Even healthy children can come down with a case of flu severe enough to kill them in a matter of days, according to a new report from researchers at the U.S. Centers for Disease Control and Prevention.

Children who were in good health before contracting influenza seemed to progress from infection to death more rapidly than children with high-risk medical conditions, the researchers reported in a study published Monday in the journal Pediatrics.

The finding is based on the first analysis of all flu deaths among children since the National Notifiable Diseases Surveillance System began tracking such cases in October 2004. In the eight years through September 2012, there were 830 laboratory-confirmed deaths from flu.

In 794 of those cases, the researchers were able to check the patients’ medical histories. They found that 341 of those victims – 43 percent – did not have a medical condition that would have made them more vulnerable to influenza.

Public health officials take influenza seriously because it’s easy for people to reduce their risk of infection by getting flu shots. CDC officials reported last month that 43 percent of children weren’t vaccinated during the 2012-13 flu season, along with 58 percent of adults.

The researchers were able to find the vaccination records for 511 of the children in the study. Only 16 percent “had been fully vaccinated with seasonal influenza vaccine,” they reported.

To put the 104 annual flu deaths into perspective, the CDC said there were 9,595 deaths among children ages 1 to 14 in 2010.