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Background The unprecedented outbreak of 2019-nCoV pneumonia infection in Wuhan City caused global concern, the outflowing population from Wuhan was believed to be a main reason for the rapid and large-scale spread of the disease, so the government implemented a city closure measure to prevent its transmission considering the large amount of travelling before the Chinese New Year.Methods Based on the daily reported new cases and the population movement data between January 1 and 31, we examined the effects of population outflow from Wuhan on the geographical expansion of the infection in other provinces and cities of China, as well as the impacts of the city closure in Wuhan in different scenarios of closing dates. ResultsWe observed a significantly positive association between population movement and the number of the 2019-nCoV cases. The spatial distribution of cases per unit outflow population indicated that some areas with large outflow population might have been underestimated for the infection, such as Henan and Hunan provinces. Further analysis revealed that if the city closure policy was implemented two days earlier, 1420 (95% CI: 1059, 1833) cases could have been prevented, and if Downloaded from httpsA c c e p t e d M a n u s c r i p t 4 two days later, 1462 (95% CI: 1090, 1886) more cases would be possible. ConclusionsOur findings suggest that population movement might be one important trigger for the transmission of 2019-nCoV infection in China, and the policy of city closure is effective to control the epidemic.

16The outbreak of pneumonia caused by a novel coronavirus (2019-nCoV) in Wuhan 17City of China obtained global concern, the population outflow from Wuhan has 18 contributed to spatial expansion in other parts of China. We examined the effects of 19 population outflow from Wuhan on the 2019-nCoV transmission in other provinces 20 and cities of China, as well as the impacts of the city closure in Wuhan. We observed 21 a significantly positive association between population movement and the number of 22 cases. Further analysis revealed that if the city closure policy was implemented two 23 days earlier, 1420 (95% CI: 1059, 1833) cases could be prevented, and if two days 24 later, 1462 (95% CI: 1090, 1886) more cases would be possible. Our findings suggest 25 that population movement might be one important trigger of the 2019-nCoV infection 26 transmission in China, and the policy of city closure is effective to prevent the 27 epidemic. 28

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