The correct answer is A, "One dose of Tdap vaccine," as this is the recommended immunization for a 55-year-old nurse who received all childhood vaccinations. According to the Certification Board of Infection Control and Epidemiology (CBIC) guidelines, which align with recommendations from the Centers for Disease Control and Prevention (CDC) and the Advisory Committee on Immunization Practices (ACIP), adults who have completed a primary series of childhood vaccinations (typically 5 doses of DTaP or DTP) should receive a single booster dose of Tdap if they have not previously received it. This is especially critical for healthcare personnel, such as a 55-year-old nurse, due to their increased risk of exposure to pertussis and the need to protectvulnerable patients (CBIC Practice Analysis, 2022, Domain III: Infection Prevention and Control, Competency 3.2 - Implement measures to prevent transmission of infectious agents). The Tdap vaccine, which protects against tetanus, diphtheria, and pertussis, is recommended once between ages 11-64, with a preference for administration in early adulthood (e.g., 19-26 years) or as soon as feasible for older adults, including this 55-year-old nurse, to ensure immunity against pertussis, which wanes over time. For individuals aged 65 and older, Tdap is still recommended if not previously received, though Tdap is preferred over Td (tetanus and diphtheria only) for healthcare workers to address pertussis risk.

Option B (two doses of Tdap vaccine at least 14 days apart) and Option C (two doses of Tdap vaccine at least 28 days apart) are not standard recommendations for adults with a complete childhood vaccination history. Multiple doses are typically reserved for individuals with incomplete primary series or specific high-risk conditions, not for this scenario. Option D (no additional vaccination is recommended) is incorrect because, even with a complete childhood series, a Tdap booster is advised for healthcare workers to maintain protection, especially given the nurse’s occupational exposure risks (CDC Immunization Schedules, 2024). After receiving the Tdap booster, a Td booster every 10 years is recommended to maintain tetanus and diphtheria immunity, but the initial Tdap dose is the priority for this nurse.

The recommendation for one Tdap dose aligns with CBIC’s emphasis on evidence-based immunization policies to prevent transmission of vaccine-preventable diseases in healthcare settings (CBIC Practice Analysis, 2022, Domain III: Infection Prevention and Control, Competency 3.1 - Collaborate with organizational leaders). This ensures the nurse is protected and contributes to herd immunity, reducing the risk of pertussis outbreaks in the healthcare environment.