Up to half of the population of the U.S. could come down with the swine flu and 90,000 could die this season, according to a dire report from the President's Council of Advisors on Science and Technology.
The report, which claims as many as 1.8 million people could end up in the hospital seeking treatment for the H1N1 virus, comes as government officials push drug companies to make a vaccine available next month.
"It's a plausible scenario that we need to be prepared for," said Marty Cetron, the Center for Disease Control's director of the Division of Global Migration and Quarantine.
The report says that under a worst-case scenario, between 60 and 120 million Americans could get sick with the swine flu and another 30 million could contract the virus but not show symptoms. Between 30,000 and 90,000 could die -- more than twice the annual average of deaths associated with the seasonal flu. Those deaths generally occur in people older than 65.
The swine flu is "unusual," however, U.S. Health and Human Services Secretary Kathleen Sebelius said, because it tends to affect children and young adults more harshly than others and "hasn't yet affected seniors."
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 Dr. William Schaffner, a professor of preventive medicine at Vanderbilt University.
The council recommended that manufacturers begin to package the vaccine so that it could be used in September by those at high risk. 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.
The report calls the H1N1 virus a "serious threat to our nation and the world."
"We're going to have people hospitalized and we will, unfortunately, have more deaths," Sebelius said.
Many swine flu experts view the numbers as reasonable.
"This looks like reasonable estimates and consistent with how pandemic viruses act," said Dr. Greg Poland, who researches vaccines at the Mayo Clinic in Rochester, Minn.
"My reaction is that the numbers, although scary, may be quite accurate," said Joan Nichols, Ph.D, an associate professor in the department of microbiology and immunology at the University of Texas, Galveston.
But others are more skeptical.
"These speculations have no firm scientific basis, only a historical precedent from almost a hundred 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."
Many colleges are taking steps to prepare their students for a significant spread.
At universities in Louisiana, Colorado, Tennessee and Texas, sick students are being kept in their rooms, given special surgical masks and told not to kiss.
At the University of Kansas, 47 students are already sick with a flu, but it has not yet been cofirmed if it was the H1N1 strain.
ABC News' Dan Childs, David Kerley, Ryan Owens and Sadie Bass contributed to this report.