Typhoid Ty21a vaccine differs fundamentally from the Vi capsular polysaccharide vaccine. Which set of properties correctly describes Ty21a?
- A Live attenuated oral vaccine given as enteric-coated capsules on alternate days ✓
- B Killed whole-cell oral vaccine given as three daily doses
- C Conjugate subunit vaccine given parenterally as a single dose after 2 years of age
- D Live attenuated parenteral vaccine requiring a booster every 3 years
Correct answer: A. Live attenuated oral vaccine given as enteric-coated capsules on alternate days
Explanation
Ty21a is the live attenuated Salmonella Typhi Ty21a mutant, supplied as enteric-coated capsules taken orally on alternate days for three or four doses, inducing both mucosal and systemic immunity. The older killed whole-cell oral and parenteral typhoid vaccines were withdrawn for reactogenicity. The Vi polysaccharide is an unconjugated injectable T-cell independent antigen needing boosters roughly every 3 years, and the Vi-conjugate (Typbar TCV) is a separate single-dose product, matching neither description.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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