Haemophilus influenzae type b capsular polysaccharide (PRP) (Hib PRP)

Haemophilus influenzae type b (Hib) capsular polysaccharide, specifically polyribosylribitol phosphate (PRP), is the primary immunogenic component used in vaccines to prevent invasive Hib disease. In its conjugate form, PRP is chemically linked to a carrier protein—such as tetanus toxoid or a non-toxic diphtheria toxin mutant (CRM197)—to transform the polysaccharide from a T-cell independent to a T-cell dependent antigen (WHO: Hib Position Paper). This modification is essential for efficacy in infants and young children, whose immune systems are otherwise unable to mount a robust or lasting response to pure polysaccharides. Upon administration, the conjugate antigen triggers the production of specific IgG antibodies that promote the opsonization and complement-mediated destruction of Hib bacteria, effectively preventing life-threatening conditions like meningitis and pneumonia (PubMed: 1275838). The antigen serves a strictly prophylactic role, priming the host immune system to recognize and neutralize the pathogen upon future exposure. Since the global implementation of PRP-conjugate vaccines, the incidence of invasive Hib infections has declined by more than 90% in many populations (CDC: Pink Book).

Other names

Polyribosylribitol phosphatePRPHaemophilus influenzae type b conjugate antigenHaemophilus b polysaccharideHib antigen

The conjugate antigen induces active immunity by stimulating a T-cell dependent immune response. By covalently linking the Hib capsular polysaccharide (PRP) to a carrier protein, the immune system is able to recruit T-helper cells, which facilitates the production of high-affinity IgG antibodies and the establishment of long-term immunological memory, particularly in infants (StatPearls: NBK539824).