Most studies of the effectiveness of masks to interrupt disease transmission have focused on prevention of other, non-COVID-19 respiratory diseases, mask use in healthcare settings, and the use of respirators (N95) or surgical masks. There is limited evidence that applies specifically to the question of whether fabric mask use by the general public could limit transmission of SARS-CoV-2.
A recent systematic review of mask use was published in the Lancet and found that wearing a mask in both healthcare and community settings reduced the risk of infection with coronaviruses that cause COVID-19, SARS, or MERS. However, few studies of COVID-19 in non-healthcare (community settings) were available and none were included in the final meta-analysis assessing mask use in community settings. The authors found that mask-wearing was more protective in healthcare facilities than in community settings. This could be because healthcare workers have increased exposure or because N95 respirators are more common in healthcare settings and were found to be more effective than surgical masks or multi-layer fabric masks in preventing infection. It could also be because healthcare staff are more likely to adhere to correct procedures for the safe and effective use of masks. Further, N95 respirators, surgical masks, and multi-layer fabric masks were found to be more protective than single-layer masks. However, the authors suggested that additional, higher quality evidence is needed as all studies included in this review were observational.
A recent retrospective cohort study in China found that if household members wore masks prior to a member becoming noticeably ill with COVID-19, the risk of COVID-19 transmission to healthy family members was reduced.
There are several recent systematic reviews and meta-analyses that have evaluated the impact of mask-wearing on respiratory infection in both healthcare and community settings (Study 1, Study 2, unpublished Study 3, unpublished Study 4, unpublished Study 5). All of these reviews found that there were no available or eligible studies on the impact of fabric face masks on COVID-19 transmission in community settings. Two of these reviews suggest that masks may be protective in community settings (Study 1, unpublished Study 3). One review found some evidence of protective effects for self-reported illness but no effect on laboratory-confirmed illness, and two found limited evidence of a protective effect of surgical masks (Study 2, unpublished Study 4). The strength of evidence varied by study design and outcome definition, complicating the interpretation. All reviews agreed that their analyses were limited by substantial evidence gaps and issues with study quality. Even given limited evidence, the authors of four of the five reviews promoted the use of masks by the public, alongside other preventative measures such as physical distancing and hand hygiene, in at least some community settings.
Want to learn more about mask use for interrupting the spread of COVID-19?
- How could wearing a mask reduce COVID-19 transmission?
- What types of masks are there and what are they designed to do?
- What is a N95 respirator and who should use one?
- What is a surgical mask and who should use one?
- What is a fabric mask, who should use one, and how should they be made?
- What should be considered when making fabric masks?
- Hygienic use of fabric face masks
- What is an occupational mask and who should wear one?
- Why doesn’t the WHO recommend that everyone wears face masks in all settings?
- What can modelling studies tell us about the effectiveness of wearing masks?
- How well do masks work under laboratory (experimental) conditions?
- Do homemade masks increase the risk of respiratory disease?
- How might an evolving understanding of virus transmission affect mask recommendations?
- Should hygiene promotion staff wear masks to protect themselves and others?