Li et al, 2020. Substantial undocumented infection facilitates rapid dissemination

A modeling study using data from China estimated that in around 80% of all confirmed cases of covid-19 infection, the infection was acquired from a person who had an undocumented infection. Overall, around 86% of infections were undocumented. A high number of people with undocumented infections, many of whom were likely not severely symptomatic, appears to have facilitated the rapid spread of the virus throughout China.