A 30-year-old man presents with a deep, contaminated laceration and unknown tetanus vaccination history. He receives both tetanus toxoid and tetaneous immunoglobulin (TIG) at the same visit, injected at separate sites. The rationale for administering both simultaneously is that:

• A TIG neutralizes the tetanus toxoid to prevent anaphylaxis, while the toxoid primes future immunity
• B TIG provides immediate passive neutralization of circulating toxin, while the toxoid induces active antibody formation without interference between the two ✓
• C The toxoid blocks tissue-binding sites for tetanospasmin, allowing TIG to be cleared more slowly from circulation
• D TIG enhances the antigen-presenting cell uptake of toxoid, converting a T-independent response into a T-dependent one

Explanation

Tetanus toxoid induces active immunity by stimulating the patient's own B cells to produce antibodies, a process that takes days to weeks. TIG provides immediate passive neutralization of free toxin. They are given at separate anatomical sites to avoid direct antigen-antibody neutralization at the injection site, but the toxoid still elicits an active response. Option A is wrong because TIG does not neutralize toxoid systemically to block immunization. Option C misstates the mechanism entirely. Option D incorrectly assigns an immunologic enhancement role to passive immunoglobulin.

Reference: Plotkin's Vaccines, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.