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

We next applied the system to the observed outbreak before the travel restrictions of January 23 -a total of 811 documented cases throughout China. Figure 1 shows simulations of reported cases generated using the best-fitting model parameter estimates. The distribution of these stochastic simulations captures the range of observed cases well. In addition, the best-fitting model captures the spread of COVID-19 to other cities in China ( Figure S9 ). Our median estimate of the overall 4 is 2.23 (95% CI: 1.77−3.00), indicating a high capacity for sustained transmission of COVID-19 (Table 1) . This finding aligns with other recent estimates of the reproductive number for this time period 6, [12] [13] [14] . In addition, the median estimates for the latent and infectious periods are approximately 3.77 and 3.45 days, respectively. Further, we find that, during January 10-23, only 14% (95% CI: 9-26%) of total infections in China were reported. This estimate reveals a very high rate of undocumented infections: 86%. This finding is independently corroborated by the infection rate among foreign nationals evacuated from Wuhan (see Supplementary Appendix). These undocumented infections are estimated to have been half as contagious per individual as reported infections (µ = 0.52; 95% CI: 0.44 -0.69). Other model fittings made using alternate values of ! and \X] produced similar parameter estimates ( Figure S10 ).