Widespread use of face masks in public may slow the spread of SARS CoV-2: an ecological study

Chris Kenyon

is the (which was not peer-reviewed) The copyright holder for this preprint . https: //doi.org/10.1101 //doi.org/10. /2020 In this ecological study we found that countries that promoted widespread face mask 185 usage had lower cumulative numbers of COVID-19 diagnosed after controlling for 186 testing intensity and age of the epidemic. It is important to note that this association 187 may be entirely explained by unmeasured confounders. For example, if countries 188 promoting universal face masking also conducted more effective contact tracing and 189 isolation than other countries and this was responsible for the slower spread, our 190 study design would have falsely attributed this effect to using face masks. We did not 191 have accurate data to control for these confounders. We did however control for 192 testing intensity which is an important potential confounder. We also controlled for 193 the age of the epidemic which is an obvious independent determinant of the size of 194 the epidemic. A further limitation of our study was that we were unable to quantitate CC-BY-NC-ND 4.0 International license It is made available under a author/funder, who has granted medRxiv a license to display the preprint in perpetuity.