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So far this season,105 children have died from the flu, according to data released Friday by the US Centers for Disease Control and Prevention. This is the highest number of child flu deaths at this point in the season since the CDC started keeping records in 2004, except for the 2009 flu pandemic.

It has been an “unusual” flu season with a higher proportion of children and young adults affected than the older population, according to Dr. William Schaffner, an infectious disease specialist at Vanderbilt University Medical Center.

The earlier prevalence of influenza B – a flu strain that tends to be more common in children – could be a reason why more children were affected, Schaffner said. Also, as the number of influenza B cases decreased, the number of H1N1 cases increased, he said. H1N1 is a subtype of the influenza A strain, which also affects children more than adults.

“This is the first time in 25 years where [influenza B] became so common so early,” said Dr. Buddy Creech, an associate professor of pediatric infectious diseases at Vanderbilt University Medical Center.

Neither Schaffner nor Creech know why this year’s influenza timeline is so different.

“It’s leaving all influenza virologists puzzled,” Schaffner said.

That earlier influenza B peak may be one reason why there are more pediatric flu-related deaths than usual, according to Schaffner.

Also, influenza B can present with unexpected symptoms, so parents might not seek care right away, according to Creech.

“Often influenza B is more likely to cause gastrointestinal symptoms than influenza A, though both can in young children,” he said. “Some parents don’t recognize these symptoms as part of influenza … which may delay thinking of influenza and delay treatment.”

Gastrointestinal symptoms, such as vomiting, can also impact one’s ability to take antivirals that can shorten the flu’s duration, he said.

Another reason for the higher number of flu-related deaths in children might not be specific to kids at all.

“It could just be a reflection of a particularly severe season,” said Dr. Arnold Monto, a professor of epidemiology at the University of Michigan School of Public Health. Monto noted that there are many flu-related deaths among children every year in the United States.

He agreed that it’s an odd season that may last longer.

“We may have the flu going into April this year because it’s still going strong right now,” he said.

Given the uncertainty about how long this flu season will last, Monto recommended getting an influenza vaccine, explaining that the children who die from the flu are more likely to be the ones who weren’t vaccinated.

The CDC said this week it considers the current flu shot to be “substantial protection” for children ages 6 months to 17 years old.

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Schaffner also said everyone should get vaccinated, especially since the flu can strike a perfectly healthy individual and cause severe illness. At least half of the children who die from the flu were otherwise healthy, he said.

“[The vaccine] may not prevent the illness completely,” Schaffner said, “but if you’re vaccinated and you still get the flu, you’re more likely to have a less severe infection … Your risk of dying is less.”

CNN’s Scottie Andrew, John Bonifield and Jen Christensen contributed to this report.