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

We estimate that in the first wave of inter-country spread not including mainland China the countries at highest risk are still mainly within Asia, the Pacific, North America and Europe. The first importations of cases to and from countries outside mainland China have already occurred, including from Singapore to the UK, 23 and Thailand, Japan and Singapore to the South Korea. 12 Singapore was second highest on our UK donor risk result list after Hong Kong and Japan, Singapore and Thailand were numbers 4, 5 and 6 on the South Korea's list after Macao, Hong Kong and Taiwan. Given our results and these observations, it would seem prudent for planning to consider the scenario in which the number of countries that may be both recipient and donors of importations will be increasing. Once transmission is confirmed in a possible donor country, our estimates of the risk transmission index are no longer needed, and the number of reported cases and the volume of traffic between countries are what will become important (see Table S3 ). However it must be considered that transmission may not always be detected quickly in all possible donor countries so estimates of the risk of transmission in donor countries may remain useful for planning. Though many of the countries at risk of second wave importations are similar to those at risk from Wuhan, there are some countries that we did not estimate as having the highest numbers of importations from Wuhan, but become at increased risk as we consider donor countries outside mainland China. These include India, New Zealand, Spain and Mexico, as they have greater links to countries outside mainland China than to Wuhan, China. With the first imported case in Africa recently reported in Egypt 24 (which was estimated to have the highest link with mainland China by Lai et al. 8 ,) we must assess where we are in the timeline of the outbreak with respect to importations to Africa, and including the risk of importation from not only mainland China could be important here.