A polysaccharide derivative that is the group C polysaccharide of Neisseria meningitidis, consisting of alpha(2->9)-linked sialic acid units. The polysaccharide chains can be conjugated to a carrier protein (e.g. CRM197), tetanus toxoid, ovalbumin, Hel) at a single site on the polysaccharide reducing end, at both termini of the (difuntional) polysaccharide chain or randomly along the polysaccharide chain (cross-linked).