The aim of this study is to describe immunogenicity of a single booster dose of Adacel vaccine versus Boostrix vaccine among approximately 420 adolescents 11 to <13 years of age.

Primary objective:

• To describe seroprotection rates against tetanus and diphtheria in subjects randomized to receive either Adacel or Boostrix vaccine.

Observational objectives:

• To describe pre- and post-vaccination tetanus, diphtheria, and pertussis geometric mean antibody concentrations (GMCs) in subjects randomized to receive either Adacel or Boostrix vaccine.
• To describe booster response rates against tetanus, diphtheria, and pertussis in subjects randomized to receive either Adacel or Boostrix vaccine.
• To describe the rates of adverse events (AEs) immediately post-vaccination, and the rates of unsolicited AEs and serious adverse events (SAEs) following vaccination with Adacel or Boostrix vaccine from Visit 1 through Visit 2.

Participants will be randomized in a 1:1 ratio to receive either Adacel or Boostrix vaccine.

Subjects will be monitored for immediate reactions for 15 minutes post-vaccination. Unsolicited adverse events and serious adverse events will be collected from Visit 1 through Visit 2.

Inclusion Criteria:

• Subject is 11 to < 13 years of age at the time of vaccination
• Received exactly 5 doses of pertussis vaccine at < 7 years of age
• Informed consent and assent forms have been signed and dated
• Subject is able to attend all scheduled visits and to comply with all trial procedures.

Exclusion Criteria:

• Subject is pregnant, or lactating, or of child bearing potential without using an effective method of contraception or not practicing abstinence for at least 4 weeks prior to vaccination and until at least 4 weeks after vaccination
• Any condition that, in the opinion of the Investigator, would pose a health risk to the participant or interfere with the evaluation of the vaccine
• Chronic illness that, in the opinion of the Investigator, is at a stage where it might interfere with trial conduct or completion
• Known or suspected congenital or acquired immunodeficiency; or receipt of immunosuppressive therapy such as anti-cancer chemotherapy or radiation therapy within the preceding 6 months; or long-term systemic corticosteroid therapy (prednisone or equivalent for more than 2 consecutive weeks) within the past 3 months)
• Known or suspected receipt of any whole-cell pertussis-containing vaccine
• A personal history of physician-diagnosed or laboratory-confirmed pertussis disease within the last 2 years
• A previous severe reaction to pertussis, diphtheria or tetanus vaccine including immediate anaphylaxis, encephalopathy within 7 days, or seizure within 3 days of receiving the vaccine
• Receipt of immune globulins, blood or blood-derived products in the past 3 months
• Suspected or known hypersensitivity to any of the vaccine components, or history of a life-threatening reaction to the vaccine used in the trial or to a vaccine containing any of the same substances
• Receipt of any vaccine within 30 days before receiving study vaccine, or plans to receive another vaccine before the 2nd visit; except that influenza vaccine may have been received between 30 and 15 days (but no less than 15 days) before receiving study vaccine
• Participation in another interventional clinical trial investigating a vaccine, drug, medical device, or medical procedure in the 30 days preceding the first study vaccination or during the course of the study, at the discretion of the Sponsor
• Seropositivity for Human Immunodeficiency Virus (HIV), Hepatitis B, or Hepatitis C, as reported by the subject's parent/guardian
• Laboratory-confirmed thrombocytopenia, which may be a contraindication for intramuscular (IM) vaccination, at the discretion of the Investigator
• Bleeding disorder or receipt of anticoagulants in the 3 weeks preceding inclusion, which may be a contraindication for IM vaccination, at the discretion of the Investigator
• Personal history of Guillain-Barré syndrome
• Moderate or severe acute illness/infection (according to Investigator judgment) or febrile illness (temperature ≥ 38.0°C [≥ 100.4°F]) on the day of vaccination. (A prospective subject should not be enrolled in the study until the condition has resolved or the febrile event has subsided.)
• Identified as an Investigator or employee of the Investigator or study center with direct involvement in the proposed study, or identified as an immediate family member (i.e., parent, spouse, natural or adopted child) of the Investigator or employee with direct involvement in the proposed study
• Deprived of freedom by an administrative or court order, or in an emergency setting, or hospitalized involuntarily
• Current alcohol or drug use that, in the opinion of the Investigator, might interfere with the ability to comply with trial procedures.