The new estimates mean about 1 in 6 Americans have had the illness. The figures were released by the Centers for Disease Control and Prevention on Thursday.
The CDC also estimates that 200,000 people have been hospitalized since the virus was first identified in April though mid-November. That's the same amount that occurs normally in an entire flu season.
The CDCthat H1N1 flu (also known as swine flu) infections seem to be dropping though the number of children who died with the illness was higher.
Previously, the CDC estimated that about 22 million people came down with H1N1 from April to mid-October, reports CBS News medical correspondent Dr. Jon LaPook. In the space of four weeks, that number jumped to 47 million, the vast majority under age 65.
Children and young adults have been one of the hardest-hit groups. An estimated 1,100 children have died from H1N1.
"Many times more children and younger adults, unfortunately, have been hospitalized or killed by H1N1 influenza than occurs during a regular flu season," said CDC Director Tom Frieden.
In a typical flu season, about 20,000 children are hospitalized. Already in the first seven months of the H1N1 outbreak, 71,000 have been hospitalized, LaPook reports.
The H1N1 flu pandemic has so far hit in two waves in the United States: First in the spring, then a larger wave that started in the late summer.
In late October, 48 states reported widespread flu activity. Increasingly, that appears to have been the peak of the second wave. Since then, fewer states have been reporting widespread cases, and the number of school closings due to swine flu has at times dropped to zero.
Since November, new infections seem to be receding, but the CDC is urging people not to forget about immunization. Last month at the Dallas County Health Department, 3,000 people poured in daily for vaccine. That's now down to a trickle.
Dr. John Carlo is worried the virus isn't done yet.
"We're really going to be concerned about what the rest of the winter is going to be like," Carlo told LaPook. "We have to be ready for what's going to happen in February and March."
CDC officials also said Thursday that American Indians and Alaska Natives have died from swine flu at a rate four times greater than other Americans.
In a study of swine flu deaths in 12 states, researchers found that 42 American Indians and Alaska Natives in those states died of swine flu or its complications. That was a rate of nearly 4 out of every 100,000 people in that group.
American Indians and Alaska Natives have higher rates of diabetes, asthma and other conditions that make them more vulnerable. The study is being published in the CDC's Morbidity and Mortality Weekly Report.