What is a conjugate vaccine and give an example?

• A. A vaccine that uses attenuated viruses to trigger immunity.
• B. A vaccine that uses only inactivated toxins.
• C. A vaccine made from whole bacteria weakened in the lab.
• D. A vaccine that links a polysaccharide capsule to a protein to enhance immune response; Hib vaccine.

Answer: (D)

Conjugate vaccines pair a bacterial polysaccharide capsule with a protein carrier to boost the immune response. Polysaccharide antigens alone often provoke a weak, mostly short-lived response, especially in young children because they mainly stimulate a B-cell response without strong T-cell help. Attaching the polysaccharide to a protein provides T-helper cell involvement, leading to a better, longer-lasting antibody response with class switching to IgG and durable memory. An example is the Haemophilus influenzae type b (Hib) vaccine, where the Hib polysaccharide is linked to a protein such as a tetanus or diphtheria toxoid. This conjugation makes the vaccine effective in infants and has dramatically reduced Hib disease.