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:
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]
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]
Despite efforts to marginalize (spin) the findings,5 this study seems to clearly indicate two things:
- Masks are insignificant (“−0.3 percentage point”) in preventing infection to the wearer.
- 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.
- Johan Skov Bundgaard, Daniel Emil Tadeusz Raaschou-Pedersen, Christian von Buchwald, et al. 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 0;0 [Epub ahead of print 18 November 2020]. doi:https://doi.org/10.7326/M20-6817 ↩
- NEW STUDY CASTS DOUBT ON MASK EFFICACY – The Highwire ↩
- CDC Print Resources: Meeting Friends? Protect Yourself and Others from COVID-19 How to protect yourself and your friends from COVID-19. Date: 10/26/20 Audience: General Public ↩
- Coronavirus disease 2019 (COVID-19) How To Protect Yourself – prevention-H.pdf ↩
- Denmark trial measures effectiveness of adding a mask recommendation to other public health measures for preventing SARS-CoV-2 infection | ACP Newsroom | ACP ↩