If you want to visit the Great Pyramids or the Great Wall or the Taj Mahal, forget it.

Egypt, China and India are just a few of the dozens of countries that have imposed strict travel restrictions to keep visitors, and the coronavirus, out. An analysis by NPR based on data from the found that more than three-quarters of the world's nations and territories have suspended travel from at least one other place.

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Restrictions are often promoted by politicians as a sign of strength in efforts to halt the spread of the new coronavirus. But experts say the border closures have done little to stop it. And going forward, they say, travel restrictions will play only a small role in containing the virus.

"I think they're mostly useless, to tell you the truth," says Ira Longini, a professor of biostatistics at the University of Florida who has studied the effects of restrictions. Far more important, Longini says, are domestic systems for testing and contact tracing. "You have to have the internal control strategy — that's effective," he says.

Travel restrictions have been with humanity for a long time. As early as the 14thcentury, European kingdoms would quarantine ships to try and prevent the spread of plague, according to Benjamin Mason Meier, a professor of global health policy at the University of North Carolina at Chapel Hill. The quarantines didn't always work, he says. "At the same time, it was limiting the flow of traffic that was so crucial to the livelihoods of people around the world."

In the 1800s, nations started trying to develop standardized rules around travel and disease. A series of international sanitary conventions followed in the 20th century that became the basis of the International Health Regulations, a set of rules laid down by the World Health Organization and agreed to by nations.

"The purpose is to prevent disease but to do so in a way that provides the least restriction on international traffic and commerce," Meier says.

The latest revision of the regulations was published in 2005, a few years after the first SARS outbreak. The rules state that "measures shall not be more restrictive of international traffic and not more invasive or intrusive to persons than reasonably available alternatives that would achieve the appropriate level of health protection." Nations are supposed to provide WHO with a rationale for any ban.

But all that seems to have gone out the window with this pandemic.

"I think it is kind of an intuitive human reaction to sort of pull up the drawbridge," says Tara O'Toole, an executive at the investment firm In-Q-Tel and a former top scientific official at the Department of Homeland Security. O'Toole says most research on the current pandemic shows that at best travel restrictions brought just a few days of extra time to prepare. That's because sick travelers always travel faster than governments can impose bans.

"Particularly in modern times, when we travel from one end of the globe to the other in 24 hours, the horse is already out of the barn," O'Toole says. Nevertheless, she says, she thinks initially the restrictions probably made sense, given the scale of the coronavirus crisis. Nations needed every advantage they could get.

WHO initially advised against travel and trade restrictions, but it has since softened its stance, at least somewhat. "WHO will update recommendations on appropriate travel measures and analyze their effects on international transmission of COVID-19," a statement supplied to NPR reads in part.

Even though the coronavirus has spread basically everywhere, it may make sense for some nations to keep their restrictions in place, according to Marc Lipsitch, an epidemiologist at Harvard University. That's because right now, the only way to suppress the coronavirus is through finding the sick and tracking down their contacts before they can sicken others.

"The last thing you want is a bunch of cases coming in that you can't anticipate because they're not linked to any local contacts," Lipsitch says.

He says he thinks travel restrictions may be helpful, particularly for countries that are small and can easily control their borders such as islands.

"It might be better to harm the tourism industry than to go back into a long period of generalized economic disruption from social distancing," he says.

But the United States, which is currently restricting travel from Europe, China and Iran, is a different case. At the moment, the U.S. is a major hot spot for coronavirus infections and has little to lose by letting others in. But even in the long term, restrictions don't make much sense, says Nathan Grubaugh, an epidemiologist at Yale University.

"For the U.S. to say that we can eliminate all virus in the country and then shut down all the borders so that no virus comes in would be completely off base," Grubaugh says. Domestic travelers from local hot spots will require other regions to keep watch for new infections for a long time to come. "There's so many pockets where virus can be found."

However, Grubaugh says there is another problem with reopening air travel: "The airports and flights themselves are a big risk factor," he says. Long international flights, with lots of passengers crammed together, are ideal places for the virus to spread, he warns.

How long travel restrictions will stay in place remains far from clear. Grubaugh says he thinks economic pressures will soon cause them to be lifted. But Meier says he worries that in the current era of nationalism and xenophobia, the restrictions could stick around. "They divide the world at the moment that global solidarity is most crucial to facing this common threat," he says.

O'Toole says she believes in the end, it may be testing that reopens the world to travel. "Hopefully we will get to the point where we can test people before they get on planes," she says. "So that you have a good amount of assurance that none of your fellow passengers are transmitting virus."

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