A recent case of seemingly healthy 17-year-old girl who died after being struck with the flu shows just how deadly the disease can be.

Shannon Zwanziger hadn’t needed to go to a doctor in three years, but she died just after just a week of coming down with the flu, part of what the Centers for Disease Control and Prevention are calling an epidemic due to 15 children dying since Dec. 20, a number that is expected to go up, according to a CNN report.

The flu season typically begins in the early fall and persists until May, making it still fairly early in the flu season.

Zwanziger passed away on Dec. 9. Before then, she had become so week she had to slide down each step in order to make her way down the stairs to take a bath, but her mother noticed her eyes and worried that she’d made a mistake, according to a CNN. She tried to lift her out of the bath, but she “passed away in my arms.”

Although she hadn’t actually died yet, Zwanziger never did regain consciousness. Mouth-to-mouth resuscitation did no good, and the family frantically called 911. She had a slight heartbeat at the hospital, but that ceased a few hours later.

Zwanziger had first gone to a clinic at the hospital when she came down with the illness. She was told it was the flu and she should rest and recuperate at home.

But what Zwanziger’s family didn’t know at the time was that she had typa A flu, which caused her liver to give out at some point during her stay at home.

Her mother urged people to get blood tests if they are suffering from symptoms.

Zwanziger had not had the flu vaccine. She was allowed to choose whether to have a flu vaccine, and she chose not to, although it is not known whether a vaccine would have helped in this case.

The CDC is calling this an unusually bad year for the flu vaccine, which has not done a good job of preventing many of the strains that were tested. At the core of the issue is a mutated strain that developed before this most recent vaccine was developed.