"We found that only 12 to 42 children need to be vaccinated to directly prevent one outpatient visit for the flu," says Elizabeth Lewis, MD, the study's first author. "And since the vaccination of some children in a preschool or daycare setting also reduces the chance that unvaccinated children would be exposed to the flu virus, the effects of vaccination are probably even greater than we found." Lewis, now with MassGeneral Hospital for Children, worked on the study while at Vanderbilt University Medical School.
The American Academy of Pediatrics recommends that all children between the ages of 6 months and 5 years receive an annual flu shot. Since the specific virus responsible for the flu varies from year to year, determining the preventive impact of influenza vaccination of children has been challenging.
For the current study, the authors analyzed existing data from several sources reporting on flu-related outpatient visits or hospitalizations covering several flu seasons. These included years in which the flu season was relatively mild and well as those in which flu was widespread and caused more serious illness.
Each year's flu vaccine needs to be designed in advance, based on which strains of virus are anticipated to be prevalent in the coming year. Because the accuracy of that prediction varies, the effectiveness of the flu vaccine also varies from year to year. To account for that variation, the research team calculated results based on several potential rates of vaccine efficacy.
"Even in years when only half the immunized children are well protected against flu, vaccination can make a real difference," Lewis says. "I'd advise parents to have their children vaccinated to protect their own health, the health of grandparents and other family members, and the health of other children they are around."