Forty-eight states reported widespread influenza infections last week, according to the U.S. Centers for Disease Control and Prevention.
CDC Director Dr. Tom Frieden described this year as a "worse than average season, particularly for the elderly."
"Many parts of the country are still seeing high - and in some parts - increasing levels of activity while overall activity is beginning to go down," Frieden said in a teleconference.
This year's flu season has reached the midpoint, which means new cases of flu are beginning to fall, but Frieden said he expects both the number and rates of hospitalization and death to rise further as the flu epidemic progresses.
Thousands of people die every year from flu, but the elderly generally are the hardest hit, with 90 percent of all flu deaths occurring in people over age 65.
The CDC does not keep track of all flu-related deaths in adults, but during the second week of January, 8.3 percent of deaths reported to its 122 Cities Mortality Reporting System were due to pneumonia and influenza. That is up from 7.3 percent reported the previous week and exceeds the epidemic threshold of 7.2 percent.
In the first two weeks of January, nine children died of complications from the flu, bringing the death toll of children from this year's flu season to 29, the CDC reported.
That compares with a total of 34 child deaths for the entire 2011-2012 flu season, an especially mild one, and 282 during the severe 2009-2010 season.
Last week, the percentage of visits to healthcare providers for flu-like illness fell to 4.6 percent, down from a revised 4.8 percent in the prior week, the CDC said. By comparison, in the 2009 H1N1 "swine" flu pandemic, 7.7 percent of visits were for flu-like illness.
TAMIFLU IN SHORT SUPPLY
Despite continued reports of spot shortages, Frieden said it is not too late to get vaccinated.
Flu vaccine makers had expected to produce 135 million doses of vaccine, but they have been able to eek out an additional 10 million doses. So far, Frieden said, 129 million doses have been made available for distribution to doctors' offices, drug stores, clinics and other facilities.
"That means there is more vaccine out there for suppliers to order," he said.
To avert shortages of the antiviral drug Tamiflu, made by Roche Holding AG's Genentech unit, Food and Drug Administration Commissioner Dr. Margaret Hamburg said her agency has authorized the company to distribute 2 million doses of a 75 milligram capsule from its stockpile that contains an older version of the package instructions.
"This medication is fully approved. It is not outdated," she said. "To assure people have access, we took the necessary steps to allow Genentech to distribute its reserve without requiring them to repackage it, which would have taken months," Hamburg said.
Last week, Roche said the liquid form of Tamiflu, which is given to children who already have the flu to alleviate symptoms, was in short supply.
At the time, Roche said it had warned wholesalers and distributors that temporary delays in shipments were imminent.
Pharmacists can make a substitute by dissolving Tamiflu capsules in a sweet liquid.
(Reporting by Julie Steenhuysen; Editing by Vicki Allen and Eric Beech)