Danish Study to Assess Face Masks for the Protection Against COVID-19 Infection

Effectiveness of Adding a Mask Recommendation to Other Public Health Measures to Prevent SARS-CoV-2 Infection in Danish Mask Wearers: A Randomized Controlled Trial: Annals of Internal Medicine: Vol 0, No 0¹

Hats off to Jefferey Jaxen and the team at The HighWire with Del Bigtree on this ‘breaking news’:² The largest randomized controlled trial on the subject to date. The CDC says “Protect Yourself and Others”.³⁴ So, do masks really make an appreciable difference in protecting you against contracting SARS-CoV-2? What was the outcome of this study? Here’s the relevant excerpt:

Results:

A total of 3030 participants were randomly assigned to the recommendation to wear masks, and 2994 were assigned to control; 4862 completed the study. Infection with SARS-CoV-2 occurred in 42 participants recommended masks (1.8%) and 53 control participants (2.1%). The between-group difference was −0.3 percentage point (95% CI, −1.2 to 0.4 percentage point; P = 0.38) (odds ratio, 0.82 [CI, 0.54 to 1.23]; P = 0.33). Multiple imputation accounting for loss to follow-up yielded similar results. Although the difference observed was not statistically significant, the 95% CIs are compatible with a 46% reduction to a 23% increase in infection. [emphasis added]

Conclusion:

The recommendation to wear surgical masks to supplement other public health measures did not reduce the SARS-CoV-2 infection rate among wearers by more than 50% in a community with modest infection rates, some degree of social distancing, and uncommon general mask use. The data were compatible with lesser degrees of self-protection. [emphasis added]

Anecdotal Findings:

Despite efforts to marginalize (spin) the findings,⁵ this study seems to clearly indicate two things:

1. Masks are insignificant (“−0.3 percentage point”) in preventing infection to the wearer.
2. The overall infection rate itself (1.8 – 2.1%) in a diverse environment (Denmark, April and May 2020) including a wide variety of prophylaxis and mitigation efforts (or lack thereof) is also insignificant.

Footnotes