Which component of the current Indian immunisation schedule protects against Haemophilus influenzae type b disease, and what property of the vaccine accounts for its efficacy in infants?

• A Live attenuated bacterial vaccine inducing cellular immunity
• B Plain purified polyribosylribitol phosphate polysaccharide inducing T-independent response
• C Capsular PRP conjugated to a carrier protein inducing T-dependent response and memory ✓
• D Outer membrane protein vesicles without any polysaccharide component

Explanation

Hib vaccines consist of the capsular PRP polysaccharide covalently conjugated to a carrier protein such as tetanus toxoid. Conjugation converts the T-independent polysaccharide response into a T-dependent response, producing class switching, affinity maturation, and memory effective in infants under 18 months. The plain unconjugated PRP vaccine failed in infants, which is the fact that eliminates option B.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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