Children under the age of 5 who receive an annual flu shot have a greatly reduced risk of needing to see their doctor or be admitted to the hospital because of flu-related illness. A new study in the September issue of Pediatrics that analyzes how many outpatient visits or hospitalizations might be prevented by childhood influenza immunization finds that vaccinating only half U.S. children could eliminate as many as 650,000 doctor's office visits and 2,250 hospitalizations in a year.
"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."
The co-authors of the Pediatrics report are principal investigator Katherine Poehling, MD, MPH, now at Wake Forest University School of Medicine; Marie R. Griffin, MD, MPH, Kathryn M. Edwards, MD, Yuwei Zhu, MD, MS, of Vanderbilt University Medical Center; and Peter G. Szilagyi, MD, MPH, University of Rochester School of Medicine and Dentistry. The study was funded by the Robert Wood Johnson Foundation and the National Institutes of Health.
Massachusetts General Hospital (www.massgeneral.org), established in 1811, is the original and largest teaching hospital of Harvard Medical School. The MGH conducts the largest hospital-based research program in the United States, with an annual research budget of more than $500 million and major research centers in AIDS, cardiovascular research, cancer, computational and integrative biology, cutaneous biology, human genetics, medical imaging, neurodegenerative disorders, regenerative medicine, systems biology, transplantation biology and photomedicine.