The purpose of this study is to describe the safety and immunogenicity of repeat administration of Adacel vaccine approximately 10 years following initial administration of the vaccine. Antibody levels prior to revaccination will also be used to characterize antibody persistence following initial vaccination 10 years earlier.

Primary Objectives:

• To compare seroprotection rates against tetanus and diphtheria induced by Adacel vaccine to those induced by Td Adsorbed vaccine.
• To compare booster response rates against tetanus and diphtheria induced by Adacel vaccine to those induced by Td Adsorbed vaccine.
• To compare anti-pertussis geometric mean antibody concentrations (GMCs) induced by Adacel vaccine to the GMCs induced by Daptacel® vaccine given to infants.

Secondary Objectives:

• To describe the rates of immediate reactions, solicited reactions, unsolicited adverse events (AEs), and serious adverse events (SAEs) following vaccination with Adacel or Td Adsorbed vaccine.
• To describe booster response rates for pertussis antigens following revaccination with Adacel vaccine.

Healthy adults < 65 years of age who received Adacel vaccine 10 years previously will be randomized to receive either Adacel or TENIVAC (Td Adsorbed) vaccine. They will be assessed for immunogenicity at baseline and post-vaccination. Safety data will be collected for 6 months following vaccination.

Inclusion criteria:

• Subject is ≥ 18 to < 65 years of age at the time of vaccination.
• Received Adacel vaccine no less than 9 and no more than 11 years previously.
• Informed consent form has 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. Females who are pre-menarche or post-menopausal for at least one year, or surgically sterile will not be excluded.
• 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 tetanus toxoid (T), tetanus and diphtheria toxoids (Td), or tetanus and diphtheria toxoids and acellular pertussis (Tdap) vaccine since receipt of the qualifying dose of Adacel vaccine described in Inclusion Criterion #2.
• A personal history of physician-diagnosed or laboratory-confirmed pertussis disease within the last 10 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.
• Laboratory-confirmed thrombocytopenia, which may be a contraindication for 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 intramuscular (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.

Qualified researchers may request access to patient level data and related study documents including the clinical study report, study protocol with any amendments, blank case report form, statistical analysis plan, and dataset specifications. Patient level data will be anonymized and study documents will be redacted to protect the privacy of trial participants. Further details on Sanofi's data sharing criteria, eligible studies, and process for requesting access can be found at: https://vivli.org