The invention provides a process for preparing a conjugate of a S.aurens type 5 or type 8 capsular polysaccharide and a carrier molecule, comprising the steps of: (a) depolymerising the capsular polysaccharide, to give a polysaccharide fragment (b) oxidising the fragment in order to introduce an aldehyde group into at least one saccharide residue in the fragment, to give an oxidised saccharide residue and (c) coupling the oxidised saccharide residue to a carrier molecule via the aldehyde group, thereby giving the conjugate. The coupling in step (c) may be direct, or may be via a linker molecule. The invention also provides a conjugate obtained or obtainable by this process.
