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.

BACKGROUND: Observational evidence suggests that mask wearing mitigates transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). It is uncertain if this observed association arises through protection of uninfected wearers (protective effect), via reduced transmission from infected mask wearers (source control), or both. OBJECTIVE: To assess whether recommending surgical mask use outside the home reduces wearers' risk for SARS-CoV-2 infection in a setting where masks were uncommon and not among recommended public health measures. DESIGN: Randomized controlled trial (DANMASK-19 [Danish Study to Assess Face Masks for the Protection Against COVID-19 Infection]). (ClinicalTrials.gov: NCT04337541). SETTING: Denmark, April and May 2020. PARTICIPANTS: Adults spending more than 3 hours per day outside the home without occupational mask use. INTERVENTION: Encouragement to follow social distancing measures for coronavirus disease 2019, plus either no mask recommendation or a recommendation to wear a mask when outside the home among other persons together with a supply of 50 surgical masks and instructions for proper use. MEASUREMENTS: The primary outcome was SARS-CoV-2 infection in the mask wearer at 1 month by antibody testing, polymerase chain reaction (PCR), or hospital diagnosis. The secondary outcome was PCR positivity for other respiratory viruses. RESULTS: 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. LIMITATION: Inconclusive results, 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. CONCLUSION: 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. PRIMARY FUNDING SOURCE: The Salling Foundations.

Face masks for the prevention of COVID-19 - Rationale and design of the randomised controlled trial DANMASK-19.

INTRODUCTION: The coronavirus disease 19 (COVID-19) pandemic, caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), progresses globally, and means to reduce the transmission are needed. In the community, the use of face masks is increasing world-wide, but documentation for the efficacy of this remedy is lacking. This trial investigates whether the use of face masks in the community will reduce wearers' risk of SARS-CoV-2 infection. METHODS: This study will be a two-arm, unblinded, randomised controlled trial. We will include adults (>18 years of age) without prior confirmed COVID-19 or symptoms suggestive of COVID-19, who spend more than three hours per day outside the home with exposure to other people. A total of 6,000 participants are randomly assigned 1:1 to use face masks or not for a 30-day period during the pandemic. Participants will perform self-testing; quick test for SARS-CoV-2 antibodies (immunoglobulin M (IgM) and immunoglobulin G (IgG)) (the Livzon lateral flow test) and oropharyngeal/nasal swabs for viral detection using polymerase chain reaction (PCR). The primary endpoint following the 30-day study period is the difference in the number of SARS-CoV-2-infected individuals between the two study groups as assessed by a positive nasopharyngeal swap, a positive antibody test or a hospital-based diagnosis of SARS-CoV-2 infection. CONCLUSIONS: We will study whether a face mask protects the wearer of the mask against SARS-CoV-2 infection. The findings are expected to apply to the present pandemic and to future viral outbreaks and to provide evidence for authority recommendations across the world. FUNDING: This study was funded by Salling Fondene. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT04337541.