The effect of international travel on the spread of COVID‐19 in the United States

Abstract We examine the relationship between incoming international passengers and COVID‐19 cases and deaths during the pandemic's initial wave in the United States. We find passengers from Milan, Italy, the location of an early outbreak, were an important source of exposure, increasing the early spread of COVID‐19 in the United States. Cities that received more passengers from Milan during the first quarter of 2020 experienced more COVID‐19 cases during March 2020 than cities receiving fewer passengers from Milan. Concurrently, cities that received more passengers from China or Rome (the latter not experiencing a major outbreak until later in 2020), did not experience increased cases. These results show passengers from at least one foreign epicenter were an important source of exposure that increased COVID‐19 spread in the United States. Given Milan was a secondary hotspot, our results also illustrate the importance of a holistic view of international pandemic hotspots when considering corresponding travel policy.