An audacious global plan to stop future influenza pandemics in their tracks-- adopted by the World Health Organization (WHO) last month--may have an important flaw, researchers say in a new paper. The plan, based on containing an epidemic where it first erupts, may initially work, they write, but later-emerging pandemics would likely overwhelm it.
Mathematical models published in August in Nature and Science (ScienceNOW, 3 August 2005) predict that by dispensing huge quantities of antiviral drugs to the area where human-to-human transmission of a new influenza virus begins--the prelude to a pandemic--and enacting rigorous quarantine measures, it might be possible to nip a pandemic in the bud. On 27 January, WHO published the first draft of such a "rapid response and containment" protocol, which the agency says is worth a try.
The scheme may halt the first pandemic, write Marc Lipsitch and colleagues at Harvard and Carl Bergstrom at the University of Washington (UW) in Seattle, in a paper published online today in Public Library of Science Medicine. The problem, as the authors see it, is that just as a parched forest rarely sees just one brushfire, if one pandemic virus emerges, it's likely that another will pop up somewhere else soon. And the more this happens, the more likely one of the containment efforts will fail, especially because, like fire brigades, the world would run out of manpower and resources.
Not that containment at the source shouldn't be tried, Bergstrom hastens to add. Even if it succeeds just once or twice, it "would buy time, which is incredibly useful," he says, because scientists and policymakers would better understand their future foe. But in the end, the team's models show, the containment strategy may buy just a few years.
"I don't agree with that argument at all," counters UW modeler Ira Longini, the lead author of last year's Science paper. He believes the emergence of a pandemic virus in a human host--through mutations or recombination with a human flu virus--is and will remain a very rare event. The arrival of one pandemic virus doesn't mean the next one is around the corner, he says.
WHO influenza expert Michael Perdue agrees and says the new paper won't cause WHO to reconsider its strategy. If pandemic viruses emerged that easily, he says, the world would have seen pandemics more often, or past pandemics would have started simultaneously at several locales. But Jeremy Berg, director of the U.S. National Institute of General Medical Sciences, which funded all three studies, says that "the policymakers need to weigh the arguments in this paper, too." If the controversy illustrates anything, Berg says, it's that we still know very little about how pandemics start.