December 16, 2025 | News | Letter to the Editor PNAS
Migration fell during the pandemic, but not in the ways we think
MPIDR researcher publishes Letter to the Editor in PNAS
A recent PNAS study, Measuring global migration flows using online data, by Guanghua Chi, Guy J. Abel, Drew Johnston, Eugenia Giraudy, and Mike Bailey uses Facebook data to estimate monthly international migration flows worldwide. The authors report that global migration fell sharply during the COVID-19 pandemic, declining by an estimated 64 percent in 2020, driven in part by the imposition of border controls, before rebounding strongly in 2022. The study has attracted broad international attention, including coverage in The New York Times.
© iStockphoto.com / imaginima
In earlier work, Jordan Klein, Ingmar Weber, and Emilio Zagheni examined how COVID-19 travel restrictions affected migration using Facebook advertising data. Their 2024 article in Demography, Stop, in the Name of COVID! Using Social Media Data to Estimate the Effects of COVID-19-Related Travel Restrictions on Migration, analyzed changes in migrant population between February and June 2020. While simple models linked entry bans to short-term declines in migrant numbers, this picture changed once broader pandemic-related disruptions were taken into account. Under those conditions, countries that imposed travel bans experienced increases in migrant population, meaning that any reduction in inflows was outweighed by an even larger reduction in outflows.
© MPIDR
© MPIDR
Klein and Weber have now published a Letter to the Editor in PNAS that brings these findings into conversation with the work of Chi et al. The letter argues that focusing only on total migration flows can obscure the mechanisms through which crisis-era policies operate.
“The COVID-19 pandemic affected migration in directionally different ways,” says Jordan Klein. “Domestic restrictions mainly reduced inflows, while border closures often curtailed outflows, effectively stranding migrants and impeding return to countries of origin. Looking only at total migration flows risks missing these dynamics and any potential unintended consequences of disease-control policies.”
The authors emphasize that the global migration dataset introduced by Chi et al. offers exactly the temporal and directional detail needed to study these effects, and they encourage future work to distinguish explicitly between inflows and outflows when evaluating migration responses to major crises.
Letter to the Editor
Jordan D. Klein, Ingmar Weber: The COVID-19 pandemic had heterogeneous effects on migration dynamics in PNAS (2025); DOI:
10.1073/pnas.2529730122
References
G. Chi, G. J. Abel, D. Johnston, E. Giraudy, M. Bailey: Measuring global migration flows using online data in PNAS (2025); DOI: 10.1073/pnas.2409418122
Klein, J. D.; Weber, I. G.; Zagheni, E.:
Demography, 1–19. (2024)
