Safety and Immunogenicity of 2 Doses Versus 1 Dose of Acellular Pertussis Vaccines Containing Genetically-detoxified Pertussis Toxin in Young Adults Previously Primed With Acellular Pertussis Vaccines

Inclusion Criteria: * Has provided written informed consent; * Male or female, ages 18 to 30 years (inclusive) at the time of enrollment; * With documented history of acellular pertussis immunization (5 doses); * Free of clinically significant health problems, as determined by pertinent medical history and clinical examination at study screening; * Non-pregnant, non-lactating females : * Able to attend all scheduled visits during one year and to understand and comply with the study procedures; Exclusion Criteria: * Prior dTpa immunization within the last 5 years or prior dT immunization within the last 2 years, or any other investigational vaccine likely to impact on interpretation of the trial data * Suspected or confirmed pertussis infection within the last 10 years or documented pertussis infection in a household member within the last 10 years; * History of severe local or systemic reactions to any vaccination; * Known hypersensitivity or allergy to diphtheria, tetanus, or pertussis-containing vaccines (including excipients); * Receipt of investigational product up to 30 days prior to enrollment or ongoing participation in another interventional clinical trial; * Receipt of licensed vaccines within 30 days of planned study immunization or ongoing participation in another clinical interventional trial likely to interfere with study results; * Acute or chronic, clinically significant psychiatric, hematologic, pulmonary, cardiovascular, or hepatic or renal functional abnormality as determined by the Investigator based on medical history and physical exam; * Any confirmed or suspected immunosuppressive or immunodeficient condition, including human immunodeficiency virus (HIV) infection, asplenia, cytotoxic therapy in the previous 5 years, and/or diabetes; * Has a known history of vaccine-induced Guillain-Barré Syndrome; * Has an active malignancy or recent (\<10 years) history of metastatic or hematologic malignancy; * Suspected or known alcohol and/or illicit drug abuse within the past 5 years; * Pregnant or lactating female, or female intending to becoming pregnant during the study period; * Administration of immunoglobulins within the 120 days preceding study entry or planned administration during the study period; * History of blood donation (at least 450 ml) within 30 days of enrollment or plans to donate within the 30 days following and preceding each blood draw; * Receipt of chronic (\>14 days) immunosuppressants or other immune-modifying drugs within 6 months of study entry: * Any other significant finding that, in the opinion of the investigator, would increase the risk of the individual's having an adverse outcome by participating in this study.