Recommendations for vaccination changed over the period, but since 2008, the C.D.C. has recommended a flu shot for everyone 6 months or older.
Of the 511 children whose vaccination status was known, 84 percent had not had a flu shot. In the 2009-10 flu season, when 66 children with a known vaccination status died, 64 of them were unvaccinated.
Death often came quickly: most of the children died within a week of the appearance of symptoms, and a third of them died outside the hospital or in an emergency room.
"A lot of parents don't think of flu as being very serious, especially if their child is healthy" said the lead author, Dr. Karen K. Wong, a medical officer with the C.D.C. "But this study shows that even healthy children are at risk, and that's why it's important for every child to get vaccinated."
Image: Baby receiving a flu shot, via Shutterstock