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

Abstract

Background The emergence of a novel coronavirus (SARS-CoV-2) in Wuhan, China in early December 2019 has caused widespread transmission within the country, with over 1,000 deaths reported to date. Other countries have since reported coronavirus disease 2019 (COVID-19) importation from China, with some experiencing local transmission and even case importation from countries outside China. We aim to estimate the number of cases imported from Wuhan to each country or territory outside mainland China, and with these estimates assess the risk of onward local transmission and the relative potential of case importation between countries outside China. Methods We used the reported number of cases imported from Wuhan and flight data to generate an uncertainty distribution for the estimated number of imported cases from Wuhan to each location outside mainland China. This uncertainty was propagated to quantify the local outbreak risk using a branching process model. A COVID-19 introduction index was derived for each pair of donor and recipient countries, accounting for the local outbreak risk in the donor country and the between-country connectivity. Results We identified 13 countries or territories outside mainland China that may have under-detected COVID-19 importation from Wuhan, such as Thailand and Indonesia. In addition, 16 countries had a local outbreak risk estimate exceeding 50%, including four outside Asia. The COVID-19 introduction index highlights potential locations outside mainland China from which cases may be imported to each recipient country. Conclusions As SARS-CoV-2 continues to spread globally, more epicentres may emerge outside China. Hence, it is important for countries to remain alert for the possibilities of viral introduction from other countries outside China, even before local transmission in a source country becomes known.