When Mexico reported an outbreak of swine flu last April, fear of an epidemic quickly spread. One member of Congress claimed he knew exactly how to handle the situation. "We need to close our borders to Mexico immediately and completely until this is resolved," said Rep. Eric Massa, D-NY, a Naval Academy graduate and Gulf War veteran.

Nobody listened to him.

Now the science is in. And guess what? It makes the Congressman and all the other seal-the-border alarmists look foolish.

Dr. Kamran Khan at St. Michael's Hospital in Toronto leads a research team that studies international air travel to help predict the spread of infectious diseases, like the swine flu (officially called H1N1).

Last week, the New England Journal of Medicine published the results of their work. It showed that the swine flu had spread across the globe in a way that perfectly matched air travel patterns.

The researchers found that, from March to April, two million people flew out of Mexico. They traveled to 1,000 cities in 164 countries. And where they went, the flu went.

Closing the land border with Mexico, even if that were possible, would have done nothing to stop the disease from spreading. Indeed, it had already gone global before Mexican officials recognized they had a serious problem. (Infected individuals "shed" virus cells before they know they are sick or show signs of a sniffle.)

Four of every five air travelers leaving Mexico landed in the United States. The disease was through baggage claim and out the door before Massa's press release was even drafted.

Well, some might ask, why not just quarantine the whole country? Even if Mexican officials knew about the flu on the first day of the outbreak--a medical impossibility--this gambit couldn't work.

The idea of sealing off an entire country is wildly impractical. In this case, it would have meant barring a million or more people--tourists and natives alike--from leaving. Think of it as a million-man GITMO.

Global quarantine makes even less sense when considering what the disease actually did. Yes, millions in Mexico got sick. And U.S. health officials estimate just over one million Americans have come down with it, so far. Cases have been reported as far away as Nepal. Yet, across the globe, the World Health Organization has confirmed a grand total of 311 deaths so far.

Closing the border would not have stopped the disease, but it would have created more suffering than the disease itself. That's what happened in 2003, when China implemented a "panic" response to the outbreak of Severe Acute Respiratory Syndrome (SARS). By some estimates, China's overreaction cost the mainland economy 1 percent of its gross domestic product, some $50 billion. It cost Hong Kong 2.5 percent of its GDP.

Mexico is America's third largest trading partner. Last year, trade between the two nations totaled $367 billion. Stopping that trade would be like firing a shotgun blast into the heart of Mexico's economy and the foot of our own.

Scientific studies can warn us away from "stupid" measures for dealing with emergencies. They can also point us toward effective responses.

For example, Herman Leonard and Arnold Howitt of Harvard University analyzed how societies should organize in the face of large-scale disasters, like a killer pandemic. They concluded that preparedness measures are some of the most effective means to improve disaster response.

There are limits, of course. The necessary vaccine can't be produced until the disease exists. However, much can be done "up front" to prepare for pandemics.

The most important element, according to the researchers, is to have a strong, vibrant, and robust health care system. Right now Congress is debating healthcare legislation. If the Obama administration gets its way, our current system will be fundamentally changed in ways that will drive healthcare costs through the roof and strangle the economy.

James Jay Carafano is Senior Research Fellow in national security policy at The Heritage Foundation.