The present application relates to immunogenic compositions comprising staphylococcal PNAG which is less than 40% N-acetylated and is conjugated to a carrier protein by a linker bonded to an amine group on PNAG to form a PNAG conjugate. Vaccines, methods of treatment using and processes to make an immunogenic composition comprising PNAG and Type 5 and/or 8 capsular polysaccharides are also described.