1. In this open-label randomized controlled trial, with less than 50% adherence to recommendations, a recommendation for surgical masks did not confer statistically significant protection against SARS-CoV-2 infection compared to no recommendation.
Evidence Rating Level: 4 (Below Average)
Study Rundown: Community measures to reduce the transmission of SARS-CoV-2 are imperative as cases increase worldwide. However, it is unclear whether masks are effective in protecting the wearer from SARS-CoV-2 infection. To address this paucity of data, the authors undertook an open-label, randomized trial of encouragement to wear a surgical mask vs. no recommendation to wear a mask with both groups recommended continuing social distancing guidelines. In Denmark at the time of the trial, social distancing guidelines were in effect but mask-wearing by the general public was not common. Infection was detected in 42 participants in the mask group and 53 in the control group but the infection rate difference was not statistically significant even after accounting for loss to follow-up. There was no significant difference for infections with other detectable respiratory viruses between the mask and no mask group. This trial was severely limited by several factors such as the biased nature of self-reported adherence, loss of patient data in follow-up, variable level of proper technique in mask use, behavior changes with mask use that were not addressed, and durability loss depending on variable environments. The authors highlight that a protective effect is not ruled out by their study. This is particularly pertinent in the context of recent Centers for Disease Control and Prevention recommendations that cloth masks do provide wearer protection. The findings of this study do not belie these guidelines given the severe limitations of this study and should not be used as evidence against wearing masks.
Click here to read the study in Annals of Internal Medicine
Relevant Reading: Physical distancing, face masks, and eye protection to prevent person-to-person transmission of SARS-CoV-2 and COVID-19: a systematic review and meta-analysis
In-Depth [randomized controlled trial]: In this randomized, open-label trial, 3030 participants were randomized to encouragement for mask-wearing with a supply of masks and 2994 patients were randomized to control. 4862 patients (80.7%) completed the study. Adherence was variable, where 46% reported wearing as recommended, 47% predominately as recommended and 7% not as recommended. From the intention-to-treat analysis, The between-group difference between the mask wearers and control was -0.3% difference (95% Confidence Interval, -1.2 to 0.4%, p = 0.38). The odds ratio (OR) of infection was 0.82 (95% CI, 0.54 to 1.23, p = 0.33). After imputation for missing data due to loss of follow-up, the OR was 0.81 (95% CI, 0.53 to 1.23, p = 0.32). In patients who wore masks “exactly as instructed”, the between-group difference was -0.2% (95% CI, -1.3 to 0.9, p = 0.82). Further, for other respiratory viral infections, there was no difference (-0.1%, 95% CI, -0.6 to 0.4, p = 0.87).
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