State of the Pandemic, Clinical Public Health, Asia, China
development

Period. 30 March – 5 April 2020

Substantial undocumented infection facilitates the rapid dissemination of COVID-19 (Li et al, Science)

Findings

Using a model-inference framework, the authors estimates the contagiousness and proportion of undocumented infections of COVID-19 in 375 cities in China before (Jan 10-23) and after (Jan 24-Feb 8) implementation of control measures in Wuhan (including: travel restrictions self-quarantine and contact precautions, access to rapid testing and PPE). The effective reproduction number (Re), i.e. number of secondary infections per index infection, was 2.4. The authors estimate that before control measures, 86% of all infections were undocumented, estimated to be about half (55%) as contagious as reported infections. After Control Measures, the proportion of undocumented infections fell to 31-35%, while the Re decreased to 0.99-1.4.

Interpretation

Although inference results should be interpreted with caution, the study suggests that control measures in Wuhan as of Jan 23 altered the epidemiological characteristics of the outbreak.

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