Study: Travel Bans Won’t Thwart the Next Pandemic

The U.S. side of the border with Canada, near Seattle, which was closed for nonessential travel in March. 

Photographer: Mert Alper Dervis/Anadolu Agency via Getty Images

One of the earliest policy responses to the arrival of Covid-19 in the U.S. was to restrict international movement. In February, the Trump administration announced restrictions on travelers from China. Then Europe and Iran. In March, the Northern and Southern borders were partially closed; categorical bans were put in place on asylum seekers, and then on people moving to the U.S. for work or to be with family.

And while travel bans were a particular emphasis for the Trump administration, it wasn’t just the U.S. that favored this approach. Some 179 countries implemented emergency restrictions. 

As we enter a second year of pandemic, some travel restrictions that started out as temporary have been extended indefinitely. And some economists are asking whether it’s worth putting the brakes on global movement more permanently. A new working paper examines pandemics between 1889 and 2009 and finds no support for that approach.

The researchers from the Center for Global Development looked at four past pandemics and found that the level of movement before a pandemic hit did not significantly slow the spread of those diseases, and made almost no impact on deaths that ultimately resulted. 

While this study does not look directly at the ongoing coronavirus pandemic, the authors use the data on past pandemics to show how disease outbreaks spread relative to travel — and to provide insights about future outbreaks. Applying their findings to Covid-19 would mean that even if substantially fewer people were coming to the U.S. in December 2019, it would not have delayed the arrival of this pandemic by that much — and would have little to no effect on the number of people who ultimately die in the U.S. from the coronavirus. 

That’s likely because as long as any number of people travel across borders, it’s just a matter of time before they bring a communicable disease with them. “The risk that a pandemic arrives at any given moment of time is not like the risk of an accident when you’re driving a car — the faster you’re driving, the riskier it is,” says Michael Clemens, a senior fellow at CGD, and a co-author of the paper along with Thomas Ginn. Instead, it’s a fixed risk: It exists If you drive at all. As long as a critical mass of people are moving across borders, it becomes “almost certain” that the virus will follow, regardless of the reduction in numbers of travelers, Clemens explains. And once the virus is in a particular country, it is spread primarily by people within that country. 

“Once the epidemic has arrived and starts taking off, the greatest risk to anybody who is not infected or getting infected is from other people in the country, not from new travelers,” Clemens adds. “There should be barely any relation between the flow of people across borders and the eventual number of people who are sickened or killed by the pandemic.”

This paper didn’t analyze the Covid-19 emergency travel limits imposed after the arrival of the virus. Its focus, instead, is whether the level of travel between countries before a pandemic even starts makes a difference to how it spreads. 

In the paper, the researchers were looking to answer two key questions: First, if the rate of movement between countries slows before the outbreak of a global pandemic, does it substantially delay the virus’s arrival? And if there is a delay, how does that affect the deaths that ultimately result from the spread of disease?  

For answers, the researchers analyze data on four historic influenza pandemics: The “Russian flu” of 1189, the “Spanish flu” of 1918, the “Asian flu” of 1957 and the “swine flu” of 2009. They chose these, in part, because they had sufficient data for a robust analysis. They found that while the speed of international travel increased more than tenfold between 1889 and 2009, the pandemics differed by only six weeks in reaching most of the world’s population. 

Even with a drastic 50% reduction in international mobility before the pandemic, the delay in the arrival of the disease was only one to two weeks and there was “no detectable reduction in final mortality.” 

In theory, it is still possible that a nation could use the delay in the outbreak to enact measures that save lives, but it would already have to be quite cut off from international migration to begin with. In the real world, Clemens says it would be hard to envision a few weeks’ delay being a decisive factor in pandemic control.

To shave off even the tiny bit of what is admittedly a very salient risk from emergent diseases, we’d have to “eliminate the vast majority of all international movement, which would be so costly that it is difficult to see that making anybody better off,” Clemens says. 

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