NBCNEWS.COM - Flu activity remains high across the United States, but there are signs this year's bad season may be waning in some areas, government health officials said Friday.
Forty-seven states reported widespread flu activity as of the week ending Jan. 5, up from 41 the previous week. Twenty-four states and New York City reported high levels of flu-like illness, but that was down from 29 states and NYC the week before, according to new data released by the Centers for Disease Control and Prevention.
Still, flu is unpredictable and illness could rebound or worsen, said CDC Director Dr. Tom Frieden.
"Truly, only the next week or two will show whether we have, in fact, crossed the peak," Frieden told reporters in a conference call. "Nationally, it's likely that influenza will continue for several more weeks."
Flu activity was elevated all across the U.S., except in the region that includes Arizona, California, Guam, Hawaii and Nevada, the new report showed.
More than 3,700 people have been hospitalized for the flu since October, and 20 children have died, the CDC says. Most of the hospitalizations have been in people older than 65.
Vaccines given to fight this year's flu appear to be about 62 percent effective overall , according to data from some 1,155 children and adults with acute respiratory infections. Of people who got the flu, 32 percent were vaccinated. CDC officials characterize that level as "moderate" effectiveness and infection control experts say it's about what they expect from the shots.
"That's normal," said Dr. William Schaffner, chairman of the department of preventive medicine at Vanderbilt University in Nashville, Tenn. "It's a good but not a perfect vaccine."
This year's vaccines appear to be about 55 percent effective against influenza A strains, which are responsible for most illness and more severe cases, and about 70 percent effective against influenza B, which is usually less serious, the report showed.
That helps explain why some people who've received flu shots -- which are recommended for everyone older than six months -- say they've still gotten sick. It argues in favor of using antiviral drugs such as Tamiflu to help bolster vaccine effectiveness, or VE, CDC's report said.
"These early VE estimates underscore that some vaccinated persons will become infected with influenza; therefore, antiviral medications should be used as recommended for treatment in patients, regardless of vaccination status," the report concluded.