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

Using the best-fitting model ( To highlight further this impact of contagious, undocumented COVID-19 infections on overall transmission and reported case counts, we generated a set of hypothetical outbreaks using the best-fitting parameter estimates but with = 0, i.e. the undocumented infections are no longer contagious (Figure 2) . We find that without transmission from undocumented cases, reported infections during January 10-23 are reduced 66.4% across all of China and 64.0% in Wuhan. Further, there are fewer cities with more than 8 cumulative documented cases: only 1 city with more than 8 documented cases versus the 10 observed by January 23 (Figure 2 ). This finding indicates that contagious, undocumented infections facilitated the geographic spread of COVID-19 within China.