Question & Answer

Does wearing a face mask when well prevent COVID-19 infection?
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  • We found six systematic reviews that examined the relationship between face mask-wearing and COVID-19 infection. Five were reviews of non-randomised. One included one RCT. The studies varied substantially in how they were designed and conducted and, apart from the RCT, lacked a comparison group.
  • Most of these reviews reported some evidence that masks were effective at preventing infection and reducing cases or serious outcomes, including deaths from COVID-19. However, these findings are of low certainty because other factors (such as lockdowns, social distancing or changes in peoples’ behaviour) could have caused the difference in infection rates. In addition, it is difficult to be sure that people remember exactly if and when they used masks and what other measures they were taking at the time.
  • Some of these reviews called for further high-quality studies to assess the impact of face mask-wearing in the community.
  • We then looked for RCTs and found two:
    • One of these was included in the systematic review discussed above. This Danish study found that 1.8% of those recommended to wear masks became infected with SARS-CoV-2 compared with 2.1% of those who were not recommended masks; an absolute difference of 0.3%.
    • The second, Bangladeshi, RCT found that 0.68% of those in villages recommended to wear masks became infected with SARS-CoV-2 compared with 76% of those in villages who were not recommended masks; an absolute increase of 0.8% where they were not asked to wear masks.
  • In both trials findings were ‘inconclusive’ meaning that that the results are not definitive, and it’s difficult to draw a clear conclusion or make a firm decision based on the evidence gathered.
  • To help them understand how confident they could be in their results, the researchers in these two trials used a tool called a ‘confidence interval’ (CI); a range of numbers that the researchers think the true answer is probably within. The CIs in the Danish trial suggest that masks could either increase or decrease infection rates. The CIs in the Bangladeshi trial suggest that masks could decrease infections or make no difference.
  • Both trials tried to account for people who did not wear masks correctly (or at all) and found that this made very little difference to their findings.
  • Currently, the WHO advises using masks as part of a comprehensive package for the prevention and control of COVID-19 but notes the ‘limited and inconsistent scientific evidence’ to support that recommendation.
  • Currently, the HSE notes that ‘when worn properly’ masks can reduce the spread of COVID-19.

Things to Remember

Reviewers

  • Lead Researcher: Dr. Paula Byrne, HRB-Trials Methodology Research Network & Evidence Synthesis Ireland, University of Galway
  • Reviewed by: Prof. Declan Devane, School of Nursing and Midwifery, HRB-Trials Methodology Research Network, Evidence Synthesis Ireland & Cochrane Ireland, University of Galway.
  • Topic advisor: Prof. Susan M Smith, Professor of General Practice, Discipline of Public Health and Primary Care, Trinity College Dublin and General Practitioner in Inchicore Family Doctors, Dublin 8.
  • Public and Patient advisor: Anne Daly, Public and Patient Involvement in research (PPI) advisor, PPI Ignite, NUI Galway.
  • Journalist Advisor: Dr. Claire O’Connell, Journalist, Contributor, The Irish Times.

Conflict of Interest Statement: Dr. Paula Byrnewas co-author of several HIQA reports on face masks during the COVID-19 pandemic. She has no other financial or other conflicts of interest for this health claim summary.

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