twitter share facebook share 2020-05-18 1140

If the novel coronavirus pandemic were turned into a movie, a pivotal scene would capture the unforgettable events of Saturday, March 14, at Chicago’s O’Hare International Airport. Three days prior, U.S. President Donald Trump had suddenly announced sweeping travel restrictions on most European countries that would go into effect at midnight on Friday, March 13. Although the travel ban was intended to apply only to foreigners, Trump declared on national television that he was “suspending all travel from Europe to the United States,” prompting thousands of panicked Americans to cut short their vacations and business trips and rush back to the United States. Spilling into packed arrival halls, they found themselves shoulder-to-shoulder in nearly motionless customs and immigration lines, healthy travelers sharing the stale air with those who had picked up the virus, some of whom were sweating and coughing. Social media posts from O’Hare showed a seething human mass of contagion as far as the eye could see.

Travelers waited in this tight-packed mob for as long as seven hours before they were “screened”—given a rudimentary questionnaire asking if they felt any symptoms or had been in contact with people known to be infected with the virus. Then most of them were allowed to return to their homes and communities, reportedly without clear instructions to self-isolate or quarantine. Similar scenes played out in at least a dozen other U.S. airports that day. There is no way to know for sure, since the United States had not—and still has not—organized adequate testing or contact tracing, but the airport rush of March 14 may well have set the United States on course to become the most COVID-19-infected country in the world.

The events of that Saturday were not the result of open borders or free movement. Rather, they were a consequence of slamming the border shut with little warning. Officials at the state level had no chance to prepare for the influx of arrivals. For two days after Trump’s announcement, most returning Americans, healthy or otherwise, passed through U.S. airports without being screened or receiving any quarantine information. Rudimentary screening procedures were finally organized on Saturday, the same day the ban on European travelers was implemented, but their primary effect was to cause dangerous bottlenecks. “You could hardly invent a better scenario for superspreading events,” Jeremy Konyndyk, the former director of USAID’s Office of U.S. Foreign Disaster Assistance, tweeted after seeing the images of stranded travelers. “Any cases of COVID in these crowds will have a far higher chance of spreading to others in these lines than if they were just allowed in unchecked.”

By suddenly halting travel from Europe, the Trump administration ignored a timeless lesson of human migration: slamming borders shut usually has the opposite of the intended effect. Rather than ending cross-border movement, sudden immigration bans or caps create large and often unmanageable rushes of people hoping to make it across the border before it is too late. These surges occur immediately after bans are announced, when returning travelers rush to meet real or imagined deadlines, and often in the days and weeks beforehand, in anticipation of expected announcements. And when some of the people rushing to cross the border are carrying a potentially deadly virus, the result can be catastrophic.


Travel bans and border closures do little to halt the spread of infectious diseases even when they are implemented with sufficient notice and preparation. One study conducted during the 2014 Ebola crisis in West Africa and published in the Harvard Public Health Review found that flight bans and border closures were “ineffective” in controlling the spread of the disease and sometimes made fighting the pandemic more difficult. Another study published this year in the Annals of Internal Medicine examined outbreaks of Ebola, MERS, and SARS and found that travel restrictions had only a “limited effect.” Such restrictions reduced new cases by three percent or less and ultimately failed to prevent outbreaks from spreading to new regions. And a study published by Science examined the spread of COVID-19 from Wuhan to other parts of China and to other countries and found that even near-total international travel restrictions have only a “modest” effect if the disease is still spreading rapidly within the source country.

When travel restrictions are hasty and haphazard, they aren’t just ineffective—they can be counterproductive. The Trump administration was not alone in learning this lesson the hard way during the current pandemic. On March 16, Canadian Prime Minister Justin Trudeau closed his country’s border with the United States to all but essential business traffic and called on Canadians traveling abroad to come home immediately. The following week, more than a million Canadians returned, many from spring-break vacations in Florida, which at that time had among the highest number of confirmed COVID-19 cases in the United States.

Canada was unprepared for the influx. Although Trudeau’s government asked returning travelers to self-quarantine for two weeks, it had no comprehensive system for enforcing this guideline or monitoring returnees. In at least some cases, border officials at overcapacity airports reportedly failed to deliver clear quarantine instructions. Many older “snowbird” couples were reprimanded by shopkeepers, neighbors, and fellow travelers for visibly ignoring the directive. One quarantine-flouting traveler who returned from abroad to the province of Newfoundland managed to infect 44 people with COVID-19 in a single visit to a funeral home. But it wasn’t until March 25, long after the border-closure rush had subsided, that Canada invoked its Quarantine Act and made it illegal for returning travelers to leave their homes for two weeks. By then, people returning home from abroad had seeded outbreaks of coronavirus across Canada: in Toronto, the number of daily cases nearly quadrupled by the end of the month, a rise health authorities attributed to spring-break returnees. Quebec was soon recording as many as 590 new cases a day as a direct result of people returning from the United States. It later emerged that nearly all of Canada’s initial COVID-19 infections came from the United States.

Internal travel bans caused similarly dangerous stampedes in some European countries. Italian Prime Minister Giuseppe Conte’s March 8 decision to lock down the entire country and ban intercity travel caused a large-scale rush to train stations in Milan and other northern cities, where packed trains carried thousands of people, many of whom were infected, to southern regions, where authorities were unprepared to monitor or quarantine them. Anticipation of Conte’s announcement “caused many people to try to escape, causing the opposite effect of what the decree is trying to achieve,” Milan virologist Roberto Burioni told The Guardian. A week later in France, the sudden imposition of internal travel restrictions sparked a similar exodus from Paris to less-infected peripheral regions, where officials struggled to enforce quarantines; one phone-tracking study found that a million Parisians fled the capital on tightly packed trains.

