A 10th child has died from the flu this year, prompting state health officials to say this flu season may be the worst in years.
Nine people under the age of 18 died in the H1N1 pandemic in 2009, according to the Minnesota Department of Health.
• Earlier: Flu claims a ninth child in Minnesota
Kris Ehresmann, who directs the department's infectious disease division, said the nearly 4,000 influenza hospitalizations for all ages exceeded the state's highest levels by almost a thousand. During the 2012-13 season, 3,068 were hospitalized.
Children's Hospitals and Clinics of Minnesota treated eight of the 10 children who died. Patsy Stinchfield, infection control director, said the vaccine wasn't as effective as in years past.
"What came here, the Influenza A, was not matched well for what was in the vaccine," she said.
Stinchfield said the nasal version of the flu vaccine also did not work as well.
Finally, the spread of infection was high, and included school outbreaks.
"Our emergency rooms here at Children's, our clinics, were extremely busy this year, and broke emergency room records," Stinchfield said.
She said Children's processed a record-setting 1,277 positive flu tests between Oct. 1, 2014, and April 18.
While flu type AH3 contributed to a huge spike in infections at the end of last year, Ehresmann said the type of flu sickening people changed during the season.
"It's sort of a combination of a very bad season for Influenza A, along with an ongoing second peak with Influenza B," Ehresmann said.
Seven of the pediatric deaths were caused by Influenza A; three were caused by Influenza B.
While the state doesn't track flu-related deaths in all age groups, Karen Martin, an epidemiologist with the state health department, said older Minnesotans suffered greatly.
"By far the 65-and-older have been the most affected with influenza and that's very typical of an influenza season, particularly if the dominant strain is an H3 strain, as it was this year," she said.
According to state health department data, seniors accounted for more than half of all flu hospitalizations this season.
Pitrish Tosh, an infectious disease physician at Mayo Clinic, said the severity of flu season points to a larger issue.
"In the end, the real push needs to be on better vaccine development," Tosh said. "Even in a great year, the vaccine efficacy is going to be around 70 percent among healthy people. Although that's pretty good, it's not 100 percent."
Still, Ehresmann stressed it's important to get vaccinated. That goes for children, too.
"Some of these kids were absolutely healthy kids," she said. "So we cannot minimize the value of vaccination and like I said, we know it's not as effective as we'd like it to be, but even if it were only 20 percent effective that could have potentially saved two lives, and that is worth it."
The flu season typically lasts until late April or early May.