The death toll from a flu outbreak gripping the United States has reached epidemic levels and it will be at least several weeks before the outbreak abates, health officials said Friday.

Flu or pneumonia were responsible for 7.3 percent of the deaths reported in 122 cities monitored by the Centers for Disease Control and Prevention (CDC) for the week ending January 5. That's just above the epidemic threshold of 7.2 percent.

"Most of the country is seeing or has seen a lot of flu," CDC director Tom Frieden said in a conference call.

"Only time will tell us how long our season will last or how moderate or severe it will be."

Frieden urged people to get protect themselves against the flu with a vaccine, which this year appears to be about 62 percent effective.

"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 cautioned.

There are some indications that the outbreak may have peaked in some areas, but 47 states are still reporting widespread flu activity, Frieden said.

The number of states reporting a high level of flu fell to 24 from 29 states and the number of states reporting moderate levels rose to 16 from nine.

Flu strikes every year across the United States, bringing chills, fever, coughing and achy misery to millions.

The number of annual deaths has ranged from a low of 3,000 to a high of 49,000 since 1976, according to the CDC.

Most of those deaths are among people aged 65 and older.

Some 20 children have died so far this season, up from 18 in the CDC's previous weekly report. It does not collect data on the number of adult flu deaths in real time.