Estimating COVID-19 outbreak risk through air travel

Abstract

Background

Substantial limitations have been imposed on passenger air travel to reduce transmission of SARS-CoV-2 between regions and countries. However, as case numbers decrease, air travel will gradually resume. We considered a future scenario in which case numbers are low and air travel returns to normal. Under that scenario, there will be a risk of outbreaks in locations worldwide due to imported cases. We estimated the risk of different locations acting as sources of future COVID-19 outbreaks elsewhere.

Methods

We use modelled global air travel data and population density estimates from locations worldwide to analyse the risk that 1364 airports are sources of future COVID-19 outbreaks. We use a probabilistic, branching-process based approach that considers the volume of air travelers between airports and the reproduction number at each location, accounting for local population density.

Results

Under the scenario we model, we identify airports in East Asia as having the highest risk of acting as sources of future outbreaks. Moreover, we investigate the locations most likely to cause outbreaks due to air travel in regions that are large and potentially vulnerable to outbreaks: India, Brazil and Africa. We find that outbreaks in India and Brazil are most likely to be seeded by individuals travelling from within those regions. We find that this is also true for less vulnerable regions, such as the United States, Europe, and China. However, outbreaks in Africa due to imported cases are instead most likely to be initiated by passengers travelling from outside the continent.

Conclusions

Variation in flight volumes and destination population densities create a non-uniform distribution of the risk that different airports pose of acting as the source of an outbreak. Accurate quantification of the spatial distribution of outbreak risk can therefore facilitate optimal allocation of resources for effective targeting of public health interventions.