A Case of ‘All-or-None’? The Impact of Airline Travel On The Precocity And Severity of Covid-19 In Sub-National Areas Across 46 Countries

Human travel fed the worldwide spread of Covid-19, but it remains unclear whether the volume of incoming air passengers and the centrality of airports in the global airline network made some regions more vulnerable to earlier and higher mortality. We assess whether the precocity and severity of Covid-19 deaths were contingent on these measures of air travel intensity, controlling for differences in local non-pharmaceutical interventions and pre-pandemic structural characteristics of 503 sub-national areas on five continents in April-July 2020. OLS models of precocity (i.e., the timing of the 1st and 10th death outbreaks) reveal that the volume of incoming passengers and the centrality of airports were not impactful once we controlled for local characteristics. We model severity (i.e., the weekly death incidence of Covid-19) with both GLMM and OLS regressions. Results suggest that death incidence was insensitive to the number of passengers and airport centrality, with no substantial changes over time. However, total travel bans did reduce mortality significantly. We conclude that Covid-19 importation through air travel followed an ‘All-or-None’ principle: it contributed to mortality at all times but not proportionally to the number of incoming passengers nor the position of airports in the global network of travel.