THE PRESENT APPLICATION RELATES TO IMMUNOGENIC COMPOSITIONS COMPRISING TYPE 5 AND/OR 8 CAPULAR POLYSACCHARIDE OR OLIGOSACCHARIDE FROM S. AUREUS HAVING BETWEEN 30-100% O-ACETYLATION. VACCINES, METHODS OF TREATMENT USING AND PROCESSES TO MAKE AN IMMUNOGENIC COMPOSITION COMPRISING TYPE 5 AND/OR 8 CAPSULAR POLYSACCHARIDES WITH 30-100% O-ACETYLATION ARE ALSO DESCRIBED.