U.S. health officials say 20 to 40 percent of Americans could become ill from swine flu over the next two years.
That estimate from the Centers for Disease Control and Prevention is twice the number of people who usually get sick in a normal flu season.
Officials said that projection would drop if a planned vaccine campaign and other measures are successful.
Based on the new projections, the number of swine flu deaths over two years could range from 90,000 to several hundred thousand, if efforts to stem the flu failed. The CDC said the estimates are based on a 1957 flu pandemic.