Effectiveness of Adding a Mask Recommendation to Other Public Health Measures to Prevent SARS-CoV-2 Infection in Danish Mask Wearers

Abstract (PubMed)

Background: Mask wearing has been advocated as a way to prevent SARS-CoV-2 infection. Methods: Randomized controlled trial in Denmark, April-June 2020. Participants (n=4,792) were randomly assigned 1:1 to wear surgical face masks (TYPE II EN 14683, filtration 98%) or no masks when outside the home. The primary outcome was infection with SARS-CoV-2, detected by serology or PCR. Results: Among 4,517 participants who completed the study, 42 of 2,392 (1.8%) in the mask group and 53 of 2,470 (2.1%) in the control group were diagnosed with SARS-CoV-2 infection. The between-group difference was -0.3 percentage points (95% CI, -1.2 to 0.4 pp; P=0.38), with an odds ratio of 0.82 (95% CI, 0.54 to 1.23; P=0.33). Conclusions: The findings are inconclusive, with CIs compatible with a 46% decrease to a 23% increase in infection with SARS-CoV-2 among mask wearers.