The role of nasal IgA in children vaccinated with live attenuated influenza vaccine

AbstractBackgroundImmunoglobulin A (IgA) is the predominant antibody produced in response to mucosal infections. The role of IgA in providing protection against influenza in children vaccinated with live attenuated influenza vaccine (LAIV) has not been well described.MethodsNasal IgA responses were assessed using data from 3 prospective, 2-year, randomized studies comparing LAIV with placebo in children 6–36 months of age. In each study, samples were collected in a subset of patients; a new cohort was enrolled each year. Ratios of strain-specific nasal IgA to total nasal IgA were calculated and prevaccination to postvaccination geometric mean fold-rises (GMFRs) were evaluated. Mean postvaccination IgA ratios were compared for subjects with and without confirmed influenza illness by study and in pooled analyses.ResultsAcross studies, a higher percentage of children receiving LAIV had a ≥2-fold increase in strain-specific IgA ratio compared with placebo recipients. GMFRs after LAIV in years 1 and 2 ranged from 1.2 to 6.2, compared with 0.5–2.2 among placebo recipients. Similar responses were observed in subjects who were baseline seronegative and seropositive based on serum hemagglutination inhibition antibody titers. In years 1 and 2, the mean postvaccination strain-specific to total IgA ratio was 3.1-fold (P<0.01) and 2.0-fold (P