Measuring imported case risk of COVID-19 from inbound international flights --- A case study on China

Abstract

With COVID-19 spreading around the world, many countries are exposed to the imported case risk from inbound international flights. Several governments issued restrictions on inbound flights to mitigate such risk. But with the pandemic controlled in many countries, some decide to reopen the economy by relaxing the international air travel bans. As the virus has still been prevailing in many regions, this relaxation raises the alarm to import overseas cases and results in the revival of local pandemic. This study proposes a risk index to measure one country's imported case risk from inbound international flights. The index combines both daily dynamic international air connectivity data and the updated global COVID-19 data. It can measure the risk at the country, province and even specific route level. The proposed index was applied to China, which is the first country to experience and control COVID-19 pandemic while later becoming exposed to high imported case risk after the epidemic centers switched to Europe and the US afterward. The calculated risk indexes for each Chinese province or region show both spatial and temporal patterns from January to April 2020. It is found that China's strict restriction on inbound flights since March 26 was very effective to cut the imported case risk by half than doing nothing. But the overall index level kept rising because of the deteriorating pandemic conditions around the world. Hong Kong and Taiwan are the regions facing the highest imported case risk due to their superior international air connectivity and looser restriction on inbound flights. Shandong Province had the highest risk in February and early March due to its well-developed air connectivity with South Korea and Japan when the pandemic peaked in these two countries. Since mid-March, the imported case risk from Europe and the US dramatically increased. Last, we discuss policy implications for the relevant stakeholders to use our index to dynamically adjust the international air travel restrictions. This risk index can also be applied to other contexts and countries to relax restrictions on particular low-risk routes while still restricting the high-risk ones. This would balance the essential air travels need and the requirement to minimize the imported case risk.

Keywords: COVID-19; China; Imported case risk; International air travel.

Fig. 1

Evolution of $A{c}_i^n$, $A{q}_i^n$ and $A{m}_i^n$ of the US.

Fig. 2

Evolution of China's imported case risk index, reported number of imported cases and the number of inbound international flights.

Fig. 3

The number of existing confirmed cases in major regions around the world. Note: we use the different y (vertical)-axis (on the right-hand side) for Iran and the US in Fig. 3(a) and (b) respectively, as these two countries experienced much faster confirmed cases growth than other countries. Such treatment makes the figures to exhibit more clearly.

Fig. 4

The comparison of China's overall imported case risk with and without the inbound flight cut policy.

Fig. 5

Visualization of each province's risk index in February 2020.

Fig. 6

Visualization of each province's risk index in March 2020.

Fig. 7

Visualization of each province's risk index in April 2020.

Fig. 8

Evolution of daily confirmed cases for major countries imposing the risk of imported cases for China.

Fig. 9

Change of international air connectivity for major countries.