Is the U.S. H1N1 epidemic over? Federal health officials won't go so far as to day that, but on Friday they reported for the fourth week in a row that no states had widespread flu activity.

U.S. cases have been declining since October. An official with the Centers for Disease Control and Prevention says H1N1 cases are still occurring and are likely to continue a while longer at some level.

But another expert said a future large wave of cases now seems very unlikely. The expert, Vanderbilt University's Dr. William Schaffner, said the epidemic has "one foot in the grave."