Study shows 'direct link' between air travel, flu spread

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Scientists have found what they call the first real evidence that restricting air travel can delay the spread of flu -- a finding that could influence government plans for battling the next influenza pandemic.

Air travel has long been suspected of playing a role in flu's gradual spread around the globe each year, but yesterday, Boston researchers said they finally have documented it: The drop in air travel after the September 11, 2001, terrorist attacks seemed to delay that winter's flu season by about two weeks.

"This is the first time that a study has been able to show a direct link between the numbers of people traveling and the rate of spread of a virus," said John Brownstein, an epidemiologist at Children's Hospital of Boston, who led the research.

Other scientists stress that the study doesn't prove that restricting air travel helps in the long run -- there was no drop in the number of deaths, just a delay. So if a pandemic were to strike, the question is whether a mere two-week delay would outweigh the economic chaos of severe travel restrictions.

"You wouldn't want to have people look at this and say, 'Ah, this is overwhelming evidence that if the pandemic occurs, we should shut down air travel,'" said Dr. Anthony Fauci of the National Institutes of Health, the government's chief influenza specialist.

"What does it buy you? That's the real critical issue."

Added Dr. William Schaffner of Vanderbilt University, who advises the government on flu issues: "We're all sure that airlines play a role. ... Leaping from this sort of analysis to interdiction of air travel I think is provocative, and we have to be very careful about that."

It's not that a lot of people catch the flu from sneezy fellow passengers, although that's possible. Instead, Mr. Brownstein says, travelers who may start a trip before flu's symptoms kick in infect the people they're visiting -- or they catch the virus in one city and carry it back home.

People easily spread the flu through coughs, sneezes and germs on their hands. But scientists don't understand how a community outbreak ripples outward until each winter's flu strain spreads across countries. Plus, every few decades, a new and virulent flu strain causes a worldwide epidemic. Better understanding of those geographic patterns might help stem the next such pandemic.

Previous studies suggest that young children who bring the flu home to older relatives spark community outbreaks, which spread among U.S. cities and states when the sick go to work instead of recuperating at home.

The study appeared yesterday in the online science journal PLoS Medicine.