During influenza epidemics, rates of attack may exceed 40 percent in preschool children and 30 percent in school-age children. Children are primary carriers of influenza virus and introduce the infection to many households where it spreads to adult members. Influenza vaccination, however, is not routinely recommended in children, other than in those with risk factors such as respiratory or cardiopulmonary disease. To investigate morbidity from influenza in children, Neuzil and colleagues performed a retrospective study of respiratory and other pertinent illnesses during 19 influenza seasons in otherwise healthy children less than 15 years of age.

The authors reviewed Medicaid files for 1973 through 1993. Data were collected on children at low risk of influenza-related complications. Excluded were children considered to be at high risk, such as those with a birth weight of less than 2,500 g (5 lb, 8 oz), chronic cardiac, renal or pulmonary disease, immune deficiency, sickle cell disease, chronic use of steroids, diabetes and cancer. Low-risk children accounted for 91 percent of the group, providing 2,035,143 person-years in which data were examined.

The children were divided into five groups according to age: (1) less than six months, (2) six to 12 months, (3) one to three years, (4) three to five years and (5) five to 15 years. The influenza period was defined as November 1 to April 30. The primary outcomes for the analysis were hospitalization for or death from pneumonia, acute respiratory conditions other than pneumonia or influenza, nonacute respiratory conditions other than pneumonia or influenza, heart failure or myocarditis. Secondary outcomes were the number of outpatient visits and the number of antibiotic prescriptions.

There were 46,690 hospitalizations for acute cardiopulmonary conditions during the study period; 28 percent occurred during an influenza season. In all age groups, the rate of hospitalization was higher during the influenza season than during other times of the year. The highest hospitalization rate in all seasons was among children less than six months of age. In this age group, the average excess number of hospitalizations for cardiopulmonary conditions attributable to influenza was 103.8 per 10,000 children annually. Among children six to 12 months of age, the excess number of hospitalizations attributable to influenza-related cardiopulmonary conditions was 49.6 per 10,000 annually. In children five to 15 years of age, the excess hospitalization rate was 4.1.

Data also revealed an excess of office visits and antibiotic prescriptions for all age groups during the influenza season, with the largest number occurring in the age group of six to 12 months. Influenza was found to account for 19, 18 and 20 percent of the excess number of hospitalizations in the winter for children less than six months, six to 12 months and one to three years of age, respectively. In children less than six months, influenza accounted for 10 percent of the excess number of antibiotic courses in the winter. In children six to 12 months of age, it accounted for 14 percent of the excess number of antibiotic courses. In children one to three years of age, influenza accounted for 20 percent of the excess number of courses of antibiotics.

The authors conclude that influenza-related conditions account for a large number of hospitalizations, office visits and courses of antibiotics in young children. The greatest risk appears to be in children less than 12 months of age. The authors believe consideration should be given to administering influenza vaccine in otherwise healthy children. However, issues of cost, safety, efficacy and ease of administration must be assessed before a change is made in the national immunization policy.

editor's note: In the same issue of the New England Journal of Medicine, findings from a study by the Centers for Disease Control and Prevention (CDC) are reported. The CDC study also revealed that hospitalization rates were significantly increased during influenza outbreaks, especially in children less than two years of age. Both articles advocate clinical studies to assess the safety and efficacy of influenza vaccine in healthy children. An accompanying editorial does the same but also raises concerns about vaccine safety, noting the recent problem with the rotavirus vaccine, and poses the question of whether the majority of respiratory infections were due to influenza or to respiratory syncytial virus or other viral pathogens. Nonetheless, the data are compelling, and the utility and value of yearly influenza immunization in children should be investigated on a national level.—j.t.k.