You might think that shutting down air travel from cities affected by a dangerous new influenza strain would put a brake on the subsequent global march of that virus--but you'd be wrong. A new study has found that limiting air travel would have little effect on an influenza pandemic.
Most experts expect that from the moment a pandemic starts, it will take at least six months to develop and mass-produce an effective vaccine against whichever the culprit strain. That's why several recent modeling studies have compared strategies that might buy more time. In a paper published online by Nature on 26 April, for instance, mathematical biologist Neil Ferguson of Imperial College London and his colleagues looked at various strategies the United States and the United Kingdom could implement. Closing the borders and limiting domestic travel weren't very effective, they found, but isolating patients, quarantining their household contacts, and prophylactic use of an antiviral drug were.
Now, a paper published in the June issue of the online journal PLoS Medicine zooms in on the travel bans and takes a global perspective. Modeler Ben Cooper and his colleagues at the Health Protection Agency in London used data from the International Air Transport Association about air travel between 105 major cities around the world to model a hypothetical influenza pandemic that started on 1 June of a given year, in Hong Kong. They found that banning travel from flu-affected cities--which they assumed would be implemented after a city has 100 symptomatic cases--had little effect on the overall spread of the pandemic; the virus just reached cities elsewhere on the planet a couple of days later than it did without grounding planes. Only when a travel ban is implemented immediately after the first detection of the virus, and is 99.9% effective, will it significantly slow down the pandemic, the team found.
"It confirms on the global scale what we knew on a local scale," adds Ira Longini, who models infectious diseases at the University of Washington in Seattle. "Flu spreads so explosively that you would have to be incredibly draconian to stop it." The study "adds to the evidence that international travel restrictions have little role in how we should respond to a new influenza pandemic," says Ferguson.