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01 april 2020

Substantial undocumented infection facilitates the rapid dissemination of novel coronavirus (SARS-CoV2) - Science

Bron: 16 March 2020: https://science.sciencemag.org/content/early/2020/03/24/science.abb3221
By R. Li et al.

To estimate the fraction of undocumented but infectious cases among 375 Chinese cities in a mathematical model


  • 86.2% (95% CI: 81.5%–89.8%) of all infections were infected from undocumented cases (without major restrictions or control)
  • Estimations indicate that government control efforts and population awareness have reduced the rate of spread of the virus, increased the reporting rate, and lessened the burden on already over-extended healthcare system;
  • Estimations could shift differently in other countries with different control, surveillance and reporting practices;
  • Identification and isolation of currently undocumented infections would be needed to fully control COVID-19.


  • Results for 10–23 January 2020 delineate the characteristics of COVID-19 moving through China without major restrictions or control, vs results for 24 January–3 February and 24 January–8 February with control efforts.
  • Using a mathematical model that simulates the spatiotemporal dynamics of infections among 375 Chinese cities
  • In the mathematical model:
    • Observed infections, and undocumented infections, with separate rates of transmission
    • Spatial spread: daily number of people traveling between city j to city i and a multiplicative factor (to compensate for underreporting and reconcile)
    • For each city: Si, Ei, Ii,r, Ii,i: the susceptible, exposed, documented infected, and undocumented infected sub-populations in city i
    • Z = the average latent period, D = the average duration of infection, μ = the transmission reduction factor for undocumented infections, β the transmission rate for documented infections, α = the fraction of documented infections, θ = the travel multiplicative factor
  • Results: 86% of infections went undocumented and that, per person, these undocumented infections were 55% as contagious as documented infections
  • Comparing before and after government control efforts: Reduced rate of spread of the virus (1.12 to 0.35 days-1), increased reporting rate (14% to 69%), and decreased burden on already over-extended healthcare system
  • Estimations could shift differently in other countries with different control, surveillance and reporting practices.