As many as 1.8 million people may end up in the hospital, and 30,000 to 90,000 could die, with a concentration among children and young adults, the presidential panel of the nation's leading scientists said today in outlining what it called a plausible scenario. That's more than twice the annual average of deaths typically associated with the seasonal flu, and those occur mainly in people older than 65.
"We're going to have people hospitalized and we will, unfortunately, have more deaths," said Health and Human Services Secretary Kathleen Sebelius.
The report says this swine flu is a "serious threat to our nation and the world." Because it's a new strain of the flu, people do not have a built-in immunity.
Many swine flu experts view the numbers as reasonable.
"This looks like reasonable estimates and consistent with how pandemic viruses act," said Greg Poland of the Mayo Clinic in Rochester, Minn.
"My reaction is that the numbers, although scary, may be quite accurate," said Joan Nichols of the University of Texas, Galveston.
But others are more skeptical, saying these numbers seem to be a worst-case scenario.
"These speculations have no firm scientific basis, only a historical precedent from almost a 100 years ago and epidemiologic data from recent circulating virus patterns," said UCLA's Peter Katona. "Viruses have a mind of their own, and we will have to just see what happens."
Marc Lipsitch of the Harvard School of Public Health emphasized that the numbers are not predictions, but scenarios.
"It is not possible to predict with certainty how many cases or deaths will occur from this flu," he said.
With 20 weeks left to go in the year, the 2008-09 flu season has 17 more pediatric deaths than the previous year, and there have been at least 7,963 hospitalizations and 522 deaths from swine flu. The CDC says 75 percent of the hospitalizations are in those under 49, and 60 percent of the deaths are also in those under age 49.
The numbers, while higher than usual, are still low. But if the virus spreads throughout the population, it could be far more problematic.
The report says the skyrocketing infections will peak on Oct. 15 -- the exact date a vaccine is expected to be delivered. The White House advisors suggest backing up the vaccine date by a full month -- meaning a vaccine and dosage that is still being tested would be used.
"Trying to rush in with an unknown, with an untested quantity of vaccine doesn't appeal to me at all," said Vanderbilt University's William Schaffner.
The council recommended that manufacturers begin to package the vaccine so that it could be used by those that are at high risk in September. All five manufacturers have already been asked by the government to bottle the vaccine when it's ready.
But health officials announced a delay in the vaccine production last week. Originally, the government expected 120 million doses to be available on Oct. 15, but it now estimates there will only be 45 million, with 20 million more each week through December.
With children heading back to school for the fall, health officials have changed their recommendations for how to deal with students who become infected. They say it's no longer necessary to close an entire school.
In Ft. Worth, Texas, any child with a suspected case of the flu will be isolated in the nurse's office until a parent can pick him or her up. Last year, the superintendent closed all the district's 140 schools and sent 80,000 students home for six days -- all because of one case.
A vaccine is the most effective way to fight the flu, but until it is ready, schools are urging students to wash their hands thoroughly and use hand sanitizer.
The Associated Press contributed to this report.