Print page Print page
Switch language
Rigshospitalet - a part of Copenhagen University Hospital

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

Research output: Contribution to journalJournal articleResearchpeer-review


  1. Ethical and Scientific Considerations Regarding the Early Approval and Deployment of a COVID-19 Vaccine

    Research output: Contribution to journalEditorialpeer-review

  2. Chylomicronemia From GPIHBP1 Autoantibodies Successfully Treated With Rituximab: A Case Report

    Research output: Contribution to journalLetterpeer-review

  3. Breast Cancer Screening and Diagnosis

    Research output: Contribution to journalLetterpeer-review

  4. Patent Foramen Ovale: A Villain in Pulmonary Embolism?

    Research output: Contribution to journalJournal articleResearchpeer-review

  1. Capsid-like particles decorated with the SARS-CoV-2 receptor-binding domain elicit strong virus neutralization activity

    Research output: Contribution to journalJournal articleResearchpeer-review

  2. Sequelae of Major Trauma Patients with Maxillofacial Fractures

    Research output: Contribution to journalJournal articleResearchpeer-review

  3. Impact of time to treatment initiation for patients with oral cavity squamous cell carcinoma: a population-based, retrospective study

    Research output: Contribution to journalJournal articleResearchpeer-review

  4. Incidence and survival of salivary gland cancer in children and young adults in Denmark: A nation-wide study for the period 1990-2015

    Research output: Contribution to journalJournal articleResearchpeer-review

View graph of relations

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]). ( 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.

Original languageEnglish
JournalAnnals of Internal Medicine
Issue number3
Pages (from-to)335-343
Number of pages9
Publication statusPublished - 1 Mar 2021

Bibliographical note

This record is sourced from MEDLINE/PubMed, a database of the U.S. National Library of Medicine

ID: 61271101