Influenza Infections in Children 

Abstract & Commentary

Synopsis: Influenza vaccination of healthy children is necessary to prevent the majority of influenza-associated pediatric morbidity and mortality.

Source: Peltola V, et al. Influenza A and B virus infections in children. Clin Infect Dis. 2003;36:299-305.

A retrospective study of children treated at a tertiary referral hospital in Finland from 1980 through 1999 identified 683 of 15,420 children with influenza that was confirmed by direct antigen detection in nasopharyngeal aspirates. There were 544 cases of influenza A, with a median age of 2.0 years, and 139 cases of influenza B, with a median age of 4.2 years. One-fourth of children with influenza had an underlying medical condition. Most children with influenza A or influenza B had high fever (94% and 89%, respectively), with febrile convulsions in 12% and 9%, respectively. Cough and rhinorrhea occurred in 89% and 94%, respectively, of children with influenza A, but only 60% and 67%, respectively, of children with influenza B. Children with influenza A were more likely to be ill-appearing, 10% vs 4% (P = .021). Leukopenia (< 4.0 × 109 WBCs/L) occurred in 8% of children with influenza A and 19% of children with influenza B; leukocytosis (> 15.0 × 109 WBCs/L) occurred in 8% overall. Complications included otitis media in 24% and pneumonia in 9%.

Comment by Hal B. Jenson, MD, FAAP

There has been increased awareness of the importance and severity of influenza infections among young children. This study characterizes the epidemiology and clinical presentation of influenza in children during 20 seasons. Influenza A predominated, causing 80% of infections overall and was the predominate type in 15 of 20 influenza seasons during the study period. Influenza A infections were more tightly clustered temporally, with 90% of annual diagnoses during a 60-day period around the peak of the annual outbreak, whereas influenza B infections occurred on a more irregular basis. Although the highest incidence for both was in children younger than 1 year (27% of cases of influenza A and 24% of cases of influenza B), there was a faster age-related decrease in the incidence of influenza A than influenza B.

Distinguishing influenza from other viral infections in children on the basis of clinical findings remains difficult. Antigen testing is necessary for clinicians to identify those children with influenza from among the other causes of febrile illnesses in children.

One-fourth of children hospitalized with influenza had an underlying medical condition (eg, asthma, neurologic deficits, or malignancies). Although increased rates of hospitalizations of children with chronic medical conditions are recognized during influenza season, the majority of hospitalized children were previously healthy. These hospitalizations would not be prevented with influenza vaccination programs targeted only to high-risk children. Recently, the US Advisory Committee on Immunization Practices recommended influenza vaccination for healthy children aged 6-23 months "when feasible." This study confirms the necessity of including previously healthy children in influenza vaccination programs. Not only will such a strategy decrease influenza-associated morbidity and mortality among young children, but it should also decrease the influenza burden among the adult population because of the important role of young children in community transmission of influenza.

Dr. Jenson is Chair, Department of Pediatrics, Director, Center for Pediatric Research, Eastern Virginia Medical School and Children's Hospital of the King's Daughters, Norfolk, VA