Synchronized travel restrictions across cities can be effective in COVID-19 control

Haiyan Liu; Xuemei Bai; Huanfeng Shen; Xiaoping Pang; Zeyu Liang; Yue Liu

While the impact of the population outflow from Wuhan is well established, the impact of other mobility patterns on the epidemic trajectory has not been well understood. Local population mobility for a city includes both intra-city and inter-city patterns. The inter-city mobility can be categorized into three sources, i.e., from Wuhan, from Hubei province (excluding Wuhan), and from cities outside Hubei. As nearly two-thirds of population outflow from Wuhan flooded into other cities within Hubei Province 13 , it is important to consider the population outflow from Hubei (excluding Wuhan) as a potentially significant source of epidemic transmission risk after 23 January 17 . The intra-city population movement is also an essential factor -research shows cities that introduced pre-emptive intra-city movement restrictions have 33.3% fewer confirmed cases in the first week of the epidemic outbreak compared to those that started restrictions after the emerging of confirmed cases 6 , pointing to the importance of the timing of introducing these measures. For inter-city population movement among cities outside Hubei, which are restricted after the Wuhan lockdown, different studies hold inconsistent views. On the one hand, the implementation of inter-city travel restrictions cannot significantly reduce the number of confirmed cases during the first week of city outbreaks 6 ; on the other hand, the transmission model of COVID-19 cannot be accurately established without the inter-city connections 19 .