• Roger Chou and Tracy Dana.
• Pacific Northwest Evidence-based Practice Center and the Department of Medical Informatics and Clinical Epidemiology, Oregon Health & Science University, Portland, Oregon (R.C., T.D.).
• Ann. Intern. Med. 2023 Jun 1; 176 (6): 827835827-835.

BackgroundOptimal use of masks for preventing COVID-19 is unclear.PurposeTo update an evidence synthesis on N95, surgical, and cloth mask effectiveness in community and health care settings for preventing SARS-CoV-2 infection.Data SourcesMEDLINE, EMBASE, medRxiv (3 June 2022 to 2 January 2023), and reference lists.Study SelectionRandomized trials of interventions to increase mask use and risk for SARS-CoV-2 infection and observational studies of mask use that controlled for potential confounders.Data ExtractionTwo investigators sequentially abstracted study data and rated quality.Data SynthesisThree randomized trials and 21 observational studies were included. In community settings, mask use may be associated with a small reduced risk for SARS-CoV-2 infection versus no mask use, on the basis of 2 randomized trials and 7 observational studies. In routine patient care settings, surgical masks and N95 respirators may be associated with similar risk for SARS-CoV-2 infection, on the basis of 1 new randomized trial with some imprecision and 4 observational studies. Evidence from observational studies was insufficient to evaluate other mask comparisons due to methodological limitations and inconsistency.LimitationFew randomized trials, studies had methodological limitations and some imprecision, suboptimal adherence and pragmatic aspects of randomized trials potentially attenuated benefits, very limited evidence on harms, uncertain applicability to Omicron variant predominant era, meta-analysis not done due to heterogeneity, unable to formally assess for publication bias, and restricted to English-language articles.ConclusionUpdated evidence suggests that masks may be associated with a small reduction in risk for SARS-CoV-2 infection in community settings. Surgical masks and N95 respirators may be associated with similar infection risk in routine patient care settings, but a beneficial effect of N95 respirators cannot be ruled out.Primary Funding SourceNone.

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