WASHINGTON, D.C. ? Most young children who are sick with the flu do not get properly diagnosed or fully treated for that serious viral infection – even after a visit to the doctor’s office or the hospital – according to newly published research.

The results were shared in advance with officials at the federal Centers for Disease Control and Prevention, and helped persuade the government to change its recommendations for flu shots this year to include children ages 2 to 5.

The old recommendation had been to vaccinate only children younger than 2, in part because it was unclear how prevalent the flu was in preschoolers.

For four years, Katherine Poehling of Vanderbilt University Medical Center and her colleagues performed nasal swabs on children who arrived at doctors’ offices or emergency rooms with runny noses, fever and other flu symptoms. As expected, about 80 percent of those who tested positive for the influenza virus were children younger than 2.

But one of every six children up to age 5 with flu symptoms tested positive during “moderate” flu seasons. Even during “mild” flu seasons, one in 16 tested positive.