Scientists study past flu pandemics for clues to future course of 2009 H1N1 virus

A commonly held belief that severe influenza pandemics are preceded by a milder wave of illness arose because some accounts of the devastating flu pandemic of 1918-19 suggested that it may have followed such a pattern. But two scientists from the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health, say the existing data are insufficient to conclude decisively that the 1918-19 pandemic was presaged by a mild, so-called spring wave, or that the responsible virus had increased in lethality between the beginning and end of 1918.
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