CHICAGO (CBS) — New numbers out from the CDC showed a spike in flu cases is just starting nationwide.

The young are particularly vulnerable this year.

Children arrived at Dr. Dan Weissbluth’s office for an ear inflection. But the Chicago pediatrician said his office has seen a steady number of kids with flu so far this season.

“We’re seeing children anywhere from six months up to 15 or 16 years of age who show in our office who been diagnosed with flu,” Weissbluth said.

Health officials said this season’s flu strain is particularly targeting children. The Centers of Disease Control reported 13 children have died nationwide, including one in Illinois.

“Among hospitalizations so far this year, the highest rates that we are seeing are in those who are under age five,” said Daniel Jernigan of the CDC.

“The flu season is just starting to heat up,” said Cook County Health System’s Dr. David Schwartz.

The flu season typically starts in November or December, but is starting later this year. Schwartz is the chairman of the infectious diseases department for the Cook County Health System.

“The numbers of diagnosed cases is increasing in the last several weeks,” Schwartz said.

Both doctors Schwartz and Weissbluth recommend children over six months get flu shots.

“In our practice every patient that has had the flu shot so far has not been diagnosed with the flu, subsequently,” Weissbluth said. “Getting the flu shot is not a 100% guarantee that your child will not get the flu. But you’re doing the best you can to reduce the risk of getting the flu.”

Doctors said with many weeks left in the flu season,  it is not too late to get the flu shot. Last year’s flu season was the deadliest in 40 years.