Flu WHO can't stop pandemic, modelling suggests

Discussion in 'Survival Medicine' started by Bear, Feb 21, 2006.

  1. Bear

    Bear Monkey+++ Founding Member Iron Monkey

    WHO can't stop pandemic, modelling suggests
    Feb. 20, 2006. 08:50 PM

    The World Health Organization’s plan to try to extinguish an emerging flu pandemic at its source will likely only buy the world additional time to prepare, not snuff out the threat, new mathematical modelling suggests.
    The WHO, which is devoting considerable time to developing a rapid response and containment plan, acknowledged Monday the claim is probably valid.

    But the organization would have no choice but to try if the H5N1 avian flu strain or another novel flu virus seems poised to trigger a wave of global disease and death, a spokesperson said.

    “Since we’ve been talking about this containment strategy, we’ve given the very big qualifier that we think it may fail,” Maria Cheng said from the agency’s Geneva headquarters.

    “But it’s still worth it because if it buys us some extra time, it gives countries some extra time to prepare and it gives vaccine companies more time to produce vaccine.

    “It’s something that we have to try as a global public health agency.”

    The modelling work, done by a group of researchers from Harvard University’s School of Public Health and the University of Washington, was published Tuesday in the journal Public Library of Science Medicine.

    It follows modelling studies by two groups of American and British researchers published in the journals Science and Nature last summer.

    Both estimated that with early detection of human-to-human spread of a new flu virus and rapid intervention with antiviral drugs and movement restrictions, a pandemic could in theory be stopped.

    Prior to publication of the work the WHO had expressed reservations about how workable a fire-blanket strategy, as it’s sometimes called, would be.

    The work, when published, was met with muted enthusiasm by infectious disease experts who argued that too many variables would have to go right for the goal to be achieved.

    Still, within days WHO director general Dr. Lee Jong-wook said publicly that the agency would try to put in action what the models suggested might be attainable.

    Harvard epidemiologist Marc Lipsitch, the senior author of the new modelling work, argued last summer that a key flaw in the old model was the assumption that a new emerging pandemic strain would be a one-time event, like a small fire ignited by a lightning strike.

    He and his coauthors describe a scenario that is more like a series of sparks flying off a bonfire, setting multiple small fires over a period of time.

    The fire-blanket might extinguish one or two of those blazes, Lipsitch and his colleagues agree. But with the original bonfire continuing to send off sparks, chances will rise that one will go unchecked and ignite a conflagration.

    “The earlier work focused on the potential as they saw it and the difficulties of doing it once. And we’re making the suggestion that doing it once might well not be enough,” Lipsitch said from Boston.

    Mathematical modellers have to make a series of assumptions in order to construct their models, especially with something as poorly understood as how a pandemic flu strain emerges.

    Both sides in the debate have points they use to argue that their baseline assumptions are the appropriate ones — but at present there’s no way to know which is likely to be more accurate.

    Neil Ferguson, the British modeller whose work was published in Nature, argues that pandemics are sufficiently rare events throughout history that if a single transmissible strain of H5N1 emerges and is caught, the threat will be dealt with.

    Lipsitch and his colleagues point to evidence — published by scientists from the U.S. Centers for Disease Control — that there were multiple reassorted or mutated viruses circulating before the start of the last pandemic, the 1968 Hong Kong flu.

    “(It) is consistent with the possibility of multiple introductions, but does not demonstrate this conclusively,” they admit in their paper.

    Even though they are skeptical a pandemic could be stopped, the group is not arguing the WHO should abandon the effort.

    “I strongly advocate putting eggs into that basket,” said co-author Carl Bergstrom, an evolutionary biologist from the University of Washington, adding even a failed effort could buy the world months or a perhaps a year of additional time to prepare.

    But the basket isn’t sturdy enough to hold too many eggs, the authors caution.

    “Putting a lot of hopes on it is a bad idea,” Lipsitch said.
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