(USA TODAY) -- This year's flu season is starting earlier and hitting harder than it has in almost a decade, the Centers for Disease Control and Prevention says.

"This is at least a month earlier than we would generally see the beginning of the uptick," CDC Director Thomas Frieden said Monday.

Worse, the flu strains circulating in the United States this year, especially the N3N2 version, tend to cause more severe disease, he said.

The good news is that this year's flu vaccine is a 90% match for the circulating strains. "So we're particularly encouraging people who haven't been vaccinated to do it," he said.

The prime flu season is October through April. It usually peaks after the new year -- in January, February or later -- said Melinda Wharton, who directs the CDC's National Center for Immunization and Respiratory Diseases.

One sign the flu season has been launched: More than 2.2% of all visits to the doctor are for flu-like illnesses. In non-flu months, about 1% of doctor visits are for flu-like illnesses. The nation reached the 2.2% threshold last week, said Scott Epperson of the CDC's influenza division.

In some of the hardest-hit states in the South, as many as 4% of doctor visits were for flu-like illnesses.

"Elevated" levels of flu-like illnesses have already been found in five of the USA's 10 regions, according to the CDC's FluView survey.

Alabama, Louisiana, Mississippi, Tennessee and Texas experienced high flu numbers, the CDC said. Much of the Midwest also has elevated numbers.

No special reason for those areas, Wharton said: "Weather is sometimes a possibility, but I think the relationship isn't clear."

Nationally, the percentage of respiratory tests found to be positive for the flu virus during the week ending Nov. 24, the latest report, rose to 15.2% -- higher than usual for this time of year, the CDC said.

A CDC survey found that 6.3% of all people who died that week had the flu or pneumonia -- below what the CDC considers an epidemic rate of 6.7%. No children died that week; there have been two pediatric flu deaths this season.

So far, 112 million Americans have been vaccinated.

Frieden said that expected production of 135 million doses of vaccine means there shouldn not be any shortages.

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