Administration of AS03B-adjuvanted A(H1N1)pdm09 vaccine in children under 3 years enhances antibody response to H3 and B viruses following a single dose of trivalent vaccine one year later

Background: We report a follow up clinical and serological investigation of 274 children receiving seasonal influenza vaccine (TIV) one year after receipt of either AS03B-adjuvanted subunit or whole virus monovalent A(H1N1)pdm09 vaccine and describe the antibody responses to the H3N2 A/Perth/16/2009 and B/Brisbane/60/2008 components of TIV.Method and Findings: Vaccine responses were analysed using Haemagglutination Inhibition (HAI) assays. In individuals under 3 years of age, previous receipt of adjuvanted vaccine resulted in higher HAI antibody responses to H3N2 and B strains compared to non-adjuvanted vaccine (fold change 16.8 vs 4.3 for H3N2 and 7.0 vs 1.6 for B). In older children, responses to the H3 and B components of TIV were similar between vaccine groups. Sera taken pre- and post pandemic vaccine were also analysed by HAI with A/Perth/16/2009 virus. This analysis showed that 11.1% of children receiving the AS03B-adjuvanted vaccine but only 1.4% in the non-adjuvanted group had a 4-fold rise to A/Perth/16/2009.Conclusion: AS03B-adjuvanted A(H1N1)pdm09 influenza vaccine generates a cross-reactive antibody response to H3N2 in children and enhances responses to heterologous subtypes in <3-year-old children one year later