The adult Tdap vaccine (Boostrix) contains a reduced dose of diphtheria toxoid compared to the pediatric DTaP vaccine. The immunological rationale for reducing the diphtheria toxoid dose in adults is:
- A Lower dose reduces reactogenicity while memory cells still mount a protective response ✓
- B Adults lack memory B cells for diphtheria toxoid
- C Adults have naturally acquired immunity from environmental exposure
- D Diphtheria toxoid is degraded more rapidly in adult muscle tissue
Correct answer: A. Lower dose reduces reactogenicity while memory cells still mount a protective response
Explanation
Adults primed by childhood vaccination have memory A cells that rapidly respond to even a reduced antigen dose. The full pediatric dose in adults increases local and systemic reactogenicity (fever, arthralgia) without proportional benefit. Hence Tdap uses lower-case 'd' (reduced diphtheria toxoid) and lower-case 'p' (reduced pertussis antigens) compared to DTaP.
Reference: Plotkin's Vaccines, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.