evidence: A study of the impact of national face mask laws on COVID-19 mortality in 44 countries with a combined population of nearly one billion people found that, over time, the increase in COVID-19 related deaths was significantly slower in countries that imposed mask laws compared to countries that did not. The study, appearing in the American Journal of Preventive Medicine, published by Elsevier, shows that masks provide a supplementary layer of protection that could prevent unnecessary COVID-19 deaths. "While several studies before this have looked at the impact of masks on COVID-19 cases, fewer studies were focused on whether mask wearing may reduce COVID-19 deaths, and no study had looked at the data across multiple countries," said lead investigator Sahar Motallebi, MD, MPH, from Malmo, Sweden. "The large sample of culturally diverse countries in this retrospective study covers a large population, giving us more evidence towards the life-saving potential of masks during the COVID-19 pandemic." [...] Twenty-seven countries with face mask policies and 17 countries without face mask policies, covering a combined population of nearly one billion people, were included in the study. Investigators looked at COVID-19 deaths between February 15, 2020, the date of the first confirmed death in the targeted countries, to May 31, 2020, when many countries began to lift gathering and movement restrictions. Ten relevant demographic, social, clinical and time-dependent factors were examined. Potential confounders between face mask policy and mortality reduction, such as non-pharmaceutical interventions, were identified.