Reconstruction of the full transmission dynamics of COVID-19 in Wuhan

Abstract

As countries in the world review interventions for containing the COVID-19 pandemic, important lessons can be drawn by studying the full transmission dynamics of SARS-CoV-2 in Wuhan, China, where vigorous non-pharmaceutical interventions have largely suppressed the local COVID-19 outbreak. Here, we use a modelling approach to reconstruct the full-spectrum dynamics of COVID-19 between December 8 2019 and March 8 2020 across five phases marked by events and interventions on the basis of 32,583 laboratory-confirmed cases. Accounting for presymptomatic infectiousness, time-varying ascertainment rates, transmission rates and population movements, we identify two key features of the outbreak: 87% (lower bound 53%) of the infections were unascertained, potentially including asymptomatic, presymptomatic, and mild-symptomatic cases; and a basic reproduction number R_0 much higher than for SARS and MERS, with our estimates indicating a value of 3.54 (95% credible interval: 3.41-3.66) in the early outbreak. We observe that multi-pronged interventions had considerable positive effects on controlling the outbreak, decreasing the reproduction number to 0.27 (0.23-0.32) and by projection reducing the total infections in Wuhan by 96.1% as of March 8. We furthermore explored the probability of resurgence following lifting of interventions after 14 days of no ascertained infections, estimating it at 0.33 and 0.06 based on models with 87% and 53% unascertained infections, respectively, highlighting the risk posed by unascertained cases in changing intervention strategies. These results provide important implications for continuing surveillance and interventions to eventually contain COVID-19 outbreaks.