Relative risk of importing at least one novel coronavirus (COVID-19 / 2019-nCoV) case by country as of 31/01/2020
Najmul Haider, Alexei Yavlinsky, David Simons, Abdinasir Yusuf Osman, Francine Ntoumi, Alimuddin Zumla, Richard Kock
In press, Epidemiology and Infection, DOI: 10.1017/S0950268820000424



The map above shows the relative risk of importing at least one 2019-nCoV case by country as of 31/01/2020. For countries that have already reported 2019-nCoV cases, this is equivalent to the risk of importing at least one additional case.

Methods

We assume that there is a fixed pool of people travelling by air from China to other countries, and within this pool the passengers have different probabilities of being infected depending on which city they are flying from (this probability is defined as the outbreak size divided by the population size for that city). We use the FLIRT tool from EcoHealth Alliance to simulate passenger flows from four Chinese cities — Wuhan, Beijing, Shanghai and Guangzhou — and then use that to estimate how the above passenger pool is divided up between the destination countries. The resulting proportions become relative risk values.

Because these results are based on a simulation rather than actual passenger data, we do not get individual passenger numbers and thus do not estimate absolute risk values. The advantage of it being a simulation is that it takes into account passengers who transfer between flights, in addition to the passengers who take direct flights.

Results

We then use these relative risk values to rank countries. Of the countries that reported at least one 2019-nCoV case at the date of publication, 24 countries were in the top quartile, two in the third, one in the second and none in the first. So far, the only countries in sub-Saharan Africa that rank similarly to the countries that have reported at least one case are Ethiopia and South Africa. However, since neither country has reported confirmed cases, this is a quantified indication of where these countries stand in terms of importation risk relative to the rest of the world.

On the other hand, this analysis suggests the possibility of unreported cases in Indonesia, Turkey, Pakistan and Qatar*, as their risk values are similar to countries in the region that have reported multiple confirmed cases.

Limitations

This approach has a number of limitations. As the volume of air traffic or outbreak sizes change over time, the risk values will not be directly comparable across different timepoints. Additionally, we do not take into account travel by land or sea.

Updates

On 14/02/2020, Egypt declared the first confirmed COVID-19 case on the African continent. Egypt ranks amongst the top five countries in Africa according to our risk model. Based on the data from 31/01/2020, these countries, ordered by relative risk, are Ethiopia, South Africa, Egypt, Mauritius and Morocco.

More information

More details can be found in our manuscript published in Epidemiology and Infection:

Passengers’ destinations from China: Low risk of 2019-nCoV transmission into Africa and South America

New: explore how relative importation risks compare between countries. Drag the selection box in the mini chart on the right to zoom in on different parts of the ranked country list. Click anywhere in the mini chart to center the box on that region. Increase or decrease the size of the box by dragging the top or bottom handle up or down. Best viewed on a large screen. X axis: relative risk value as of 31/01/2020 (0: no risk, 1: absolute certainty).

Map code adapted from Micah Stubbs and chart code from mnoichl

*As of 15/02/2020, these countries have not reported confirmed novel coronavirus cases.