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 diﬀerence-in-diﬀerences (DID) estimations to disentangle the lockdown eﬀect on human mobility reductions from other confounding eﬀects including panic eﬀect, virus eﬀect, and the Spring Festival eﬀect. We ﬁnd that the lockdown of Wuhan reduced inﬂow into Wuhan by 76.64%, outﬂows from Wuhan by 56.35%, and within-Wuhan movements by 54.15%. We also estimate the dynamic eﬀects of up to 22 lagged population inﬂows from Wuhan and other Hubei cities, the epicenter of the 2019-nCoV outbreak, on the destination cities’ new infection cases. We ﬁnd, using simulations with these estimates, that the lockdown of the city of Wuhan on January 23, 2020 contributed signiﬁcantly to reducing the total infection cases outside of Wuhan, even with the social distancing measures later imposed by other cities. We ﬁnd 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 ﬁnd 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 oﬃcially reported cases and our estimated “actual” cases narrows signiﬁcantly.