The Haemophilus influenzae vaccine protects against which serotype?

• A. Serotype a
• B. Serotype c
• C. Serotype b
• D. Serotype d

Answer: (C)

Haemophilus influenzae type b is the serotype most commonly linked to serious invasive illness in children, such as meningitis and epiglottitis. The Hib vaccine is a conjugate vaccine that uses the type b capsule polysaccharide (polyribosylribitol phosphate, PRP) linked to a protein carrier to provoke a strong, T‑cell–dependent immune response in infancy. This generates anti-PRP antibodies and immune memory that specifically protect against disease caused by the type b serotype. Other serotypes (a, c, d, etc.) aren’t targeted by this vaccine, and non‑typable strains lacking a capsule aren’t covered either. Thus, the vaccine protects against serotype b.