Safety, efficacy, and effectiveness of live, attenuated, cold-adapted influenza vaccine in an indicated population aged 5-49 years

Background. Three important studies have supported licensure of live, attenuated, cold- adapted influenza vaccine ( CAIV- T [ FluMist; MedImmune Vaccines]): ( 1) a pediatric efficacy trial involving children 15 - 71 months of age, ( 2) a large safety study of medically attended events occurring among children 1 - 17 years of age, and ( 3) an effectiveness trial involving healthy working adults 18 - 64 years of age. Methods. During the United States Food and Drug Administration ( FDA) review for the approval of CAIV-T for use in healthy persons, additional subgroup analyses were conducted to evaluate the safety, efficacy, and effectiveness of the vaccine, by use of various age subsets not prespecified by the original protocols. CAIV- T is currently approved by the FDA for use in healthy persons 5 - 49 years of age. In this article, we present data from some of the aforementioned subanalyses. Results. The efficacy of CAIV- T in children greater than or equal to 5 years of age ( age range of the children in year 1 of the study, 60 - 71 months; age range of the children in year 2 of the study, 60 - 83 months) was similar to that reported for the entire cohort in year 1 ( 90.6%; 95% confidence interval [ CI], 70.3% - 97.1%). In year 2 of the study, efficacy was 86.9% ( 95% CI, 70.8% - 94.1%), despite the presence of antigenically drifted influenza type A/ Sydney/ 5/ 97 ( H3N2), which caused most illnesses that occurred in year 2. Safety outcomes for children 5 - 17 years of age revealed no significant difference between vaccine recipients and placebo recipients, with regard to acute respiratory events, acute gastrointestinal events, systemic bacterial infection, or rare events possibly related to influenza. Effectiveness among adults 18 - 49 years of age was similar to that reported for the entire cohort - for example, for occurrence of severe febrile illness, there was a 19.5% reduction (P = .02) in adults. Conclusions. The present reanalysis summarizes data on the indicated uses for CAIV- T in the indicated population aged 5 - 49 years.