1. Adding a mask recommendation to other public measures did not reduce the SARS-Cov-2 infection by more than 50%.
2. Having a mask recommendation did not significantly alter the SARS-CoV-2 infection rate among mask wearers.
Evidence Rating Level: 1 (Excellent)
Study Rundown: Although many localities recommend masks in community settings to prevent the transmission of SARS-CoV-2, the World Health Organization has acknowledged the lack of evidence that wearing a mask protects healthy persons from SARS-CoV-2. Prior observational studies reported that mask use reduced risk for SARS-CoV-2, though surgical and cloth masks were grouped in preventive studies. Observational evidence also indicates that mask-wearing mitigates SARS-CoV-2 transmission, but there is a gap in knowledge as to whether a recommendation to wear a surgical mask when outside the home among others reduces wearers’ risk for SARS-CoV-2 infection in setting where public health measures were in effect but community mask-wearing was uncommon and not recommended. This study demonstrated that the recommendation to wear surgical masks did not significantly reduce the SARS-CoV-2 infection rate among wearers. This study was limited by factors such as inconclusive results, missing data, variable adherence, patient-reported findings on home tests, now blinding, and no assessment of whether masks could decrease transmission from mask wearers to others. Nevertheless, these study’s findings are significant, as they demonstrate that the recommendation to wear a mask did not reduce the incidence of SARS-CoV-2 infection in mask wearers, though the findings were inclusive and the trial did not address the effects of masks as a source control or as protection in settings where social distancing and other public measures are not in effect.
Click to read the study in AIM
Relevant Reading: The Role of Masks in Mitigating the SARS-CoV-2 Pandemic: Another Piece of the Puzzle
In-Depth [randomized control trial]: This randomized control trial was conducted in Denmark between April and May 2020, studying a total of 4862 patients. Patients who were community-dwelling adults aged 18 years or older without current or prior symptoms or diagnosis of COVID-19 who reported being outside the home among others for at least 3 hours per day and who did not wear masks during their daily work were eligible for the study. Patients who were prior mask wearers for their daily work or had prior diagnoses of COVID-19 were excluded from the study. The primary outcome measured was SARS-CoV-2 infection, defined as a positive result on an oropharyngeal/nasal swab test for SARS-CoV-2, or a hospital-based diagnosis of SARS-CoV-2 infection or COVID-19. Outcomes of the primary analysis were assessed via the chi-square test and odds ratios and confidence limits were calculated using logistic regression. Based on the analysis, the between-group difference in infection with SARS-CoV-2 was negative 0.3% (95% Confidence Interval [CI], -1.2 to 0.4%; odds ratio, 0.82 [95% CI, 0.54 to 1.23]). Infection with SARS-CoV-2 occurred in 1.8% of participants who recommended masks and 2.1% of the control participants. When the analysis was repeated with multiple imputations for missing data due to loss to follow-up, there were similar results (OR 0.81, 95% CI 0.53 to 1.23). Overall, this study demonstrates the recommendation to wear a surgical mask when outside the home did not significantly reduce the incidence of SARS-CoV-2 infection in mask wearers in a setting where social distancing and other public health measures were in effect and community use of masks was uncommon.
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