This is a paper by the New and Emerging Respiratory Virus Threats Advisory Group (NERVTAG) for the Scientific Advisory Group for Emergencies (SAGE), which in turn advises the Government on its response to the Coronavirus threat. This paper is therefor influential in the Government’s policies on the use of facemasks.
NERVTAG paper: face mask use in the community Background • This document summarises evidence o face mask use in the community on the transmission of SARS-CoV-2 to date and options for their use. • This issue is considered in the context of the current control mechanisms of workplace closure and social distancing. Recommendations may change as the epidemic and control measures evolve.
• Mechanistic studies of the effect of face mask use on viral shedding in symptomatic patients involve few patients but show that masks reduce expulsion of infectious particles and therefore may reduce transmission if worn by infected individuals.
• Modelling studies are theoretical and highly dependent on initial assumptions of mask effectiveness. They report a potential major benefit of universal face mask wearing, especially if masks are assumed to be highly effective. In the context of limited mask supply models suggest that it should be targeted at symptomatic infectious patients and those at high risk of severe disease.
• There is weak evidence that use of face masks by symptomatic people may reduce transmission.
• Evidence from randomised trials do not show a protective effect of face masks in community settings but are often affected by low adherence.
• Evidence from observational studies tend to support a protective effect of wearing face masks in the community but results are heterogeneous and subject to major biases and residual confounding.
Also worth a read is another science-based paper prepared for the Government that asks the question “Does the use of face marks in the general population make a difference to spread of infection?” Read Paper