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April 28, 2006

Unstoppable

The Globe and Mail reports on a new computer model of an H5N1 pandemic: No stopping bird flu, studies conclude.

The story describes a study led by Dr. Neil Ferguson that estimates one-third of Americans would be infected by avian flu—but if enough antivirals were available, the infection rate could drop to 28 percent.

The US population is expected to reach 300,000,000 in October 2006. So the Ferguson model predicts 100 million infected if nothing is done, and 84 million if enough antivirals miraculously appear from nowhere. Sixteen million spared the infection would be a goal worth achieving, but from what we're told it's not likely.

So here's a little speculation, based on a crude analogy with 1918-19: A three-wave pandemic, spring-fall-spring. Twenty-five million Americans sick in the first wave, fifty million in the second, and twenty-five million more in the last waves. Assume a comparable 33 percent infection rate around the world: two billion cases, in the same proportions as in the US.

In the fall wave, one in six Americans is sick. A billion other people are sick at the same time. The global infrastructure is held together by a coalition of saints, heroes, and lunatics, many of whom fall ill and die on the job.

Assume that the case fatality rate around the world is 2.5 percent, about the toll the US suffered in 1918-19 (other countries seem to have suffered much higher rates). So the US loses 625,000 people in the first spring wave, tries to recover over the summer, and then loses 1,250,000 between Labor Day and Thanksgiving.

In the final wave, another 625,000 Americans die. Meanwhile 50 million more die worldwide in the three waves. Collateral damage is on top of that: deaths due to untreated medical conditions and injuries, malnutrition, and so on.

Please don't take these numbers as firm predictions. This is a very crude extrapolation, the kind of thing we SF writers like to fool around with (and we couldn't even predict the personal computer, so what do we know?). And as awful as it sounds, it's no worse, proportionally, than the Spanish flu. Two-thirds of us won't catch even a mild form of H5N1.

To infect just a third of us, H5N1 may have to give up so much virulence that only a fraction of 1 percent actually die. Or it may keep its 55 percent mortality and kill so many people, so fast, that it smothers itself by running out of victims. The worst-case scenario, of course, is that it stays lethal while spreading easily and swiftly around the world.

But we still have no idea which scenario, if any, will come true.

Posted by dymaxion at April 28, 2006 03:03 PM

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