In a typical year, about 10% of Americans get the flu. Although many people think of the flu as a mild ailment, each year in the United States a couple of hundred thousand people get sick enough to require hospitalization, and between 20,000 and 40,000 die from the infection.

Already, 2009 is not a typical year. We're in the midst of a flu pandemic caused by a virus that first emerged in Mexico in mid-February. Billions are being spent on preparedness plans. And millions of Americans may line up in the fall to get two kinds of flu vaccines, one for the regular seasonal flu that comes around every winter and another for the pandemic strain.

So far, the 2009 pandemic has been more widespread than lethal. Only about a thousand deaths have been reported worldwide, including about four hundred in the United States, and it didn't get appreciably more deadly during the peak flu season in the Southern Hemisphere in June, July, and August. Flu experts believe the virus has some properties that may make it inherently less pathogenic — that is, less capable of causing serious disease — than other strains.More »