Swine Flu May Not Be Any Deadlier This Fall: Experts

The theory that a relatively mild outbreak of a new flu virus in the spring predicts a more severe, deadly outbreak in the fall isn't borne out by a look back at prior epidemics, two U.S. experts say.

"Pandemic history suggests that changes neither in transmissibility nor in pathogenicity are inevitable," concluded Drs. David Morens and Jeffery Taubenberger, infectious disease experts at the U.S. National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health.

In an article published in the Aug. 12 issue of the Journal of the American Medical Association, the experts take on a much-publicized theory that's helped stoke fears about a resurgence of swine flu in the Northern Hemisphere this fall.

The so-called "herald wave" theory stems from the belief that the deadly 1918-19 flu pandemic began with a milder spring wave of illness, which got more deadly as the virus spread throughout the summer, picking up lethal mutations. The 1918-19 "Spanish Flu" is estimated to have killed between 20 million and 40 million people worldwide.

However, while flu outbreaks were noted in Europe in the spring of 1918, no viruses from these outbreaks "have yet been identified," Morens and Taubenberger noted. And the actual course of the 1918 pandemic flu varied greatly around the world -- most areas experienced no "spring wave" at all, and the timing of successive waves changed between regions and even between countries, the researchers said.

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