The authors were interested in the prevalence and contagiousness of undocumented SARS-CoV-2 infections to understand the overall prevalence and pandemic potential of COVID-19. They used observations of reported infection within China together with mobility data to create a networked dynamic metapopulation model. This allowed them to infer critical epidemiological characteristics associated with SARS-CoV-2, including the fraction of undocumented infections and their contagiousness. The authors estimated that 86% of all infections were undocumented prior to the 23rd January 2020 travel restrictions. Per person, the transmission rate of undocumented infections was 55% of documented infections but, due to their greater numbers, undocumented infections were the infection source for 79% of documented cases. Therefore the virus was able to rapidly spread geographically, making its initial containment challenging.
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