In a pandemic, migration from densely populated cities is more effective than closing borders

WASHINGTON, November 17, 2020 – Pandemics are fueled, in part, by a dense population in large cities where networks of buildings, crowded sidewalks, and public transportation are forcing people into stricter conditions. This contrasts with the conditions in rural areas, where there is more space available per person.

According to common sense, being in less crowded areas during a pandemic is safer. But even the mayors of small towns want to protect people, and the migration of people from cities to rural towns brings concerns. During the COVID-19 pandemic, closure of national borders and borders between states and regions was prevalent. But does it really help?

In an article published in Chaos, curated by AIP Publishing, two researchers decided to test this hypothesis and find out if imprisonment and travel bans are really effective ways to limit the spread of a pandemic disease. In particular, they focused on the movement of people from larger to smaller cities and tested the results of this one-way migration.

“Instead of taking mobility, or lack of mobility, for granted, we set out to explore how impaired mobility would affect diffusion,” said lead author Massimiliano Zanin. “The real answer lies in the sign of the result. People always take it for granted that closing borders is good. We have found that it is almost always negative.”

The model used by the authors is simplified, without many of the details influencing migration patterns and disease spread. But their attention to changes in population density indicates that travel bans may be less effective than migrating people to less dense areas. The result was a reduced spread of the disease.

Zanin and collaborator David Papo placed a hypothetical group of people in two places and assumed their journey was in random movement patterns. They used SIR dynamics, which is common in epidemiological studies of disease movement. SIR stands for susceptible, infected and recovered: classifications used to label groups in a simulation and monitor the spread of the disease based on their interactions.

They ran 10,000 iterations of the simulation to determine the subsequent spread of the disease between people in two locations when migration is one-way: from dense to less dense cities. They also studied the effect of “forced migration”, which moves healthy people out of densely populated cities at the start of a pandemic.

The results showed that while movement from large cities to small cities may be slightly less safe for people in small cities, overall for a global pandemic situation, this reduction in the density of highly populated areas is better for most of people.

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“Collaboration between different governments and administrations is an essential ingredient in controlling a pandemic, and small-scale sacrifices should be considered to achieve global advantage,” Zanin said.

The article, “Travel Restrictions During Pandemics: A Helpful Strategy?” is written by Massimiliano Zanin and David Papo. The article will appear in Chaos on November 17, 2020 (DOI: 10.1063 / 5.0028091). After that date, it can be accessed at https: //aip.scitation.org /doi /10.1063 /5.0028091.

Chaos is dedicated to increasing understanding of nonlinear phenomena in all areas of science and engineering and describing their manifestations in a way understandable to researchers from a broad spectrum of disciplines. See https: //aip.scitation.org /magazine/no.