A polysaccharide derivative that is the capsular polysaccharide of Harmophilus influenzae type b, consisting of (5->3)-phosphodiester-linked beta-Dribofuranosyl-(1->1)-D-ribitol units. The whole can be conjugated to a carrier protein [e.g. CRM197, outer membrane protein complex (OMPC)] at a single site on the polysaccharide reducing end or randomly along the polysaccharide chain (cross-linked). An example structure is shown in the diagram.