Transmissibility of coronavirus disease 2019 (COVID-19) in Chinese cities with different transmission dynamics of imported cases
Abstract
Background
Monitoring the time-varying reproduction number ( R t ) of the disease is useful in determining whether there is sustained transmission in a population. In this study, we examined R t of COVID-19 and compared its transmissibility between different intervention periods in Hangzhou and Shenzhen.
Methods
Daily aggregated counts of confirmed imported and local cases between January 1, 2020 and March 13, 2020 were analysed. A likelihood function was constructed to estimate R t , accounting for imported cases.
Results
Although Hangzhou had fewer number of cases than Shenzhen, Shenzhen had higher proportion of imported cases than Hangzhou (83% vs 29%). Since the epidemic of COVID-19 in Shenzhen was dominated by imported cases, R t was kept below unity through time. On the contrary, R t was greater than unity in Hangzhou from 16 January to 7 February due to the surge in local cases. Credits to the Wuhan lockdown and outbreak response measures following the local lockdown, R t decreased steadily and dropped below unity in mid-February.
Conclusion
The lockdown measures and local outbreak responses helped reduce the potential of local transmission in Hangzhou and Shenzhen. Meanwhile, cities with similar epidemic trend could have different transmission dynamics given the variation in imported cases.
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