Stopping a Pandemic Before It Starts

3 August 2005 (All day)

Stop right there. A computer model shows how a new pandemic might spread in Thailand. With massive prophylaxis, the outbreak might end after just a few hundred cases.

It might just work. If a pandemic influenza virus breaks out somewhere in Southeast Asia, massive amounts of an antiviral drug called oseltamivir, combined with draconian measures to limit people's movements and contacts--and some luck--may stop the virus dead in its tracks, according to two computer models. Such an effort could save millions of lives around the world, the authors say.

Both studies, one published online today by Nature, the other by Science, used Thailand as the presumptive ground zero, in part because current pandemic worries focus on H5N1, the bird flu strain haunting Southeast Asia (ScienceNOW, 16 June). Ira Longini, a modeler at Emory University in Atlanta, Georgia, and his colleagues simulated an imaginary population of 500,000 people in a rural part of the country; Michael Ferguson of Imperial College London built a model based on the 85 million people living in Thailand and a 100-kilometer-wide border zone in neighboring countries.

Both then introduced a pandemic virus and looked at whether it could be contained by giving a 10-day prophylactic course of oseltamivir to the contacts of every suspected flu patient--either by treating everyone in their household, school, or workplace, or by simply giving it to anyone living within a certain radius. In both models, the drug regimens were supplemented with additional measures such as closing schools, asking people to stay home as much as they could, or restricting travel into and out of the hot zone.

The more such measures were deployed, the higher the chances that the pandemic petered out, both studies conclude. But success depended critically on several conditions: The pandemic virus could not be too infectious, the first cases had to be found within a couple of weeks, and all contacts of patients needed to be given the drug within a day or two.

Those are some pretty big ifs, says Harvard epidemiologist Marc Lipsitch. "The models make sense, and we should seriously consider this approach," he says. "But the take-home message is there's no way we can count on this." But Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, Twin Cities, says he puts very little stock in such models, and he worries that the findings may lead other countries to become complacent about their own pandemic preparedness.

The World Health Organization (WHO), which the authors say should manage the necessary stockpile of up to 3 million oseltamivir treatment courses needed, is "interested" in the approach, says pandemic chief Margaret Chan, but more research, as well as discussions with the affected countries, are needed to find out whether it is feasible. The Thai government, for its part, wants to explore the option as well, says Supamit Chunsuttiwat, a senior expert for communicable diseases at the Ministry of Public Health. The two papers, he says, "give us some hope."

Related sites
Abstract of the Longini paper
Abstract of Ferguson paper
WHO statement about the two studies

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