Neisseria meningitidis vaccine

A method of producing a conjugate of a Neisseria meningitidis capsular polysaccharide to a carrier protein, comprising:

• a) partially de-O-acetylating the polysaccharide by alkaline hydrolysis to an O-acetylation level ranging from 0.6 μmol/mg polysaccharide to 1.5 μmol/mg polysaccharide;
• b) activating the polysaccharide by periodate treatment, thereby converting diols to aldehydes to an extent of at least 20 nmol aldehyde per mg polysaccharide;
• and
• c) conjugating the activated polysaccharide to the carrier protein by reductive amination, wherein the polysaccharide is present in the conjugation reaction at a weight-to-weight ratio of 1:1 to 5:1 relative to the carrier protein, thereby forming the conjugate;
• wherein the conjugate is a population comprising double-end-linked conjugated polysaccharides and single-end-linked conjugated polysaccharides which are both directly attached to the carrier protein through a secondary amine,
• wherein the polysaccharides of the conjugate to the carrier protein have an O-acetylation level ranging from 0.6 μmol/mg polysaccharide to 1.5 μmol/mg polysaccharide,
• wherein the polysaccharide is MenC capsular polysaccharide, and
• wherein the carrier protein is tetanus toxoid.