Efficacy of inactivated and cold-adapted vaccines against influenza A infection, 1985 to 1990: the pediatric experience

Background. Influenza is a common and potentially serious infection in children. Although there is interest in broadening the use of influenza vaccine in healthy children, there are few large, randomized, controlled trials that evaluate the safety and efficacy of inactivated vaccine in the pediatric population. Methods. From 1985 through 1990 a randomized, controlled trial of cold-adapted and inactivated vaccines for the prevention of influenza A disease was conducted at Vanderbilt University, and the cumulative results from this trial in patients of all ages have been previously published. We reanalyzed the data from this trial in the subset of patients who were younger than 16 years at the time of their participation. We determined vaccine safety, immunogenicity and efficacy, based on culture-positive illness and seroconversion, in this subset of patients. Results. During the 5 years of the study, 791 children younger than 16 years received 1809 doses of either inactivated or cold-adapted vaccine or placebo. The vaccines were well-tolerated, and there were no serious reactions. Inactivated trivalent influenza vaccines were 91.4 and 77.3% efficacious in preventing symptomatic, culture-positive influenza A H1N1 and H3N2 illness, respectively. The efficacy of the inactivated vaccine based on hemagglutination inhibition assay seroconversion was 67.1 and 65.5%, respectively, for H1N1 and H3N2 serotypes. Conclusions. Inactivated trivalent influenza A vaccines are well-tolerated and efficacious in the prevention of influenza A disease in children 1 to 16 years old.