> A large, randomized trial led by researchers at Stanford Medicine and Yale University has found that wearing a surgical face mask over the mouth and nose is a

> A large, randomized trial led by researchers at Stanford Medicine and Yale University has found that wearing a surgical face mask over the mouth and nose is an effective way to reduce the occurrence of COVID-19 in community settings. > The researchers enrolled nearly 350,000 people from 600 villages in rural Bangladesh. Those living in villages randomly assigned to a series of interventions promoting the use of surgical masks were about 11% less likely than those living in control villages to develop COVID-19, which is caused by infection with the SARS-CoV-2 virus, during the eight-week study period. The protective effect increased to nearly 35% for people over 60 years old. https://med.stanford.edu/news/all-news/2021/09/surgical-masks-covid-19.html https://med.stanford.edu/news/all-news/2021/09/surgical-mask... Earlier studies said there wasn’t sufficient evidence, not that masks aren’t effective: > Results: Fourteen studies were included in this study. One preclinical and 1 observational cohort clinical study found significant benefit of masks in limiting SARS-CoV-2 transmission. Eleven RCTs in a meta-analysis studying other respiratory illnesses found no significant benefit of masks (±hand hygiene) for influenza-like-illness symptoms nor laboratory confirmed viruses. One RCT found a significant benefit of surgical masks compared with cloth masks. > Conclusion: There is limited available preclinical and clinical evidence for face mask benefit in SARS-CoV-2. RCT evidence for other respiratory viral illnesses shows no significant benefit of masks in limiting transmission but is of poor quality and not SARS-CoV-2 specific. There is an urgent need for evidence from randomized controlled trials to investigate the efficacy of surgical and cloth masks on transmission of SARS-CoV-2 and user reported outcomes such as comfort and compliance. https://pubmed.ncbi.nlm.nih.gov/33565274/ https://pubmed.ncbi.nlm.nih.gov/33565274/ The cost of wearing a mask is basically zero when there is sufficient supply. While waiting to gather evidence, it seems like an easy low cost precaution while gathering evidence. Slate Star Code (March 2020): > Please don’t buy up masks while there is a shortage and healthcare workers don’t have enough. > If the shortage ends, and wearing a mask is cost-free, I agree with the guidelines from China, Hong Kong, and Japan – consider wearing a mask in high-risk situations like subways or crowded buildings. Wearing masks will not make you invincible, and if you risk compensate even a little it might do more harm than good. Realistically you should be avoiding high-risk situations like subways and crowded buildings as much as you possibly can. But if you have to go in them, yes, most likely a mask will help. https://slatestarcodex.com/2020/03/23/face-masks-much-more-than-you-wanted-to-know/ https://slatestarcodex.com/2020/03/23/face-masks-much-more-t...