A virus that knows no borders? Exposure to and restrictions of international travel and the global diffusion of COVID-19

"Closing borders is naive, the virus will come regardless" - this was the policy assumption that was repeatedly stated until mid-March by the WHO, the EU, as well as responsible authorities in Germany and other countries. Meanwhile, other states had started closing their borders to travellers from high-risk countries or to introduce mandatory quarantines. On 17 March, the EU did what it had previously argued against, and closed its borders to travellers from outside the EU and the Schengen Area. Germany, too, changed its line, and closed its borders to France, Switzerland, and Austria and on 18 March also to travellers from Italy. Who was right? Those who initially rejected travel restrictions as useless or those countries that decided to introduce them early on? Results from a global analysis of travel restrictions and cross-national differences in mortality rates as a result of the COVID-19 pandemic suggest that the belief that the spread of the virus could not be significantly slowed down by entry restrictions was fatally mistaken. The paper also shows that exposure of a country to international travel, as indicated by centrality in air travel networks and tourist numbers is strongly associated with higher COVID-19 mortality rates. By contrast, island states, which have lower exposure to international travel because of their lack of land borders, have much lower mortality. The results are robust across a wide variety of model specifications and controls, including domestic COVID-19 containment measures. The findings have important policy implications and suggest that in containing upcoming waves of the COVID-19 pandemic as well as similar pandemics in the future, the risks of exposure to international travel and the advantages of early travel restrictions should be given much greater weight. Among various types of travel restrictions, the findings suggest prioritizing targeted restrictions over global ones, and mandatory quarantines for travellers over entry bans.