Perusing some coronavirus transmission literature the other day, I came across a June 27, 2020 meta-analysis in The Lancet called “Physical distancing, face masks, and eye protection to prevent person-to-person transmission of SARS-CoV-2 and COVID-19: a systematic review and meta-analysis” by Chu et al. The paper puts together data from 216 studies on SARS, MERS, and SARS-CoV2 involving 25,697 patients. Table 2 has a nice summary of their findings. Physical distancing of 1m reduced transmission from 12.8% to 2.6% (82% reduction) with each additional meter reducing transmission approximately 2 fold. Face masks reduced transmission from 17.4% to 3.1% (85% reduction) with medical or surgical masks significantly reducing transmission, multi-layer masks being better than single layer masks, and N95 respirators probably reducing it even further. Eye protection (goggles or face shields), which the authors note is “typically unconsidered,” reduced transmission from 16% to 5.5% (66% reduction). With any study like this there are a lot of caveats, and certainly large scale, well conducted, randomized trials would be better, however, this is a good foundation upon which to base decision making. I’ve certainly added eye protection (tight fitting safety glasses in my case) to my distancing and multi-layer mask wearing since I read this paper. It is imprtant to note that face shields aren't a substitute for masks, but when used together appear to contribute to increased protection.