The invention provides a process for preparing a conjugate of a S. aureus type 5 or type 8 capsular polysaccharide and a carrier molecule, comprising the steps of: (a) depolymerizing the capsular polysaccharide, to give a polysaccharide fragment (b) oxidizing the fragment in order to introduce an aldehyde group into at least one saccharide residue in the fragment, to give an oxidized saccharide residue and (c) coupling the oxidized 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.
