At the height of Ebola panic in 2014, some state governments used a draconian measure to keep the virus from spreading within their borders: mandatory quarantines for people returning from West Africa, where Ebola was circulating.

The federal government said the measure wasn't necessary, and the health community unanimously agreed. Locking up travelers at random for 21 days — Ebola's incubation period — wouldn't actually stop the virus from moving. Still, some governors went ahead with the quarantines anyway.

Perhaps the most vocal advocate was New Jersey Gov. Chris Christie. He famously defended his decision to detain a nurse named Kaci Hickox in a tent outside the airport on her arrival from fighting Ebola in West Africa —and attracted criticism from health officials everywhere.

Now history is repeating itself. This time, the viral threat is Zika, which has been circulating in South and Central America. And Christie, now a Republican presidential candidate, is reiterating the lock-'em-up approach. At a GOP debate this weekend, when moderator Martha Raddatz asked if he'd quarantine people traveling back from the upcoming Olympics in Brazil, Christie said plainly, "You bet I would."

Clearly, he feels this works politically. But science would suggest it doesn't work medically. History has shown, again and again, that travel bans and mandatory quarantines don't actually help stop viruses from moving. They're sloppy, costly, and can have negative effects on public health and the economies of the countries involved.

Travel restrictions don't stop viruses from moving

In a detailed look at the evidence on pandemic travel restrictions with Vox colleague Steven Hoffman, we found they have unanimously failed to stop viruses from reaching new places. Travel restrictions for those with swine flu achieved exactly "no containment." Airport screening after SARS didn't catch a single case. Travel restrictions to stop the spread of bird flu didn't cut infections. That's not to mention the failure of travel bans to stop HIV/AIDS from reaching pandemic proportions. This is why health officials reacted so strongly to quarantine measures like Christie's.

As we wrote, travel restrictions also render useless two of the best methods we have for stopping viruses: They can make it harder to do disease surveillance by driving travelers underground. They can also discourage researchers, health professionals, and other aid workers from going to regions where viruses are spreading to help stop outbreaks at the source.

There's also the effect of travel and trade restrictions on local economies. Because of the Ebola crisis, the World Bank Group estimated that the West African countries at the center of the outbreak — Guinea, Liberia, and Sierra Leone — lost out on about $1.6 billion in economic growth in 2015. These were cash-strapped countries that already had limited resources to fight off viruses.

Similarly, the South American countries hit by swine flu suffered economic losses ranging from 0.5 to 1.5 percent of their GDPs. This is part of the reason why, with the World Health Organization's announcement about Zika as a public health emergency, they recommended no travel or trade restrictions.

There's also some question about whether travel restrictions and quarantines violate people's civil liberties. Hickox, the nurse who was detained by Christie, filed a lawsuit against him, alleging she was isolated without cause. On Monday, students at Yale Law School launched a big class-action case against Connecticut, alleging its Ebola quarantines eroded civil liberties. The results of both cases are pending, but they raise questions about how quarantines can violate people's individual rights — and how they should be handled in current and future pandemics.

Why Zika quarantines make no sense



Ebola was a deadly virus and could potentially sicken or kill anyone who came into its path. It was also spread from person to person through direct contact with the bodily fluids of someone who was infected. Even here, though, health officials didn't think quarantines of all travelers could help stop the virus from spreading.

Zika is a much different virus. It is spread mainly through mosquitoes, and most people show no symptoms of the disease. A traveler would need to be returning to a region where the mosquito that carries the virus is present in order to pose an outbreak threat. So simply quarantining everybody makes little sense.

The reason the health community is concerned about Zika is because of its potential to cause birth complications among pregnant women. While this link isn't proven, research increasingly suggests there's a link between the virus and microcephaly, a congenital condition that stops babies' heads and brains from reaching full size.

The Centers for Disease Control and Prevention and other health bodies have addressed that threat by warning pregnant women or women who may become pregnant soon to delay trips to countries where Zika is circulating. They've also advised men who were traveling in the region to practice safe sex with their partners after returning home, as we're learning the virus may also be sexually transmitted in rare cases.

"Quarantine would be a very extreme measure given that the primary mode of transmission is through mosquito bites," said Kamran Khan, an infectious diseases doctor who founded Bio.Diaspora to track emerging viruses. "While it is true that there have been — literally — a couple of instances where Zika transmission has been suspected or documented through sexual activity, Zika transmission won't occur through casual contact with others. In that regard, quarantining travelers doesn't make sense."

Isaac Bogoch, a tropical infectious diseases specialist at the Toronto General Hospital, said there are many other evidence-based measures that would actually protect the public from the mosquito-borne disease, and the US is doing them already: warning people who are traveling to affected areas to use mosquito prevention techniques, mobilizing mosquito control efforts in areas of the US with the mosquitoes that carry the virus, and issuing travel advisories targeting those at risk of Zika complications, such as pregnant women.

These measures are reasonable and science-based, he said. Simply quarantining anybody who returns from a country where Zika is spreading is not.