Masks for Prevention of Respiratory Virus Infections

Chou R, Dana T, Jungbauer R, Weeks C, McDonagh MS.
Masks for Prevention of Respiratory Virus Infections, Including SARS-CoV-2, in Health Care and Community Settings. Ann Intern Med 2020;Jun 24:[Epub ahead of print].

This systematic review summarizes the evidence surrounding the effectiveness of N95, surgical, and cloth masks in community and health care settings in preventing respiratory virus infections. This “living” review will continuously be updated as new data arise. The following are key points to remember:

  1. The authors identified 39 studies (18 randomized controlled trials [RCTs] and 21 observational studies; 33,867 participants), with only two of them pertaining to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).
  2. Disposable N95 masks are fitted devices that have been tested to achieve very efficient filtration of small airborne particles. Surgical masks are loose-fitting, create a physical barrier, block larger particles, and are fluid resistant. Cloth masks are nonmedical face coverings that vary with regard to filtration and fluid resistance depending on the material used, the number of layers, and fit.
  3. To date, there are no studies evaluating the effectiveness of masks for prevention of SARS-CoV-2 infection in the community setting. Two observational studies did address it in the health care setting. N95 respirators are associated with decreased infection risk versus no mask, but mask use was based on whether the individual worked in a department in which masks were used, not on assessment of individual use.
  4. Observational studies show masks were consistently associated with a lower risk of SARS-CoV-1 and Middle East respiratory syndrome (MERS) infection, with N95 masks being more effective than surgical masks.
  5. Randomized trials evaluating the effectiveness of masks were mostly done in the setting of influenza and influenza-like illnesses. Twelve RCTs were performed in the community setting. Most did not show a significant reduction in the risk for influenza with the use of masks. The estimates were however imprecise, and assessments of adherence were limited.
  6. Six RCTs for prevention of influenza or influenza-like illnesses were done in the health care setting. Two of the trials found N95 respirators were associated with a -2.8% to -7.7% decreased risk of respiratory illness compared to surgical masks. One trial in the lower-risk outpatient setting showed no difference comparing N95 to surgical masks for reducing the risks of respiratory illness.
  7. Effectiveness of N95 respirators was similar for fit-tested and nonfit-tested respirators. Continuous use compared to intermittent use was associated with a small decrease in the risk of illness (7.2% vs. 11.8%).
  8. RCTs were limited by the small number of influenza-like cases, and different methods of assessments (laboratory confirmed versus occurrence of clinical symptoms).
  9. There was no evidence of serious harm associated with the use of masks.
  10. Overall, the evidence for the effectiveness of masks in the prevention of respiratory infections is stronger in the health care setting. Evidence specifically supporting the effectiveness of masks for prevention of SARS-CoV-2 infection is lacking. Whether effectiveness can be extrapolated from other studies is unclear.
  11. While the data are limited for the use of masks in reducing the risk of SARS-CoV-2 infection, the low cost of masks, lack of harm, and our understanding of the pathophysiology of respiratory infections support their use until reliable evidence provides new guidance.

Clinical Topics: Prevention

Keywords: Coronavirus Infections, COVID-19, Influenza, Human, Masks, Outpatients, Primary Prevention, Randomized Controlled Trials as Topic, SARS Virus, Severe Acute Respiratory Syndrome, severe acute respiratory syndrome coronavirus 2

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