Future Tense

At Best, Travel Bans to Stop Infectious Diseases Merely Delay the Inevitable

A row of lanes, each beneath an electronic sign displaying a red X.
Empty check-in lanes at the entrance to the blockaded ferry terminal at the Port of Dover in England on Dec. 23. France and Britain reopened cross-Channel travel after a 48-hour ban to curb the spread of the new coronavirus variant B-117. Justin Tallis/Getty Images

From The Plague Cycle: The Unending War Between Humanity and Infectious Disease by Charles Kenny. Copyright © 2021 by Charles Kenny. Reprinted by permission of Scribner, an imprint of Simon & Schuster Inc.

Flu may kill far more people every year than Ebola ever has, but unless we give a new variant a new name (swine flu, as it might be), it doesn’t raise as much concern. This may help explain why a November 2014 survey in the U.S. ranked Ebola as the third most urgent health problem facing the country—just below the cost of health care and ahead of cancer and heart disease. That fear was accompanied by widespread calls for travel bans, even though there’d been only two cases of Ebola transmission inside the United States, neither of which were fatal, and all experts were saying there was little risk of spread.

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This exclusion instinct is based on evolutionary reality. Staying away from strangers is a rational reaction in the face of an unknown infectious threat. If it isn’t clear who is sick, the only strategy that works is to reduce contact with everyone.

Today, though, when most of the world lives in cities and only a small minority of the planet’s population is in any way self-sufficient when it comes to producing food (or anything else), total isolation simply isn’t an option. Testing and isolating the sick, along with tracing their contacts, was a successful strategy against Ebola in 2014 and against COVID-19 in 2020. “Social distancing” was a necessary but expensive fallback in 2020 when we didn’t know who was infected.

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Distancing and stay-at-home orders often worked to reduce the average number of people infected by each person with COVID-19 to below one, meaning that infection rates decreased. But an early estimate of the effects of the coronavirus lockdowns on the U.S. economy from just the one month of April 2020 suggests an average cost of $5,000 per household. (The effects were far larger for some families: More than 20 million people were thrown out of work in the U.S. during April alone.)

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And the associated health impacts of the early coronavirus response were considerable worldwide. Those with conditions other than COVID-19 were kept away from hospitals, routine immunization programs were paralyzed, and millions were sunk into poverty where they suffered from malnourishment and the illnesses that are its by-product. Early estimates suggested that in some developing countries the response to COVID-19 might kill more than the infection itself.

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Lockdowns were never designed to be a stand-alone solution. Rather, they were a short-term strategy to buy time for better strategies and to prevent hospitals from being overwhelmed by patients. And it’s worth repeating that people sensibly and instinctually want to stay away from others when there’s a new disease spreading with no cure. At the start of COVID-19’s spread, it didn’t take regulations from above for people to stop going to restaurants and cut back on shopping. But for whatever highly contagious, often asymptomatic novel infection that comes next, every country needs to be efficient at using the time provided by lockdowns to come up with less restrictive methods to slow spread and build confidence. Those methods should include mass testing and tracing that allows for selective isolation.

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Notably, exclusion at the border is far more expensive and far less effective in a world based on global exchange. Quarantines and border controls probably helped reduce the spread of plague, but they proved considerably less useful against cholera and yellow fever in the 19th century. Today, even while isolation of the individual sick tourist can be a practical emergency strategy, and short-term travel bans may sometimes have a role to buy extra time to respond to a new pandemic, the world is simply too connected for even the greatest build-a-wall fantasist to think diseases can long be kept out by closing borders.

In 1986, for example, AIDS was added to the list of infections that would prohibit permanent entry under the U.S. Immigration Act. Even tourists with HIV had to apply for a waiver that, if granted, involved an indelible stamp in their passport announcing to all their HIV status. This despite the fact that in 1987 the World Health Organization had concluded that screening or banning international travelers wasn’t an effective tool to reduce the HIV burden. You can tell that travel limits didn’t work to stop the spread of AIDS because it was first identified in the U.S. (rather than in the Congo Basin) and quickly reached the countries most cut off from international travel and commerce, including Burma under the junta.

Similarly, travel controls put in place over the H1N1 virus in 2009 led to a 40 percent drop in air traffic to and from Mexico following the international alert, but had no effect on the spread of the disease. Epidemiologist Paolo Bajardi and colleagues argue that the evidence from the H1N1 outbreak suggests that even a comprehensive travel ban would, at best, have delayed the spread of the condition by 20 days.

The limited efficacy of travel bans in the face of a frequently asymptomatic and rapidly spreading disease was on full display with COVID-19. While it’s good to avoid people congregating in airports or in airplanes as much as it is in trains or factories during efforts to reduce the spread of a disease, there’s no cross-country evidence that countries that introduced travel bans saw lower rates of coronavirus infection in the first few months of 2020. Early estimates of the overall impact of travel bans suggest they slowed the spread of the virus from between two to three weeks at maximum and zero days at minimum.

