigham and Women’s Hospital, Boston, MA

Erica S. Shenoy, M.D., Ph.D.
Massachusetts General Hospital, Boston, MA

Since publication of their article, the authors report no further potential conflict of interest.

This letter was published on June 3, 2020, at NEJM.org.