Safety and Long-term Humoral Immune Response in Adults After Vaccination With an H1N1 2009 Pandemic Influenza Vaccine With or Without AS03 Adjuvant

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Abstract
(See the editorial commentary by Neuzil, on pages 700–1 .) Background. In this study (NCT00985088) we evaluated different formulations of an H1N1 2009 pandemic influenza vaccine that deliver various viral hemagglutinin (HA) doses with or without AS03 (a tocopherol-based oil-in-water adjuvant system). Methods. A total of 1340 healthy subjects aged ≥18 years were randomized to receive 1 or 2 doses of an adjuvanted (3.75-μg HA/AS03A or 1.9-μg HA/AS03B) or nonadjuvanted vaccine formulation. Safety and immunogenicity (by hemagglutination-inhibition [HI] assay) after each dose and 6 months after dose 1 are reported here. Results. A single dose of AS03A-adjuvanted 3.75-μg HA H1N1 2009 induced the strongest immune responses in subjects aged 18−64 years (seroprotection rate [SPR], 97.2%; seroconversion rate [SCR], 90.1%) as well as in subjects aged >64 years (SPR, 91.1%; SCR, 78.2%) 21 days after vaccination. Six months after dose 1, subjects who received 2 doses of either the adjuvanted formulation or 1 dose of the adjuvanted 3.75-μg HA formulation continued to meet all Center for Biologics Evaluation and Research and Committee for Medicinal Products for Human Use criteria. All formulations had clinically acceptable safety profiles. Conclusion. A single dose of the 3.75-μg HA AS03A-adjuvanted H1N1 2009 influenza vaccine was highly immunogenic in both age strata (18−64 and >64 years), inducing long-term persistence of the immune response until at least 6 months after dose 1.