The vaccine for Haemophilus influenzae type b targets which serotype?

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

Answer: (B)

Haemophilus influenzae disease in children is mainly caused by encapsulated strains, with type b being the most virulent and historically responsible for invasive infections like meningitis. The Hib vaccine targets the type b capsule by using a conjugate of the capsular polysaccharide (polyribosylribitol phosphate) attached to a protein carrier, which boosts the immune response in infants and creates lasting protection. Because the vaccine is specific to the type b capsule, it effectively prevents infections caused by serotype b, while non‑typeable strains (lacking a capsule) or other serotypes with different capsules are not covered by this vaccine. So the vaccine targets serotype b.