Identification of Antigen and Adjuvant Doses Resulting in Optimal Immunogenicity and Antibody Persistence up to 1 Year After Immunization With a Pandemic A/H1N1 Influenza Vaccine in Children 3 to <9 Years of Age

Background: In the development of pediatric A/H1N1 influenza vaccines, this study was performed to identify antigen and adjuvant doses providing optimal immunogenicity and antibody persistence to ensure long-term immunity after immunization with an adjuvanted A/H1N1 vaccine in children 3 to <9 years of age. Methods: Healthy children (N = 1357) were immunized with 1 of 8 investigational vaccine formulations ranging in antigen (3.75-30 mu g) and MF59 adjuvant (Novartis Vaccines, Marburg, Germany; 0, 50 and 100% of standard dose). Each participant received 2 vaccine doses given 3 weeks apart. Immunogenicity was analyzed by hemagglutination inhibition assay in sera drawn 3, 4 and 6 weeks after first vaccination. Long-term antibody persistence was assessed 6 and 12 months after immunization. Vaccine safety was monitored throughout the study. Results: All MF59-adjuvanted vaccines were well tolerated and highly immunogenic, with adjuvanted formulations inducing antibody titers statistically superior to those of the nonadjuvanted vaccines. Each MF59-adjuvanted vaccine met all the US and European licensure criteria for influenza vaccines 3 weeks after the administration of a single dose; all nonadjuvanted formulations failed to meet licensure criteria at this time point. Antibody titers in response to a single vaccination with 7.5 mu g antigen and a full dose of MF59 continued to meet all US and European licensure criteria up to 1 year after immunization. Conclusion: A single dose of vaccine containing 7.5 mu g A/California/7/2009 (H1N1) antigen and a full dose of MF59 adjuvant was found to be optimal for children 3 to <9 years of age.