U.S. health officials are gearing up for the return this fall of the H1N1 swine flu virus that has sparked a global pandemic, but some government scientists say a second, potentially more severe wave of disease is not inevitable.
"Every influenza pandemic writes its own rules as it progresses," Dr. David Morens of the National Institute of Allergy and Infectious Diseases, part of the U.S. National Institutes of Health, said in a telephone interview on Tuesday.
Writing in the Journal of the American Medical Association, Morens and colleague Dr. Jeffrey Taubenberger said there is not enough evidence to conclude that the relatively mild spring wave of H1N1 flu is a harbinger of a more severe outbreak.
He said the common belief that severe flu pandemics are preceded by a milder wave of illness arose because of some accounts of the 1918-1919 "Spanish" flu pandemic that killed between 40 million and 100 million people.
