Haemophilus influenzae type b (Hib) conjugate vaccine generates T-cell-dependent immunity compared to plain polysaccharide vaccine. The key modification enabling this is:

• A Covalent linkage of the polysaccharide to a carrier protein (e.g., tetanus toxoid or CRM197) ✓
• B Addition of adjuvant alum to the polysaccharide antigen
• C Reduction of polysaccharide molecular weight by acid hydrolysis
• D Inclusion of a recombinant capsular protein alongside polysaccharide

Explanation

Plain polysaccharide antigens are T-independent antigens that stimulate B cells directly, producing short-lived IgM responses with no immunological memory and poor efficacy in children under 2 years. Conjugation to a carrier protein converts them to T-dependent antigens, enabling CD4+ T-cell help, class switching to IgG, affinity maturation, and long-lived memory B cell formation. Alum adjuvant enhances immune response but does not itself confer T-cell dependence. CRM197 is a non-toxic mutant diphtheria toxin used as a carrier in several conjugate vaccines.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.