Long-term immunogenicity of an AS03-adjuvanted influenza A(H1N1)pdm09 vaccine in young and elderly adults: An observer-blind, randomized trial()

BACKGROUND: This study (NCT00979602) evaluated the immunogenicity and relative protective efficacy of one dose of influenza A(H1N1)pdm09 vaccine with or without AS03 (an α-tocopherol oil-in-water emulsion based Adjuvant System). METHODS: Four thousands and forty-eight healthy adults aged ≥18 years were randomized (1:1) to receive one dose of either the adjuvanted split virion (3.75 μg hemagglutinin antigen [HA]/AS03) or non-adjuvanted (15 μg HA) vaccine. Hemagglutination inhibition [HI] antibody response was evaluated before vaccination and at Days 21, 42 and 182 (Month 6). Safety of the study vaccines was evaluated during the entire study duration. RESULTS: At Day 21, both study vaccines induced HI immune responses meeting the US regulatory criteria in subjects 18–64 years (seroprotection rate [SPR]: 98.0% [97.1–98.6]; seroconversion rate [SCR]: 89.7% [88.0–91.2] in the AS03-adjuvanted group; SPR: 91.4% [89.9–92.8]; SCR: 74.6% [72.3–76.9] in the non-adjuvanted group) and >64 years of age (SPR: 86.0% [82.5–89.0]; SCR: 75.3% [71.1–79.2] in the AS03-adjuvanted group; SPR: 69.1% [64.6–73.3]; SCR: 56.7% [52.0–61.3] in the non-adjuvanted group). The AS03-adjuvanted vaccine induced higher HI geometric mean titers than the non-adjuvanted vaccine at all time points. At Month 6, only subjects 18–64 years of age from both vaccine groups still met the US regulatory criteria (SPR: 82.1% [80.0–84.1]; SCR: 62.3% [59.6–64.8] in the AS03-adjuvanted group; SPR: 75.3% [72.9–77.5]; SCR: 53.7% [51.0–56.4] in the non-adjuvanted group). Protective efficacy was not evaluated due to low number of RT-qPCR-confirmed A(H1N1)pdm09 influenza cases. Through Month 12, 216 serious adverse events (in 157 subjects: 84 in the AS03-adjuvanted and 73 in the non-adjuvanted group) and 12 potentially immune mediated diseases (5 in the AS03-adjuvanted and 7 in the non-adjuvanted group) were reported. CONCLUSION: A single dose of either adjuvanted or non-adjuvanted influenza A(H1N1)pdm09 vaccine induced protective HI antibody levels against the A/California/7/2009 strain that persisted through Month 6 in the 18–64 years population.