The authors were interested in how the interventions used in China, such as travel restrictions, affected COVID-19 spread. They used real-time mobility data from Wuhan together with detailed case data, including travel history, to understand the role of case importation on transmission in cities across China. They found that, early on, the spatial distribution of COVID-19 cases in China was explained well by human mobility data. Once control measures were implemented, this correlation dropped and growth rates became negative in most locations. However, there were shifts in the demographics of reported cases, suggesting local chains of transmission still occurring outside Wuhan. Therefore the drastic control measures implemented in China did substantially mitigate the spread of COVID-19.
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