ABSTRACT
Background: Imported COVID-19 cases are a serious public health problem worldwide. However, limited epidemiologic information of imported cases affects the choice of prevention and control strategies.Methods: In this study, we collected data from 22 January 2020 to 21 April 2020 related to imported COVID-19 cases in Mainland China from the daily public data of the National Health Commission and the provincial health commissions.Findings: A total of 1610 cases of COVID-19 were imported from 49 countries and regions to 27 provincial administrative regions. 79.81% cases were imported from European countries and the United States. Before 29 March, the imported cases were mainly from the United States (27.66%) and United Kingdom (42.55%). After 29 March 2020, the daily newly imported cases from Russia rapidly growed. After 12 April, the number of daily newly imported cases gradually decreased and remained at a low level (12±7 cases per day). Airport entry was encouraged and ground crossing entry was limited with the help of dynamic surveillance of the weekly proportion of confirmed cases at ports. 54.04% imported confirmed cases were in the asymptomatic incubation period on arrival in Mainland China. The compulsory centralized quarantine decreased the risk of onward transmission from imported cases compared to home quarantine ( P <0.05).Interpretation: Prevention and control strategies based on the epidemiological characteristics of imported cases effectively protected Mainland China against reintroduction of the virus and re-initiation of the epidemic when the epidemic was still in a surge worldwide. Such measures included: exit screening, entry screening, and compulsory centralized quarantine of all inbound travelers followed by strict contact tracing. The experiences from Mainland China provide an example of effective measures to reduce transmission of imported COVID-19 cases.Funding Statement: Shanghai Science and Technology Commission, Pudong Health Bureau of Shanghai and Krebsliga Schweiz, BIL KFS. Declaration of Interests: None to be declared.