The spread of the flu across the United States appears to have slowed in some areas, but officials won't know for weeks whether the cases have peaked, the CDC director said Friday.

Twenty-four states and New York City were reporting high levels of flu activity, according to the Centers for Disease Control and Prevention's flu advisory report for December 30 through January 5. That's down from 29 states the previous week, said Dr. Thomas Frieden, director of the CDC.

However, "The only area of the country that's still relatively unaffected ... is the far West Coast," although plenty of cases have been reported there, Dr. Joseph Bresee, chief of the Epidemiology and Prevention Branch of the CDC's Influenza Division, said Friday.

The number of pediatric deaths associated with influenza rose by two, according to the CDC.

There have been 20 deaths of people under the age of 18 since the flu outbreak began. While the CDC does not count the number of adult deaths related to the flu, some states do, and that data suggests dozens have died.

According to the latest CDC activity map, flu levels dropped in several states, particularly in the Southeast, including Georgia, Florida, South Carolina, Arkansas and Kentucky. In the Northeast, levels in some states have also improved, such as New York, but New York City remains among the areas of high activity.

The number of states reporting widespread activity, however, increased to 47 from 41, according to the CDC's flu advisory report. The only states without widespread activity are California, Hawaii and Mississippi.

"Widespread" means that more than 50% of geographic regions in a state -- counties, for example -- are reporting flu activity. It addresses the spread of the flu, not its severity.

"Bottom line: It's flu season," Frieden told reporters. Flu activity is "elevated" in most of the United States, he said, and "it may be decreasing in some areas, but that's hard to predict ... influenza activity ebbs and flows."

Officials will know in the next couple of weeks whether the season has peaked, he said. "The only thing predictable about the flu is, it's unpredictable."

"... We are into what would classically be described as a flu epidemic," Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases at the National Institutes of Health, told CNN's Wolf Blitzer on Thursday.

"It's still on the uptick," he said.

"Remember, once it peaks, you still have a considerable amount of time where there is a lot of flu activity, and right now it may have peaked in some places, but for the most part, it has not yet peaked," Fauci said.

Many reports of emergency rooms and clinics being overwhelmed with patients could be linked to other illnesses, too. This is also a prominent season for many other respiratory viruses, Bresee said. Norovirus, which causes diarrhea and vomiting, has also been circulating.

Vaccination

Although the flu vaccine is far from perfect, it's the best prevention tool we have, Frieden said. You can still get it -- it's better late than never.

The flu vaccine is about 62% effective, Frieden said.

"The 62% -- we'd love it to be better, but it is actually a substantial public health benefit for the population," Bresee said.

Based on vaccine coverage surveys, 37% of Americans had been vaccinated by mid-November, CDC officials said. That's about on track with what was seen at this time last year.

"We have seen a lot of vaccination happening in the last couple of weeks," Bresee said. "I don't know where we'll end up this year."

Vaccine manufacturers told CNN on Thursday that there is plenty of vaccine for those who want to get a flu shot.

However, there are reports of spot shortages of the vaccine, Frieden said, so call your provider ahead of time if you still want to get the vaccine.

"You may have to check in several places to find the vaccine, because most of the more than 130 million doses that were produced by vaccine manufacturers this year have already been given," he said.

Early flu season

The flu came early this season, and cases are more severe than last year, health officials say.