In our randomised, observer-blind, parallel-group, controlled trial, healthy adults aged 18–44 years, 45–64 years, and 65 years and older (from Oct 19, to Nov 12, 2009) received two doses of vaccine given 21 days apart: either 7·5 μg of haemagglutinin formulated as whole-virion vaccine, or 3·75 μg of haemagglutinin formulated as split-virion vaccine with AS03A oil-in-water adjuvant. Assignment was by a computer-generated code, with random permuted blocks of two, four, and six. All participants and investigators were unaware of vaccine assignments. The trial was done at three hospitals in the UK. We measured antibody titres with a haemagglutination-inhibition assay at baseline; 7, 14, and 21 days after each vaccination; and at 6 months after the first dose. Primary outcome was vaccine immunogenicity of the full analysis set by the EU Committee of Human Medicinal Products licensing criteria. This study is registered with
At day 0, baseline antibody (titre ≥1/8) was detected in 44 (13 % ) of 347 participants. Sera from 95 % to 98 % of participants were assessed for immunogenicity on days 7, 14, 21, 28, 35, and 42, and at 6 months. On day 21 after one dose of adjuvanted AS03A or whole-virion vaccine, 63 (94 % , 95 CI 85·4–98·4) of 67 and 50 (71 % , 59·4–81·6) of 70 participants aged 18–44 years, 51 (77 % , 65·3–86·7) of 66 and 26 (39 % , 27·1–51·5) of 67 aged 45–64 years, and 19 (51 % , 34·4–68·1) of 37 and 11 (32 % , 17·4–50·5) of 34 aged 65 years or older had titres of 1:40 or greater. On day 42 (21 days after the second dose), 64 (100 % , 94·4–100) of 64 and 49 (73 % , 60·9–83·2) of 67 participants aged 18–44 years, 59 (91 % , 81·0–96·5) of 65 and 29 (43·9 % , 31·7–56·7) of 66 aged 45–64 years, and 28 (76 % , 58·8–88·2) of 37 and 12 (36 % , 20·4–54·9) of 33 aged 65 years or older had titres of 1/40 or greater. At 6 months, 62 (98 % , 91·5–100) of 63 and 54 (78 % , 66·7–87·3) of 69 participants aged 18–44 years, 54 (82 % , 70·4–90·2) of 66 and 37 (55 % , 42·6–67·4) of 67 aged 45–64 years, and 21 (57 % , 39·5–72·9) of 37 and 10 (29 % , 15·1–47·5) of 34 aged 65 years or older had titres of 1/40 or greater. There were no vaccine-related serious adverse events. Whole-virion vaccine was associated with fewer local and systemic reactions than adjuvanted vaccine.
AS03A-adjuvanted vaccine was more immunogenic against pandemic influenza A H1N1 virus than whole-virion vaccine and offers greater antigen-sparing capacity. A two-dose strategy should be considered for older people.
Department of Health, National Institute for Health Research Evaluation, Trials and Studies Coordinating Centre.