Chou R, Dana T Major Update: Masks for Prevention of SARS-CoV-2 in Health Care and Community Settings-Final Update of a Living, Rapid Review. Ann Intern Med. 2023 May 16. doi: 10.7326/M23-0570. (Systematic review)

BACKGROUND: Optimal use of masks for preventing COVID-19 is unclear.

PURPOSE: To update an evidence synthesis on N95, surgical, and cloth mask effectiveness in community and health care settings for preventing SARS-CoV-2 infection.

DATA SOURCES: MEDLINE, EMBASE, medRxiv (3 June 2022 to 2 January 2023), and reference lists.

STUDY SELECTION: Randomized 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 EXTRACTION: Two investigators sequentially abstracted study data and rated quality.

DATA SYNTHESIS: Three 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.

LIMITATION: Few 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.

CONCLUSION: Updated 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.


Discipline Area Score
Public Health 7 / 7
Infectious Disease 6 / 7
Occupational and Environmental Health 5 / 7
Hospital Doctor/Hospitalists 5 / 7
Internal Medicine 5 / 7
Comments from MORE raters

Infectious Disease rater

This is another review that elucidates the complexity of attempting to implement a behavioral intervention to combat a respiratory virus. As confounders abound and study heterogeneity limits the combination of most studies, this paper's results (like the several others previously published) indicate the problems of studying behavioral interventions rather than the effectiveness of masking.

Occupational and Environmental Health rater

A well performed systematic review but substantially limited by the poor quality of the evidence informing this question. Useful for clinicians to know about the potential community benefit, but also to recognize that additional data would be of significant value to address this question for healthcare workers.

Occupational and Environmental Health rater

Does masking work? This review leaves the answer up in the air. For health care, they did not address several important factors: Most health care workers acquired Covid-19 in the community, impacting the numbers. We unequivocally saw a drop in other upper respiratory infections, like influenza, with masking. There was little worker-to- worker transmission when masking was in place.

Occupational and Environmental Health rater

The benefits of wearing a face mask to reduce risk of Covid-infection has been and still is a matter of debate. It seems still of minimal risk to use, although its benefit may not be overwhelming. Further studies are needed and the mask should also be put in perspective of other simple protective measures such as keeping distance and avoiding work and public communication when infected.
Comments from EvidenceAlerts subscribers

Dr. Stephen Roedde (5/19/2023 8:44 PM)

As with all medical interventions, observational studies are of limited utility. It is perhaps one of the greatest failures of the COVID pandemic, that proper, well funded, and rigorous RCT’s were never done. DANMASK and the study in Bangladesh were the only useful (but imperfect) additions to our knowledge.I believe there is one RCT comparing N95’s with surgical masks in health care settings, still to come, but that is only of peripheral use. Sadly, we know little more now than before COVID, and that is that the evidence for effectiveness of masks in reducing transmission is questionable at best.
The Cochrane review remains the best summary of the evidence.