Restricting Air Travel Cannot Stop Flu Pandemic

Researchers at the Center for Infections, Health Protection Agency (HPA, London, UK), developed a metapopulation model that consists of a set of coupled dynamic epidemic transmission models, using information already available about how flu viruses spread, particularly information recorded during the worldwide flu outbreak in 1968-1969. Coupling between cities was estimated by using data for 2002 received from the International Air Transport Association (IATA, Montreal, Canada) on flights between 105 cities, including the 100 with the highest number of international scheduled passengers and all 52 flights used in the 1968-1969 outbreak. With the mathematical model devised, virtual experiments were carried out by simulating worldwide outbreaks on a computer. The researchers looked at how the virus might spread from one city to another and how travel restrictions might reduce the rate of spread. Allowances were made for seasonal travel, number of air passengers, and the fact that some people are more resistant to infection than others.

The researchers concluded that restrictions on air travel would achieve very little. This is probably because, compared with some other viruses, the flu virus is transmitted from one person to another very quickly and affects many people. Once a major outbreak is under way, banning flights from affected cities would be effective at significantly delaying worldwide spread only if almost all travel between cities could be stopped almost as soon as an outbreak was detected in each city. The results were published in the June 2006 issue of PLoS Medicine.

"The results here suggest that resources might be better directed at reducing transmission locally and at attempting to control outbreaks during the earliest stages of sustained human-to-human spread, when movement restrictions are likely to be a more valuable containment measure, " wrote Dr. Ben S. Cooper and colleagues of the statistics, modeling, and bioinformatics department at the HPA.



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