The team of authors studied the impact of large-scale anti-contagion interventions designed to slow the spread of COVID-19 in six countries where early spread of the virus triggered policy deployments (China, South Korea, Italy, Iran, France, and the US). The choice of countries analyzed was also motivated by the diversity of the team in terms of nationalities represented and languages spoken. The authors collected and publicly released a new dataset consisting of 1,717 anti-contagion policies (including social distancing measures, school closures, travel restrictions, and lockdowns) implemented between January and April 2020 at the national, regional, and local level; and also subnational epidemiological case data.
The research found that in the absence of policy intervention, the number of COVID-19 infections was doubling approximately every two days. These combined policies have substantially flattened the curve. The authors estimate that together these policies averted or delayed roughly 60 million confirmed cases, and 500 million total infections (accounting for under-detection) as of the beginning of April in the six countries studied.