Estimating number of global importations of COVID-19 from Wuhan, risk of transmission outside mainland China and COVID-19 introduction index between countries outside mainland China

Haoyang Sun; Borame Lee Dickens; Mark Chen; Alex Richard Cook; Hannah Eleanor Clapham

To date, the reported total number of imported cases from Wuhan ( ) differ substantially between countries even after adjusting for the volumes of air passengers arriving from Wuhan. We assumed this was due to inter-country variation in case detection and reporting rates. We ranked countries based on the ratio between the reported case count and passenger volume → , , and assumed all the imported COVID-19 cases from Wuhan have been successfully detected and reported by countries having the top 10 rankings, to provide a conservative estimate for 0 and hence the number of cases imported from Wuhan to the rest of the countries we consider. In the equation below, Θ refers to the set of the aforementioned countries having the highest rankings, and the posterior of 0 follows a gamma distribution if we impose a uniform prior: