Virus trackers at Columbia University College of Physicians & Surgeons have found that new strains of flu emerge each year from Southeast Asia before spreading throughout the world.
A map of the movements of H3N2 flu, the most common strain before “swine flu” emerged, reveals that the virus spreads through eastern Asia before leaping to the United States, which then seeds many other countries, particularly in South America.
The rich details of the map – uncovering flu’s spread from country to country – may help prevent future vaccine failures, the researchers say.
Vaccine failures occur because health officials must pick the strains to include in the annual vaccine several months before flu season begins.
“The problem is that viruses evolve so fast, sometimes the wrong strains are selected,” says Raul Rabadan, PhD, assistant professor of biomedical informatics and one of the researchers behind the analysis. “If we have a better way to predict which strains will become dominant, we can develop better vaccines.”
Knowing where to look for new viruses is key to better vaccine development. If new viruses arise locally, as one theory suggests, “that means if you want a vaccine for Germany, you should look at viruses in Germany to make your selection,” Rabadan explains. If new viruses emerge from the tropics, as another theory suggests, a German vaccine-maker should look in tropical Asia or Central America.
Previous studies have suggested Southeast Asia, and China in particular, as the most likely source of new viruses, but a shortage of virus data from this region and others could have biased the results.
“We have lots of data from New York and New Zealand, for example, but very little from Southeast Asia, so we can’t see the virus at all times during its spread,” Rabadan says. “It’s like we can only shine a few lights down on the world. What’s happening in the dark regions?”
Joseph Chan, a graduate student in Rabadan’s lab, and Antony Holmes, PhD, a postdoctoral research scientist, applied network theory – similar to the analysis that spawned the Six Degrees of Kevin Bacon game – to infer what happened in those dark regions. The reconstruction of the flu’s travels also revealed the most important hubs in the global influenza system.
Their analysis also suggests several different strategies – including vaccination at major hubs like the U.S., Japan, and Australia – could reduce the spread of flu worldwide.
For more information, see Network Analysis of Global Influenza Spread in the November 2010 issue of PLoS Computational Biology.