Once Covid-19 hits a country, it spreads. Epidemiological models predict diffusion based on how people move in normal times (i.e., in the past) or using real-time data. Both approaches have shortcomings. Economics can provide useful insights on the motives for people to move during a pandemic, and might therefore help address these shortcomings.
The key idea of this policy brief and its underlying research is that a key agent in the diffusion of the virus might be the internal migrant. Covid-19 hits first the biggest economic centres in a country, because they are more exposed to international trade, tourism and international migration. As the virus spreads in these economic centers, central governments shut down economic activities and ask people to stay home. These measures leave recently settled migrants jobless and socially isolated and therefore push them to go back to their home towns. By doing so, they spread the virus much further away from the outbreak than other models would predict. To a certain extent, internal migrants may become super-spreaders, not because of some medical condition, but because of their socio-economic condition.
This policy brief develops a methodology to identify, for a given country, which regions are more exposed to return migration than others and explains in detail what data are needed to calculate such exposure, so that anybody with access to subnational data on pre-Covid migration might calculate such index and therefore predict which regions have the highest risk. This methodology has been validated using Italy regional-daily data on Covid deaths and pre-Covid data on recently settled migrants. The findings suggest that the return migration mechanism exists and that it is quantitatively important, because it explains about 22-24 percent of Covid deaths outside outbreak areas.
Return migration is likely to be quantitatively important in many other countries, because i) internal migration to big cities is a common phenomenon around the world, and ii) big cities are likely to be hit by Covid-19 before any other areas of the country. Countries with important internal migration flows should make a ranking of the regions more exposed to return migration, design national lockdown policies taking such ranking into account, allocate more resources to more exposed regions, alert the corresponding local governments (who might be in the best position to track return migrants) and increase the intensity of persuasion campaigns reminding return migrants that they might be asymptomatic carriers of the virus.
The index and its validation might be particularly important for Muslim countries. As the end of the Ramadan approaches, millions of people prepare to migrate back to their home towns to celebrate Eid al-Fitr. It is hard to over-stress how such return migration might result in a health disaster.
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