Researchers from Oregon Health & Science University reviewed multiple electronic databases, including the World Health Organization COVID-19 database and medRxiv preprint server to examine the effectiveness of N95, surgical, and cloth masks in community and healthcare settings for preventing respiratory virus infections, and effects of reuse or extended use of N95 masks. They found that evidence on mask effectiveness for respiratory infection prevention is stronger in healthcare than community settings. Current evidence suggests that use of N95 respirators might reduce SARS-CoV-1 risk versus surgical masks in healthcare settings, but applicability to SARSCoV-2 is uncertain.

For their review, Chou, et al. (2020) consulted multiple electronic databases, including the World Health Organization COVID-19 database and medRxiv preprint server (2003 through 14 April 2020; surveillance through 2 June 2020), and reference lists.

Randomized trials of masks and risk for respiratory virus infection, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and observational studies of mask use and coronavirus infection risk were included. New evidence will be incorporated by using living review methods.

39 studies (18 randomized controlled trials and 21 observational studies; 33 867 participants) were included. No study evaluated reuse or extended use of N95 masks. Evidence on SARS-CoV-2 was limited to 2 observational studies with serious limitations. Community mask use was possibly associated with decreased risk for SARS-CoV-1 infection in observational studies. In high- or moderate-risk healthcare settings, observational studies found that risk for infection with SARS-CoV-1 and Middle East respiratory syndrome coronavirus probably decreased with mask use versus non-use and possibly decreased with N95 versus surgical mask use. Randomized trials in community settings found possibly no difference between N95 versus surgical masks and probably no difference between surgical versus no mask in risk for influenza or influenza-like illness, but compliance was low. In healthcare settings, N95 and surgical masks were probably associated with similar risks for influenza-like illness and laboratory-confirmed viral infection; clinical respiratory illness had inconsistency. Bothersome symptoms were common.

The researchers concluded that evidence on mask effectiveness for respiratory infection prevention is stronger in healthcare than community settings. N95 respirators might reduce SARS-CoV-1 risk versus surgical masks in healthcare settings, but applicability to SARS-CoV-2 is uncertain, they say.

Reference: Chou R, et al. Masks for Prevention of Respiratory Virus Infections, Including SARS-CoV-2, in Health Care and Community Settings: A Living Rapid Review. Ann Intern Med. June 24, 2020.