Immunogenicity and safety of a novel AS03A-adjuvanted H1N1 2009 pandemic influenza vaccine in adults in Japan

Background and objectives: This study evaluated the immunogenicity and safety of a novel H1N1 2009 pandemic vaccine (A/California/7/2009) in Japanese adults. Results: Following Dose 1, seroprotection rate (HI titre >= 1:40) was 95%, seroconversion rate was 94% and the geometric mean titre (GMT) was 230.3 (geometric mean fold rise [GMFR]: 26.3). Following Dose 2, seroprotection rate as well as seroconversion rate were 100%; HI antibody GMT rose to 485 (GMFR: 55.4). European and United States regulatory acceptance criteria for immunogenicity were met and exceeded following each dose of the vaccine. Solicited symptoms recorded during the 7-day post-vaccination follow-up period were of mild to moderate intensity (Grade 3: <= 4% of subjects). The most frequently reported solicited symptoms after both doses were pain at the injection site, fatigue and muscle ache. Unsolicited adverse events causally related to vaccination were reported in 18 subjects; none were of Grade 3 intensity. There were no serious adverse events. Methods: This open-label, single-group, multi-center Phase II study enrolled 100 healthy subjects aged 20-64 years (stratification [1: 1] by age: 20-40 years and 41-64 years) to receive 21 days apart, two doses of a monovalent, split-virion AS03(A)-adjuvanted H1N1 2009 pandemic vaccine (3.75 mu g hemagglutinin [HA]). Blood samples collected before vaccination and 21 days after each dose were analyzed using hemagglutination inhibition (HI) assay. Conclusion: A single dose of AS03(A)-adjuvanted, 3.75 mu g HA H1N1 2009 pandemic influenza vaccine was highly immunogenic in Japanese adults with a clinically acceptable safety profile, thereby making it a potential candidate for mitigating A/H1N1-associated morbidity and mortality.