NEW YORK » Flu season is off to its earliest start in nearly 10 years — and it could be a bad one.

Health officials today said suspected flu cases have jumped in five southern states, and the primary strain circulating is one that tends to make people sicker, especially the elderly.

"It looks like it’s shaping up to be a bad flu season, but only time will tell," said Dr. Thomas Frieden, the director of the Centers for Disease Control and Prevention.

The good news is the nation seems to be fairly well prepared, Frieden said. More than a third of Americans have been vaccinated, and the vaccine is well matched to the strains of flu seen so far, CDC officials said.

Higher-than-normal reports of flu have come in from Alabama, Louisiana, Mississippi, Tennessee and Texas. An uptick in flu cases like this usually doesn’t occur until after Christmas.

It’s not clear why the flu is showing up so early. But flu-related hospitalizations are rising earlier than usual, and there have already been two flu-related deaths in children.

In fact the last time a typical flu season started this early was the winter of 2003-04. That also happened to be a year when the dominant flu type was the same one seen most widely this year. And in that year, there were a higher-than-usual number of flu-related deaths in both the elderly and children.

One key difference: In 2003-04, the flu vaccine was a poor match to the flu strain.

Another: There’s more vaccine now, and flu vaccination rates have risen for the general public and for key groups like pregnant women and health care workers.

In all, an estimated 112 million Americans have been vaccinated so far, the CDC said. Flu vaccinations are recommended for everyone who is 6 months of age or older.