Human Mobility Restrictions and the Spread of the Novel Coronavirus (2019-nCoV) in China

We quantify the causal impact of human mobility restrictions, particularly the lockdown of the city of Wuhan on January 23, 2020, on the containment and delay of the spread of the Novel Coronavirus (2019-nCoV). We employ a set of di?erence-in-di?erences (DID) estimations to disentangle the lockdown e?ect on human mobility reductions from other confounding e?ects including panic e?ect, virus e?ect, and the Spring Festival e?ect. We ?nd that the lockdown of Wuhan reduced in?ow into Wuhan by 76.64%, out?ows from Wuhan by 56.35%, and within-Wuhan movements by 54.15%. We also estimate the dynamic e?ects of up to 22 lagged population in?ows from Wuhan and other Hubei cities, the epicenter of the 2019-nCoV outbreak, on the destination cities’ new infection cases. We ?nd, using simulations with these estimates, that the lockdown of the city of Wuhan on January 23, 2020 contributed signi?cantly to reducing the total infection cases outside of Wuhan, even with the social distancing measures later imposed by other cities. We ?nd that the COVID-19 cases would be 64.81% higher in the 347 Chinese cities outside Hubei province, and 52.64% higher in the 16 non-Wuhan cities inside Hubei, in the counterfactual world in which the city of Wuhan were not locked down from January 23, 2020. We also ?nd that there were substantial undocumented infection cases in the early days of the 2019-nCoV outbreak in Wuhan and other cities of Hubei province, but over time, the gap between the o?cially reported cases and our estimated “actual” cases narrows signi?cantly. We also ?nd evidence that enhanced social distancing policies in the 63 Chinese cities outside Hubei province are e?ective in reducing the impact of population in?ows from the epi-center cities in Hubei province on the spread of 2019-nCoV virus in the destination cities elsewhere.