Flu season in the United States is off to its earliest start in nearly a decade — and it could be a bad one.

Health officials on Monday said suspected flu cases have jumped in five Southern states, and the primary strain circulating tends to make people sicker than other types. It is particularly hard on the elderly.

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

The good news is that the nation seems fairly well-prepared, Frieden said. More than a third of Americans have been vaccinated, and the vaccine formulated for this year is well-matched to the strains of the virus seen so far, CDC officials said.

Higher-than-normal reports of flu have come in from Alabama, Louisiana, Mississippi, Tennessee and Texas. An uptick like this usually doesn’t happen until after Christmas. Flu-related hospitalizations are also rising earlier than usual, and there have already been two deaths in children.