Facemasks to prevent transmission of respiratory illness, such as COVID-19

Plain language summary: In March 2021 we searched for systematic reviews that analyse and summarise the effectiveness of facemasks on respiratory virus transmission, such as COVID-19. We found one systematic review of high quality. This high-quality systematic review analyses and summarises the effectiveness of facemasks versus no facemasks or different types of facemasks. All types of populations and settings are included. We have communicated the relevant findings of this systematic review as a short communication product called «Briefly summarised». This systematic review searched for studies in April 2020 and does not include studies on COVID-19. Thus, this high-quality systematic review provides indirect evidence regarding COVID-19. In the process of making this rapid overview we found that it would be very helpful to make a thorough map of the relevant primary studies included in the systematic reviews in one place