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

SPS commentary:

Infection with SARS-CoV-2 occurred in 42 participants recommended masks and 53 control participants (1.8% vs. 2.1%; odds ratio, 0.82; 95% CI, 0.54 to 1.23]; p =0.33). The researchers note that although the difference observed was not statistically significant, the 95% CIs are compatible with a 46% reduction to a 23% increase in infection. They acknowledge that the findings are limited by missing data, variable adherence, patient-reported findings on home tests, no blinding, and no assessment of whether masks could decrease disease transmission from mask wearers to others.

An editorial points out two aspects that are important to note. First, the study examined the effect of recommending mask use, not the effect of actually wearing them. Second, the effect of a mask recommendation also depends on many other factors, including the prevalence of the virus, social distancing behaviours, and the frequency and characteristics of gatherings. Mask wearing is just one of several interacting strategies to reduce viral transmission, with each reinforcing the others.

It discusses why the Annals published this study if it was not designed to answer a key public health question regarding widespread mask wearing as source control and did not provide a precise estimate of the personal protective effect of masks. More so, against a background of fierce resistance to mask recommendations by leaders and the public in some locales, where these findings  could easily be misused by those opposed to mask recommendations.

It suggests that it might be more irresponsible not publish the results of carefully designed research because the findings were not as favourable or definitive as some may have hoped, and it is important to publish the findings and carefully highlight the questions that the trial does and does not answer.