This document is an update of the guidance published on 6 April 2020 and includes updated scientific evidence relevant to the use of masks for preventing transmission of Coronavirus disease 2019 (COVID-19) as well as practical considerations. The main differences from the previous version include the following:
• Updated information on transmission from symptomatic, pre-symptomatic and asymptomatic people infected with COVID-19, as well as an update of the evidence of all sections of this document;
• New guidance on the targeted continuous use of medical masks by health workers working in clinical areas in health facilities in geographical areas with community transmission1 of COVID-19;
• Updated guidance and practical advice for decisionmakers on the use of medical and non-medical masks by the general public using a risk-based approach;
• New guidance on non-medical mask features and characteristics, including choice of fabric, number and combination of layers, shape, coating and maintenance.