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Source: United Kingdom – Executive Government & Departments

A randomised control trial (RCT) published by Annals of Internal Medicine assesses mask use as a public health measure to help prevent SARS-CoV-2 infection in Danish mask wearers.

Prof Babak Javid, Associate Professor of Experimental Medicine at the University of California, San Francisco, said:

“Unlike the situation at the beginning of the COVID pandemic, the majority of countries in the world now have some form of mask mandate to protect the population. There is a wealth of observational data to support mask use, but randomised controlled data on mask efficacy in a population setting is lacking in this context.

“Here, scientists in Denmark embarked on a randomised controlled trial of surgical mask use (or not) in the early phase of the first wave of the pandemic. All volunteers were asked to adhere to public health guidance (e.g. distancing, hygiene etc) and were then randomised to wearing surgical masks or not. The number of COVID-19 cases between the two groups after one month of randomisation was measured by antibody testing.

“The results were disappointing: mask usage was not associated with significant protection, although there was a great deal of uncertainty associated with the finding (ranging from c. 40% protection to 20% exacerbation).

“The authors are honest about the major limitations of their study: the study was conducted at a time when much of the country had some form of lockdown, limiting exposures outside of the household, and was not powered to detect smaller than 50% efficacy. The authors also didn’t measure mask compliance: either in the mask group (did they wear a mask when they were supposed to?) and in the unassigned group (did they wear a mask anyway?), and even small differences here could muddy interpretation of the results given the small number of COVID cases. Most importantly, the study could not measure the efficacy of arguably the most important aspect of how population mask wearing may influence outcomes in the pandemic: as ‘source control’ i.e. limit transmission of SARS-CoV2 by the wearer.

“Nonetheless, the authors should be congratulated on performing the study at all, at a time when most governments resisted mask mandates, but also didn’t engage in performing studies on potential efficacy. ”


Effectiveness of Adding a Mask Recommendation to Other Public Health Measures to Prevent SARS-CoV-2 Infection in Danish Mask Wearers’ by Henning Bundgaard et al. was published in Annals of Internal Medicine on Wednesday 18th November 2020.

DOI: 10.7326/M20-6817

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MIL OSI United Kingdom