Appendix 6 - Supporting data from Effectiveness of face masks for reducing transmission of SARS-CoV-2: a rapid systematic review

This rapid systematic review of evidence asks whether (i) wearing a face mask, (ii) one type of mask over another and (iii) mandatory mask policies can reduce the transmission of SARS-CoV-2 infection, either in community-based or healthcare settings. A search of studies published 1 January 2020–27 January 2023 yielded 5185 unique records. Due to a paucity of randomized controlled trials (RCTs), observational studies were included in the analysis. We analysed 35 studies in community settings (3 RCTs and 32 observational) and 40 in healthcare settings (1 RCT and 39 observational). Ninety five per cent of studies included were conducted before highly transmissible Omicron variants emerged. Ninety one per cent of observational studies were at ‘critical’ risk of bias (ROB) in at least one domain, often failing to separate the effects of masks from concurrent interventions. More studies found that masks (n = 39/48; 81%) and mask mandates (n = 16/18; 89%) reduced infection than found no effect (n = 8/66; 12%) or favoured controls (n = 2/66; 3%). Seven observational studies found that respirators were more protective than surgical masks, while five found no statistically significant difference between the two mask types. Despite the ROB, and allowing for uncertain and variable efficacy, we conclude that wearing masks, wearing higher quality masks (respirators), and mask mandates generally reduced SARS-CoV-2 transmission in these study populations.This article is part of the theme issue 'The effectiveness of non-pharmaceutical interventions on the Covid-19 pandemic: the evidence'.

本项快速系统证据综述旨在探究以下三个问题：（1）佩戴口罩能否降低严重急性呼吸综合征冠状病毒2（SARS-CoV-2）的传播；（2）不同类型口罩的防护效果是否存在差异；（3）强制口罩政策是否可减少病毒传播，研究场景涵盖社区环境与医疗场所。本研究检索了2020年1月1日至2023年1月27日发表的相关研究，共获得5185条独立记录。由于随机对照试验（randomized controlled trial, RCT）数量匮乏，本次分析纳入了观察性研究。我们共分析了35项社区环境相关研究（含3项RCT与32项观察性研究），以及40项医疗环境相关研究（含1项RCT与39项观察性研究）。纳入的研究中，95%是在高传染性奥密克戎变异株出现之前开展的。91%的观察性研究至少在一个领域存在“严重”偏倚风险（risk of bias, ROB），通常无法区分口罩干预与同期其他干预措施的独立效果。更多研究显示，口罩使用（n = 39/48; 81%）与口罩强制令政策（n = 16/18; 89%）可降低感染风险，仅少数研究认为口罩使用无效果（n = 8/66; 12%）或对对照组存在偏向性（n = 2/66; 3%）。7项观察性研究发现，防护口罩（respirators）的防护效果优于医用外科口罩，另有5项研究未发现两种口罩类型间存在统计学显著差异。尽管存在偏倚风险，且需考虑口罩防护功效存在不确定性与变异性，我们仍得出结论：佩戴口罩、使用更高防护等级的防护口罩以及实施口罩强制令政策，在本次研究纳入的人群中总体上可降低SARS-CoV-2的传播。本文隶属于期刊主题专刊《非药物干预措施对新冠大流行的有效性：证据》。