Alliance for Pandemic Preparedness

November 19, 2020

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

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  • An individually randomized controlled trial in Denmark from April to May 2020 (n=4,862) found that among participants spending at least 3 hours outside of home per day without occupational mask use and already practicing physical distancing, the intervention to recommend wearing a surgical mask when outside of home did not significantly reduce SARS-CoV-2 infection among mask wearers (OR = 0.82, 95% CI 0.54-1.23). Infection occurred in 42 participants recommended to wear masks (1.8%), compared to 53 participants in the control arm (2.1%). Accounting for loss to follow-up (19%) and mask use non-adherence (7%) yielded similar results.
  • Key study limitations include 46% who reported adherence to wearing the mask as recommended and 47% who reported wearing the mask predominantly as recommended. The authors note that study findings are in the context of implementation of other public health measures, including social distancing, limiting contacts, and restaurant closures – including part of the trial occurring during lockdown. [EDITORIAL NOTE: This trial evaluated only the outcome of infections among people instructed to wear a mask, and not the effect of wearing masks on decreasing transmission to other people.]

Bundgaard et al. (Nov 18, 2020). Effectiveness of Adding a Mask Recommendation to Other Public Health Measures to Prevent SARS-CoV-2 Infection in Danish Mask Wearers. Annals of Internal Medicine. https://doi.org/10.7326/M20-6817