How severe is swine flu?

The severity of cases in the current swine flu outbreak has varied widely. In Mexico, there have been deaths and other severe cases. Early cases in the U.S. have been mild. But that could change. The virus itself could change, either becoming more or less dangerous. Scientists are watching closely to see which way the new swine flu virus is heading — but health experts warn that flu viruses are notoriously hard to predict, as far as how and when they'll change.