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The U.S. government issued its first partial travel restrictions on Jan. 31. In the time between the coronavirus emerging in China and the United States travel ban, 390,000 people flew from China to the U.S. There’s some evidence that COVID-19 may have spread during the Las Vegas Consumer Electronics Show between Jan. 7 and Jan. 10, attended by 170,000 people. There was a coronavirus case in the U.S. on Jan. 20. And there was at least one COVID-19 death in California on Feb. 6, suggesting an infection two weeks prior.

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Even in the two-month period after the U.S. travel ban was introduced, a further 40,000 people (including U.S. citizens and green card holders) made the journey from China to the U.S. Worldwide, between January and early April, nearly 11 million people flew into the U.S. from countries with confirmed cases of COVID-19. And the threat of wider travel bans meant that millions of people rushed home before they were enforced. That led to packed immigration and customs halls, crushing thousands of people together in a small space for many hours. Crowded terminals at JFK and Newark were likely a factor in the severity of the outbreak that hit New York City.

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It wasn’t just the U.S., of course: A French hospital treated someone for pneumonia at the end of December 2019. Blood taken at the time was later tested for COVID-19 and came back positive. France imposed a travel ban in mid-March. Something similar has played out with the new, more contagious B-117 coronavirus variant. It was first reported in the U.K., where it is believed to have originated, in mid-December, and soon after, countries began restricting travel for visitors from the U.K. But the variant may have been in the U.S. since October.

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For a globally connected country, there may have been some benefit from imposing travel restrictions in early January or before, but no government acted that early. The first government worldwide to put in place an international travel ban related to COVID-19 was the Marshall Islands. It was introduced on Jan. 24. (That said, small island nations are where short-term travel bans may make the most sense: New Zealand banned foreigners entering the country in mid-March 2020 when it had 28 confirmed cases of COVID-19 and put the whole country in lockdown soon thereafter. When that was combined with a vigorous test-trace-isolate strategy for suspected cases, the initial outbreak was rapidly controlled.)

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Worse, travel bans remained in place long beyond any hope of efficacy. U.S. bans were in place through the first half of 2020 despite the fact that the country had more confirmed cases of COVID-19 than any other for most of that time.

Banning travel usually simply complicates authorities’ response to new disease threats—slowing the arrival of staff, supplies, and equipment to the countries battling an outbreak. Trade and collaboration, the transfer of goods, people, and ideas, are central to supporting health systems as well as developing and rolling out tests, treatments, and cures. We cannot respond effectively alone. We have to respond collectively.

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And in the longer term, there are reasons to think travel bans may further increase risk: A 2006 study of HIV-positive travelers from the U.K. to the U.S. who were taking antiretroviral drugs at the time found that the majority traveled illegally rather than report their condition and risk either exclusion or exposure. Nearly one-fifth of those surveyed stopped or delayed taking their antiretroviral medicines for fear of being searched on arrival in the U.S. and their status being discovered. Not only did they increase their own health risks by doing so, given that antiretrovirals help reduce transmission of HIV; the suspension of self-treatment increased the risks to anyone they had sex with in the United States.

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Because of the importance of global connections to the quality of life, by far the largest economic cost of many recent global infectious threats, including COVID-19, has been the reaction of people and governments to the threat, rather than the disease itself. We’ve seen that the Black Death could kill off one-third of the European continent and the immediate social and economic effect was surprisingly limited. And in an age where travel and trade were a very minor component of the global economy, regulations governing the movement of goods and people were comparatively minor disruptions to local economies. When Dubrovnik, in what is now Croatia, was introducing the concept of quarantine to the world during the Black Death, global trade was a few percentage points of output at most.

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But the extent of global integration today explains why even fairly insignificant disease threats can have such outsize economic impact. SARS killed fewer than 800 people, for example, but the economic cost of the global response was $140 billion. A World Bank estimate from a few years ago of the global costs of a severe global pandemic on the scale of the 1918 flu was that it might equal 5 percent of global gross domestic product, or $3 trillion. COVID-19 quickly showed that estimate to be wildly optimistic.

And because we’re no longer in a Malthusian age, pandemics don’t even have the small silver lining of fostering equality. Research on epidemics over the past 20 years by economists at the International Monetary Fund suggests that poor people aren’t only more likely to die during an outbreak; they’re more likely to lose jobs and fall further behind the incomes of the rich.

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Long-term exclusion and border controls were always a partially effective response to disease threats, at best. Today, they’re simply unaffordable—significantly counterproductive for health, ruinous for quality of life. The only solution is to use the immense innovative power and production capabilities that a globally connected and urbanized world has bequeathed to develop and roll out more effective responses.

Future Tense is a partnership of Slate, New America, and Arizona State University that examines emerging technologies, public policy, and society.

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