The global flu pandemic expected to return to the USA this fall may infect as much as half the U.S. population, flooding hospitals with nearly 2 million patients and causing 30,000 to 90,000 deaths, according to the first official forecast of the scope of the flu season now beginning.

The report, released Monday by the White House, was prepared by the President's Council of Advisors on Science and Technology. It offers the forecast as the most plausible of a range of scenarios that reflect the potential effect of a new form of H1N1 flu, known as swine flu, which the report calls "a serious health threat to the United States."

"While this is not the 1918 flu pandemic, it infects younger people more, and serious complications do occur," says panel Co-chairman Eric Lander, director of the Broad Institute of Harvard and MIT. He warns that infants and children, pregnant women and people with chronic illnesses are at special risk of serious complications.

The Centers for Disease Control and Prevention estimates that nearly 2 million people nationwide have been infected with the virus and that 522 have died. Flu experts worry that cases will mount as youngsters return to school and as cold weather drives people indoors. "We think it's very likely cases will increase," says David Marens of the National Institute of Allergy and Infectious Diseases.

One of the council's goals was to use scenarios drawn from experience to identify health concerns and guide the government's response. The report concludes that the coming flu season will more likely resemble 1957, which killed 70,000 people, or 1968, when 34,000 died. The 1918 pandemic killed hundreds of thousands in the U.S.

"There's great uncertainty about what we're going to be seeing as this develops," says White House homeland security adviser John Brennan.

The report calls for the government to intensify efforts to track infections and hospitalizations and to advocate common-sense prevention. Among them: making sure that sick people can get refunds to sporting events and that sick children who rely on school lunches can get them without infecting classmates.

The science advisers also urge the government to press vaccine makers to speed production by one month by beginning to fill and distribute vials before clinical trials are completed. Without accelerating vaccine production, they say, the first doses may not become available until after the swine flu season peaks. In response, the government has asked manufacturers to put vaccine in vials "as soon as they are ready," the administration says.

The report asserts that an influx of flu patients may clog hospital emergency rooms and intensive-care units. "It's possible that at a time of peak demand, 50% to 100% of ICU beds in an area might be used for influenza cases," Lander says. "They're often close to capacity without influenza."