Experts are divided over the likelihood of a swine flu resurgence: Some think there will be many more cases, while others don't predict a return, Frieden said. "Others think we don't know. That's probably the most accurate thing to admit. Only the future will tell what the future brings," he said.
The H1N1 swine flu continues to strike children and young adults the hardest, probably because it's been more than a half century since the H1N1 virus was at a pandemic level, leaving younger people with little or no immunity to the current strain. The CDC estimates that from April, when the swine flu first appeared, to the middle of November, 47 million Americans had come down with the virus. The good news is that the illness continues to produce mild-to-moderate symptoms in most people and recovery usually takes about a week.
Over the same eight months, nearly 10,000 people died from the H1N1 flu -- the majority of them children and young adults -- and 213,000 people were hospitalized, Frieden said.
"This has been a strain of influenza that's been much harder on children and young adults," Frieden said Friday. "In fact, the number of children and young adults killed through mid-November was five times more than an average flu season."
During a normal flu season, the seasonal flu typically causes about 36,000 deaths and 200,000 hospitalizations, mostly among people 65 and older.
CDC spokesman Jeff Diamond said that, as of late last week, H1N1 swine flu still made up a vast majority of the circulating flu, with seasonal flu accounting for only a very small percent of flu cases.
But Diamond said it's too early in the seasonal flu season to predict what will happen, and he urged people to get a seasonal flu shot.
To learn more about flu, visit the U.S. Department of Health and Human Services.
SOURCES: Terry Nolan, M.B.B.S., Ph.D., professor and head, Melbourne School of Population Health, and Department of Public Health, University of Melbourne, Australia; Marc Siegel, M.D., associate professor, medicine, New York University, New York City; Jeff Diamond, spokesman, U.S. Centers for Disease Control and Prevention