Virus of the year. The novel H1N1 influenza.

For years, scientists have been warning about the potential for an influenza pandemic on the order of the 1918 Spanish flu. They imagined the culprit would surface in Asia—and, since 2003, have worried that the avian influenza strain H5N1 might be it. Health officials worldwide drafted one preparedness plan after another. But the pandemic that erupted last spring looks nothing like the one in the plans. Not only did it begin in North America, but the swine virus behind it is a novel form of an H1N1 strain already circulating in humans. And although the new H1N1 is unusually dangerous for the young and for pregnant women, in most otherwise healthy people it causes a disease no more severe than seasonal flu. Scientists have repeatedly warned that this relatively mild virus could mutate or swap genes with cousins and become deadlier. But for now, it looks as if this H1N1 will go down in history more for causing confusion than catastrophe.