A Rapid Immune Response to 2009 Influenza A(H1N1) Vaccines in Adults: A Randomized, Double-Blind, Controlled Trial

A double-blind, randomized, controlled trial involving 706 adults was conducted to evaluate the immunogenicity and safety of different dosages of whole-virion or split-virion H1N1 influenza vaccines with or without aluminum adjuvant. A rapid and strong immune response was induced at day 14 after the first injection. The seroprotection rates ranged from 72.7% (95% confidence interval [CI], 62.7%-81.1%) for 5-mu g whole-virion aluminum formulation to 97.0% (95% CI, 90.9%-99.7%) for 30-mu g split-virion nonaluminum formulation. All formulations were well tolerated. The incidences of mild, moderate, and severe reactions were 71 (10.1%), 15 (2.1%), and 1 (0.1%) of 706 reactions, respectively. The 15-mu g split-virion formulation had the best immunogenicity and safety.