Key Inclusion Criteria:  Male or female subject 6 to 16 years of age on Day 1. Subject must provide informed consent (assent, depending on age) prior to participation in study and comply with protocol requirements. If female, the subject is not pregnant or lactating. If female of childbearing potential, the subject must agree to either be heterosexually inactive or follow birth control methods per protocol from at least 21 days prior to enrollment and through 90 days following any study vaccination. Subject has a stable health status, as established by physical examination, vital sign measurements, and medical history. Subject (and/or legal guardian) has access to a consistent and reliable means of electronic or telephone contact, which may be in the home, workplace, school, or by personal mobile electronic device. Subject is willing to refrain from routine nasal sprays (including steroid sprays) or washes for at least 7 days following any study vaccination.  Key Exclusion Criteria:  History of any component of Tdap vaccination or documented pertussis infection within 3 years prior to Day 1. Chronic significant illness actively being treated or a history of recent intervention for worsening or fluctuating symptoms (at the discretion of the investigator). History of cancer (malignancy). Congenital, hereditary, or acquired disease or disorder classified as autoimmune, immunodeficient, coagulopathy, hepatic, renal, neurologic, or cognitive. Currently uses smoking products (including vaping and e-cigarettes) and is unwilling to refrain from use from Day 1 through Day 29 following study vaccination. Subject received immunoglobulin, blood-derived products, systemic corticosteroids (at a dose of >10 mg per day for more than 10 days), or other immunosuppressant drugs within 90 days of Day 1. Chronic pulmonary disease requiring active medication or pulmonary therapies except exercise-induced bronchospasm, if currently well controlled, and willing to refrain from intense exercise for 7 days following study vaccination, or intermittent asthma classification who have not had an exacerbation requiring oral systemic corticosteroids in the past year; have an forced expiratory volume (FEV1) documented to be >80%; do not have restrictions in normal activity due to breathing issues; and have used a short-acting beta-agonist less than or equal to 2 days per week over the past 2 months. History of oro/nasopharynx surgery (eg, adenoidectomy, tonsillectomy) within 60 days prior to Day 1. Known hypersensitivity to latex or any component of any study vaccine. Specific to Boostrix: hypersensitivity to neomycin or polymyxin; hypersensitivity after previous administration of diphtheria, tetanus, or pertussis vaccines; or has experienced transient thrombocytopenia or neurological complications following an earlier immunization against diphtheria and/or tetanus. Subject has routine and/or repeated contact with, or is currently living in a household with, an immunocompromised individual. Subject resides in a residence where an infant less than 6 months of age resides or may reside.