The evidence on travel bans for diseases like coronavirus is clear: They don’t work

Editor’s note, April 22, 2021: This article, published in January 2020, does not reflect the emerging science around travel restrictions to prevent the spread of epidemics. For more on coronavirus travel restrictions, see our latest coverage.

On Sunday evening, the US government followed a slew of other countries and began enforcing a new coronavirus travel ban: Foreigners who visited China in the past two weeks are temporarily barred from entering the country, while US citizens who have been to China’s Hubei province — where the outbreak originated — will have to be quarantined for 14 days.

Russia, Australia, Japan, and Italy have announced similar restrictions.

These types of travel restrictions to control the spread of disease have been tried since 1377, when the Mediterranean city of Dubrovnik — formerly known as Ragusa and now part of Croatia — imposed a 40-day isolation period on ships suspected of carrying the black plague that were entering the city.

Since then, nearly every new pandemic threat has come with efforts to seal up borders. During the 2003 SARS outbreak, affected cities around the world from Toronto to Beijing experimented with shutting down travel and screening people at borders for the disease. The 2014-2016 Ebola epidemic was met with calls by US politicians, including then-New Jersey Gov. Chris Christie and Donald Trump, to close off travel with West Africa.

With more than 17,000 cases of the new virus in China, travel restrictions are surfacing once again. “We are preparing as if this is the next pandemic,” Nancy Messonnier, director of the National Center for Immunization and Respiratory Diseases, said on Monday. “Strong measures now may blunt the impact of this virus on the US.”

But it would be one thing if there were strong evidence that travel bans work to stop the spread of the disease. Instead, “Travel restrictions can cause more harm than good by hindering info-sharing, medical supply chains and harming economies,” said the World Health Organization director general, Tedros Adhanom Ghebreyesus.

“These types of measures have been shown to be ineffective at halting the spread of the viruses,” said Adam Kamradt-Scott, a professor in global health at the University of Sydney who studies global health security.

At best, travel restrictions, and even airport screenings, delay pathogens from moving — but they don’t impact the number of people who eventually get sick. Rather, they make it harder for international aid and experts to reach communities affected by disease. They are also expensive, resource-intensive, and potentially harmful to the economies of cities and countries involved. A look at the research helps explain why.

After HIV/AIDS was discovered in 1984, governments around the world imposed entry, stay, and residence restrictions on people with the disease. As one 2008 study notes: “Sixty-six of the 186 countries in the world for which data are available currently have some form of restriction in place.” In the US, the ban — instituted by President Ronald Reagan in 1987 — was only lifted when Obama came into office.

HIV/AIDS managed to spread anyway, reaching pandemic proportions by the 1990s. This 1989 review of HIV/AIDS travel restrictions found they were “ineffective, impractical, costly, harmful, and may be discriminatory.” Prevention of HIV worked better than travel restriction, the authors concluded. “The rapidity and extent of HIV spread in any country is primarily determined not by HIV-infected travelers but by the risk-producing activities of its citizens, regardless of whether HIV is introduced by foreign travelers or returning nationals.”

Temporary flight bans and decreases in air travel following 9/11 provided a natural experiment in the impact of travel on seasonal influenza. Researchers found the reduced movement of people didn’t stop the spread of the flu; it delayed it by a couple of weeks and led to a prolonged flu season.

The researchers didn’t test whether this delay reduced flu cases or saved lives. But a look at the data from the Centers for Disease Control and Prevention shows that flu deaths actually spiked during the 2001-2002 flu season, rising from about 3,900 the year before to more than 13,000 post-9/11. This isn’t to say that 9/11 had anything to do with the increase in flu deaths, but rather that travel bans didn’t seem to prevent them.

One 2006 study modeled various approaches for stopping the spread of H5N1 avian flu. It found that restricting travel wasn’t effective: “Our simulations demonstrate that, in a highly mobile population, restricting travel after an outbreak is detected is likely to delay slightly the time course of the outbreak without impacting the eventual number ill.”

It’s expensive and nearly impossible to seal off the borders of a country, the authors of the paper wrote. People will inevitably move — even indirectly from the countries that are quarantined.

Kamradt-Scott shared a revealing example: During the height of the SARS outbreak in 2003, he had a colleague who wanted to return to the UK from Toronto, one of the cities most affected by the virus. So she caught a domestic flight from Toronto to Vancouver, then boarded a flight to London. “When she arrived at Heathrow [airport] and authorities asked her, ‘Have you been to Toronto,’ she said no and walked right through.”

After the arrival of H1N1 swine flu in 2009, some countries imposed travel restrictions on flights going to and coming from Mexico, resulting in a 40 percent decrease in overall travel volume. A study looking at this event found it “only led to an average delay in the arrival of the infection in other countries (i.e. the first imported case) of less than three days.”

Again, reduced travel delayed (by three days!) but didn’t stop the disease spread. The authors wrote, “No containment was achieved by such restrictions and the virus was able to reach pandemic proportions in a short time.”

As the US government expands its effort to screen people at airports for the new coronavirus, it’s worth looking at what happened in Canada during the SARS outbreak of 2003. Canada was one of the countries most affected: The virus caused hundreds of cases and 44 deaths, and wreaked havoc on the nation’s airports, health care system, and economy. A major effort to stop the spread of the disease involved screening millions of people at airports, through the use of thermal scanners and sending passengers who might have symptoms to nurses or quarantine officers for an assessment.

According to a Canadian government report on the effort, some 25,000 residents in the greater Toronto area were quarantined and millions more were screened at airports. The effort was a waste of money and human resources; it didn’t pick up a single case of the disease. From the analysis:

Roughly 9,100 passengers were referred for further assessment by screening nurses or quarantine officers. None had SARS. The pilot thermal scanner project screened about 2.4 million passengers. Only 832 required further assessment, and again none were found to have SARS. In other countries, the yields for airport screening measures were similarly low.

So not only does the evidence suggest that travel restrictions don’t work, it doesn’t account for the devastating economic impact and potential harm to the outbreak response that such restrictions can bring about.

In the case of China, which currently has some 50 million citizens under quarantine, there’s also the question of whether these measures are too little, too late. “We are already hearing reports of the coronavirus in distant regions of the country, and there are increasing numbers of exported cases internationally,” Isaac Bogoch, a global health and infectious disease researcher at Toronto General Hospital Research Institute, told Vox.

Are there alternatives? Instead of using airport screening and entertaining plans to seal borders, the governments of the world should focus their attention and resources on educating travelers about this new disease, and on helping China respond to the outbreak. We know this for sure: The longer this virus spreads there, the more people get the disease, and the greater chance it has of spreading throughout Asia and the world.