The final and major update to a rapid, living review of published evidence suggests that masks may be associated with a small reduction in risk for COVID-19 infection in community settings versus no mask use, and both surgical masks and N95 respirators may be associated with similar infection risk in routine patient care settings. However, a beneficial effect of N95 respirators could not be ruled out in the health care setting. 

The review is published in Annals of Internal Medicine

In June 2020, Annals published an initial living review of research on mask use which found insufficient evidence to determine effects of masks on COVID-19 infection. The initial review was followed by eight brief updates that found low- to moderate-strength evidence for an association between mask use and decreased risk for SARS-CoV-2 infection in community settings, but evidence on N95 versus surgical masks in health care settings and risk for COVID-19 infection remained insufficient. 

This ninth and final review is different because it includes enough evidence to be considered a major update, according to a release from the American College of Physicians.

Investigators from Oregon Health & Science University reviewed three randomized trials and 21 observational studies to update an evidence synthesis on N95, surgical, and cloth mask effectiveness in community and health care settings for preventing SARS-CoV-2 infection. The authors found that mask use may be associated with a small, reduced risk for COVID-19 infection versus no mask use in community settings.

However, they note that the interventions, settings, and populations included in the reviewed studies varied and adherence was suboptimal, which may have impacted outcomes. The authors also note that trial and observational studies of surgical or N95 mask use compared with no mask were imprecise or limited, with evidence on other mask comparisons in health care settings remaining insufficient. 

An accompanying editorial by Annals editor-in-chief Christine Laine, MD, MPH, and deputy editor Stephanie Chang, MD, MPH, provides important context for understanding why recent evidence reviews do not provide a definitive answer about the benefits of masking. Studies vary widely in what they are designed to determine, such as the effectiveness of masks at preventing viral penetration or the effectiveness of masking recommendations. 

Because these studies are conducted in the real world where infection risk-reduction strategies also vary, it may be difficult to determine the effectiveness of a single component of that strategy. And finally, the authors say we must be explicit in weighing benefits and harms. While some may consider any evidence of benefit sufficient to justify masking, others believe that inconvenience, discomfort, or communication impedance outweigh small benefits. 

To get to the truth about masking, the authors say it is imperative to design studies that fill information gaps, interpret the evidence accurately, and are honest about what we do and do not know.