Childhood influenza: number needed to vaccinate to prevent 1 hospitalization or outpatient visit

The goal was to assess the potential benefits of the influenza vaccine recommendations for children 6 to 59 months of age by estimating the number of children needed to be vaccinated to prevent 1 hospitalization or 1 outpatient visit attributable to influenza.

The influenza burden was obtained from published studies in which rates for children 6 to 23 months and 24 to 59 months of age could be ascertained. We assumed a range of influenza vaccine efficacies of 25% to 75%, consistent with the literature. We estimated the number of children who needed to be vaccinated to prevent 1 influenza-attributable hospitalization or 1 outpatient visit for each age group.

As both vaccine efficacy and severity of the influenza season increased, the number of children who needed to be vaccinated to prevent 1 hospitalization or 1 outpatient visit decreased. The numbers of children who needed to be vaccinated to prevent 1 hospitalization in a year with 50% vaccine efficacy ranged from 1031 to 3050 for children 6 to 23 months of age and from 4255 to 6897 for children 24 to 59 months of age. For every 12 to 42 children 6 to 59 months of age vaccinated in a year with 50% vaccine efficacy, we estimated that 1 influenza-attributable outpatient visit would be prevented.

With 1 outpatient visit being prevented through vaccination of <50 children, influenza vaccination can reduce influenza-attributable medical visits in children significantly, even in years with modest vaccine efficacy.