Why Border Controls Can't Keep Out the Flu Virus

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Jorge Duenes / Reuters

A man wears a mask to protect against swine flu as he crosses to Tijuana through a turnstile

The World Health Organization (WHO) raised the pandemic alert level on Wednesday evening to phase 5, signaling that the first influenza pandemic in more than 40 years was imminent. That announcement came on a day when the H1N1 swine flu virus continued to spread worldwide, with new cases confirmed in Austria, Germany, Britain, New Zealand and Israel, bringing the global caseload to 148.

The hardest hit countries are still Mexico and the U.S., where the virus is spreading easily from person to person — the main reason behind the WHO's decision to raise the pandemic alert from phase 4 to 5. In the U.S. there are now more than 90 confirmed cases in 10 states, with the first fatality reported on Wednesday morning — a 22-month-old Mexican boy who died in Texas. In Mexico more than 150 people have died of what is suspected to be swine flu, with more than 2,400 suspected infections — though only seven deaths and 26 cases have been confirmed as swine flu in a lab. (See pictures of thermal scanners hunting for swine flu.)

But the pandemic threat goes well beyond one or two countries. "An influenza pandemic should be taken seriously because of its capacity to spread rapidly," said WHO director-general Margaret Chan. "We do not have all the answers now. But we will get them."

With the H1N1 swine flu virus seemingly entrenched in both Mexico and the U.S., and continually surfacing elsewhere, a pandemic may be inevitable — flu viruses are extremely transmissible and hard to control. But that hasn't stopped health officials from trying. In the U.S. President Barack Obama said on Wednesday that affected schools "should strongly consider temporarily closing so that we can be as safe as possible," prompting the closure of schools with confirmed cases — involving some 50,000 students — in several states. At his news conference on Wednesday night, Obama also said that "every American should know that their entire government is taking the utmost precautions and preparations." (See five things you need to know about swine flu.)

Those measures include strengthening surveillance of travelers entering the U.S., examining and testing people who might be exhibiting flu-like symptoms and alerting U.S. citizens in Mexico, where the disease still seems to be at its worst. Meanwhile, other countries have placed far stronger restrictions on travel to Mexico, in an effort to cut off the spread of the disease. Cuba and Argentina have temporarily banned flights to and from Mexico, Japan has stopped giving visas to Mexicans who arrive in the country, and France is putting forward a request to suspend all flights between the European Union and Mexico.

In hearings on Wednesday, members of Congress sharply questioned Secretary of Homeland Security Janet Napolitano on the possibility of virtually sealing off the border with Mexico. Said Republican Senator John McCain in a statement, "I continue to believe that all available options to end this crisis must remain under consideration, including closing the border if it would prevent further transmission of this deadly virus."

But Napolitano said the U.S. has no plans to close the border with Mexico, a stance that the Centers for Disease Control and Prevention (CDC) and WHO support and which Obama reiterated at his press conference. "Intensive efforts at the border are not effective means for protecting against an infectious disease," said acting CDC director Richard Besser. Still, if the swine flu continues to worsen in Mexico, it's not hard to see how Obama and other world leaders would come under increasing pressure to try to wall off Mexico — just as an infected patient might be quarantined to prevent the spread of the disease. (Read: "Battling Swine Flu: The Lessons from SARS.")

Health officials argue that because the H1N1 swine flu virus is already present in so many countries, and readily capable of spreading from person to person, it's far too late to try to isolate one or two countries. Although uninfected countries may be able to delay the introduction of swine flu by imposing draconian limits on international travel, they would not likely be able to stave off the virus for good — and the economic losses resulting from the travel ban may far outweigh any benefits. One 2007 study by the Brookings Institution estimated, for example, that a 95% reduction in U.S. air travel would cost the economy $100 billion a year.

"Once the virus has spread beyond its initial focus, travel restrictions just aren't effective," says Ira Longini, a biostatistician at the University of Washington. With 4,000 flights a day between the U.S. and Mexico, "it's not worth the social disruption it would cause."

That's not to say that very strict restrictions wouldn't have some effect on slowing the virus. In a 2006 study, Harvard epidemiologists John Brownstein and Kenneth Mandl examined the effect of the sharp reduction in air travel after the Sept. 11 attacks on that year's flu season. They found that the initial flight ban and general decline in air travel in the weeks after delayed the onset of the flu season but did little to reduce the overall number of infections and deaths that year.

The data matches computer models run by biostatisticians like Longini, who found that even the strictest limits on air travel would only slow the start of a flu pandemic, not stop its spread. But, again, while that strategy may benefit countries that have not yet been infected with swine flu, there's still no way to know when it would be safe to lift those restrictions. "There's no question that air travel spreads the flu," says Mandl, a physician and researcher at the informatics program at Children's Hospital Boston and an associate professor at Harvard Medical School. "But the impact of limiting flights at this point is difficult compared to the downside of the economic impact."

As far as the U.S.-Mexico border is concerned, attempting to actually close it would be futile, since countless illegal migrants cross over to the U.S. daily. Trying to stop movement may just push travelers, and the spread of the swine flu, underground. It would create a diplomatic headache as well — the Mexican government has already expressed its concern over travel restrictions. (See pictures of the swine flu outbreak in Mexico.)

What works better are social-distancing actions on a local level — closing schools, having employees work at home and limiting public gatherings, where the flu can spread easily. Such methods worked during the deadly 1918 Spanish flu — cities that acted quickly to close schools and theaters early in the pandemic had peak death rates 50% lower than cities that acted more slowly. Today doctors could also prophylactically administer antiviral drugs to the close contacts of any swine flu patients, a strategy that has been shown to help prevent the spread of the flu. "Until you start to see really massive clusters, that can be a really effective method," says Longini.

Ultimately, however, in a world as truly interconnected as ours, we can no more cloister a single country than we could cut off a limb. The world has become increasingly one — as the rapid spread of the swine flu virus from country to country shows. "It is really all of humanity that is under threat during a pandemic," says the WHO's Chan. Whatever happens next with the swine flu — whether it burns out or sharpens — we're in this together. — With reporting by Massimo Calabresi / Washington

Read "How to Deal with Swine Flu: Heeding the Mistakes of 1976."

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