• Joanne M Langley, Louise Frenette, Robert Jeanfreau, Scott A Halperin, Michael Kyle, Laurence Chu, Shelly McNeil, Mamadou Dramé, Philippe Moris, Louis Fries, and David W Vaughn.
• Canadian Center for Vaccinology, 5850 University Avenue, Dalhousie University, IWK Health Centre and Capital Health District, Halifax, B3K 6R8 Canada. Electronic address: jmlangle@dal.ca.
• Vaccine. 2015 Jan 15;33(4):559-67.

BackgroundHighly pathogenic avian influenza A/H5N1 viruses continue to circulate in birds and infect humans causing serious illness and death.MethodsIn this randomized, observer-blinded study, adults ≥18 years of age (n=841) received 3.75 or 7.5 μg hemagglutinin antigen (HA) of an AS03-adjuvanted (AS03A or AS03B) A/Indonesia/5/2005 H5N1 (subclade 2.1) vaccine (priming), followed by the same HA dose of AS03-adjuvanted A/turkey/Turkey/1/05 H5N1 (clade 2.2) influenza vaccine as a booster 6 or 18 months after priming; an unprimed group received placebo at Day 0, and 3.75 μg HA of AS03A-adjuvanted booster vaccine at 6 and 18 months. Antibody responses were assessed by hemagglutination-inhibition assay (HI). Microneutralization (MN) antibody and cellular immunoassays were assessed in a subset of participants.ResultsGeometric mean titers (GMTs) and seroconversion rates (SCRs) were higher in primed vs. unprimed subjects against the booster strain 10 days following booster vaccination at month 6 and month 18. After the booster at 18 months, the lower limit of the 97.5% confidence interval for the difference in SCR and GMT ratios between primed and unprimed subjects was >15% and >2.0, respectively, fulfilling the primary endpoint criteria for superiority against the booster strain. MN and cellular immune responses corresponded with the immunogenicity seen in HI measures.ConclusionsAdults primed with a dose-sparing oil-in-water adjuvanted H5N1 subclade vaccine had rapid and durable antibody responses to a heterologous subclade boosting vaccine given 6 or 18 months later.Copyright © 2014 The Authors. Published by Elsevier Ltd.. All rights reserved.

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