Why not close the borders?

I’ve done a lot of swine flu reporting this week, and one question that keeps coming up is why DHS doesn’t just close the Mexican border. Congress has held a few swine flu hearings; someone invariably asks this same question at each hearing.

Let me take a stab at answering it, based on conversations I’ve had this week with scientists and doctors and other people much smarter than I am.

First, a little history. The chart on the right (courtesy of Wikipedia) shows the spread of the Black Plague through Europe in the 14th century. You can see the disease started along the Mediterranean coast and then moved across the continent in bands. It’s a fairly straightforward progression, moving slowly across Eastern Europe and into Russia.

This is how pandemics used to spread. They were limited because people didn’t travel much; when they did, they traveled short distances, and only as fast as their horse could move. So in those days there might have been some benefit to closing borders.

But diseases don’t travel in slow bands anymore. Let’s say we somehow closed the entire Mexican border — unlikely, by the way, since it is the second-busiest border crossing on the planet. An infected person could still get on a plane in Mexico City and fly to England and spread the disease to a dozen new people — all within 24 hours or so. (This has happened, in fact: people in at least a dozen countries have swine flu.)

And then a newly-infected Briton could get on a plane at Heathrow and fly to New York, bringing the disease to the U.S.

That’s why public health officials don’t recommend closing borders. It wouldn’t stop the spread of the disease — not in our interconnected world, anyway — but it would do a lot of damage to the U.S. and Mexican economies, which depend on a huge volume of cross-border traffic.