When it comes to beat-the-ban border rushes, however, the United States is in a league of its own. Trump has made sudden border closures his signature coronavirus policy. The first one came on January 31, when he banned foreign nationals from entering the United States if they had been to China in the previous two weeks. By that point, more than 400,000 people had already flown to the United States from China, including thousands directly from Wuhan, in the four weeks since the coronavirus outbreak had come to the attention of U.S. authorities. Many of these people had rushed home in anticipation of a travel ban—or in the two-day period between the president’s announcement and when the ban went into effect.

The ban had another flaw. Like all border closures, this one necessarily exempted U.S. citizens, as well as green-card holders and their relatives. According to The New York Times, almost 40,000 people arrived in the United States on direct flights from China during the eight weeks after the ban went into effect. An even larger number may have arrived from China via connecting flights. And until mid-March, many of these people received no screening or quarantine instructions.

Trump’s March 14 ban on European travel was even more disastrous. The crowds that descended on U.S. airports both following the president’s announcement and in the weeks leading up to it appear to have been responsible for outsized coronavirus outbreaks in many states, and especially in New York. One investigation of U.S. coronavirus data found that travel from Europe was responsible for the initial spread of COVID-19 in at least 13 states, while Chinese travel infected only six. Particularly dangerous were the weeks immediately before Trump’s announcement, during which many Americans working and traveling in Europe, having witnessed the China ban and anticipating a similar one for Europe, decided to return home. During that period, more than 10,000 direct flights from Europe arrived at 12 major U.S. airports, carrying an estimated one million passengers, none of whom received quarantine orders or contact-tracing interviews. And in the four weeks after the Europe ban went into effect, there were at least 246 flights to U.S cities from western European countries.

The outsized COVID-19 epidemic in New York City appears to be directly traceable to the burst of travel surrounding the ban. Between February 5 and March 14, almost 4,000 direct flights from Europe arrived at New York’s international airports, and in the period after the ban, there were at least 246 flights. New York City’s infections, according to a study by New York University researchers who traced the virus substrains detected in patients, mostly originated in Europe; about two-thirds of the city’s cases were traced directly to Europe, and a large part of the other third came from states that also got their major infections from Europe.


The countries that have done the best job preventing foreign infections of COVID-19 have either closed their borders completely (barring all foreigners and subjecting nationals to mandatory quarantine) or left them open and carefully monitored new arrivals. New Zealand barred entry to nearly all travelers on March 19 and has seen hardly any coronavirus spread since then. Prime Minister Jacinda Ardern’s government booked up a large number of hotels near airports, filled them with medical and catering staff, and turned them into “assisted self-isolation” facilities where returning New Zealanders were required to stay for two weeks. (Early on, some travelers were allowed to isolate at home, under police watch, if they could prove they had the space and resources to do so.) Taiwan enforced a similarly strict quarantine mandate, requiring all arrivals to have their precise location tracked for two weeks using smartphone apps. Police paid visits to those whose apps showed movement away from their homes. Such measures may have been easier in small, island countries: New Zealand has had only 40,000 citizens arrive during its lockdown, and Taiwan had quarantine-monitoring technology and staff already in place from previous pandemics. But both nations have so far succeeded in keeping the virus in check: New Zealand has seen only 21 COVID-19 deaths to date, and Taiwan has seen only seven.

Other places have succeeded with the opposite approach, leaving borders at least somewhat open and allowing citizens to return gradually while carefully monitoring the spread of the disease. Hong Kong allows travelers to fly into the city but requires them to take a COVID-19 test on arrival and then wait at desks in a gymnasium-sized isolation hall for eight hours until the results are ready. The crowded city has had only four coronavirus deaths.

Germany has also managed to slow the virus’s spread. After a big initial outbreak in February, when many young people returned from ski trips in Italy, the German government asked citizens to restrict travel. It set up checkpoints at some international borders, but it did not issue sudden orders for Germans to come home. The country’s normally busy borders with Belgium and the Netherlands remained open and unguarded, and airlines and trains continued to operate. Germany saw a rapid decline in new infections until very recently, when the country began reopening schools, businesses, and restaurants. Norway has had relative success with a similar strategy, shutting its ports and airports on March 16 but keeping its heavily trafficked border with Sweden open, relying on rigorous testing and contact tracing to control the disease’s spread. By not suddenly announcing travel bans or border closures, these countries avoided a rush that would have overwhelmed public health staff and resources. As a result, they were able to monitor the trickle of people crossing the border and quarantine them if necessary.

From the moment it left China in early January, the novel coronavirus has proven to be a truly global traveler, stubbornly unconcerned with tough laws or bold proclamations intended to stop human movement. No country of any size has managed to prevent the coronavirus from entering its territory. What the last five months have shown is something that migration experts and epidemiologists have known for decades: that suddenly slamming borders shut during a pandemic is counterproductive unless large-scale resources and thousands of staff are deployed to isolate and monitor the inevitable cascade of returning nationals.

Even the countries that closed their borders entirely and implemented strict quarantine measures for returning nationals did not assume that border closures alone would protect them. They did what the Trump administration has so far steadfastly refused to do: test, trace, and isolate until the virus was mostly stamped out. Although it is important to stop people from moving around as much as possible during a pandemic, one hard lesson of the coronavirus crisis is that closing borders quickly often does the opposite.