Substantial undocumented infection facilitates the rapid dissemination of novel coronavirus (COVID-19)

Ruiyun Li; Sen Pei; Bin Chen; Yimeng Song; Tao Zhang; Wan Yang; Jeffrey Shaman

Daily numbers of travelers between 375 Chinese cities during the Spring Festival period ("Chunyun") were derived from human mobility data collected by the Tencent Location-based Service (LBS) during the 2018 Chunyun period (February 1 -March 12, 2018) 8 . Chunyun is a period of 40 days -15 days before and 25 days after the Lunar New Year -during which there are high rates of travel within China. To estimate human mobility during the 2020 Chunyun period, which began January 10, we aligned the 2018 Tencent data based on relative timing to the Spring Festival. For example, we used mobility data from February 1, 2018 to represent human movement on January 10, 2020, as these days were similarly distant from the Lunar New Year. During the 2018 Chunyun, a total of 1.73 billion travel events were captured in the Tencent data; whereas 2.97 billions trips are reported 8 . To reconcile these two numbers, we include the parameter in the model system.