A Neisseria meningitidis vaccine composition comprising: a) a first conjugate of MenA capsular polysaccharide to a carrier protein; b) a second conjugate of MenC capsular polysaccharide to a carrier protein; c) a third conjugate of MenW-135 capsular polysaccharide to a carrier protein; and d) a fourth conjugate of MenY capsular polysaccharide to a carrier protein; wherein: (i) the second conjugate is a population comprising double-end-linked conjugated polysaccharides and single-end-linked conjugated polysaccharides, and the polysaccharides of the second conjugate have an O-acetylation level of 0.3 μmol/mg polysaccharide to 1.6 μmol/mg polysaccharide, and wherein the single-end-linked conjugated polysaccharides have a terminal unlinked saccharide; (ii) the MenA capsular polysaccharide is attached to the carrier protein through a linker comprising a carbamate, a spacer, and an amide, wherein the spacer is between the carbamate and the amide and comprises 2-10 linear carbons, and the first conjugate has a polysaccharide to carrier protein mass ratio of 0.3 to 1.5; (iii) the MenC, MenW-135, and MenY capsular polysaccharides are attached to the carrier protein through a secondary amine and at least one of the conjugates has a weight average molecular weight ranging from 300 kDa to 1500 kDa; (iv) the carrier protein is tetanus toxoid, and the composition comprises less than 20% free polysaccharide by weight relative to total polysaccharide. a) a first conjugate of MenA capsular polysaccharide to a carrier protein; b) a second conjugate of MenC capsular polysaccharide to a carrier protein; c) a third conjugate of MenW-135 capsular polysaccharide to a carrier protein; and d) a fourth conjugate of MenY capsular polysaccharide to a carrier protein; wherein: (i) the second conjugate is a population comprising double-end-linked conjugated polysaccharides and single-end-linked conjugated polysaccharides, and the polysaccharides of the second conjugate have an O-acetylation level of 0.3 μmol/mg polysaccharide to 1.6 μmol/mg polysaccharide, and wherein the single-end-linked conjugated polysaccharides have a terminal unlinked saccharide; (ii) the MenA capsular polysaccharide is attached to the carrier protein through a linker comprising a carbamate, a spacer, and an amide, wherein the spacer is between the carbamate and the amide and comprises 2-10 linear carbons, and the first conjugate has a polysaccharide to carrier protein mass ratio of 0.3 to 1.5; (iii) the MenC, MenW-135, and MenY capsular polysaccharides are attached to the carrier protein through a secondary amine and at least one of the conjugates has a weight average molecular weight ranging from 300 kDa to 1500 kDa; (iv) the carrier protein is tetanus toxoid, and the composition comprises less than 20% free polysaccharide by weight relative to total polysaccharide. (i) the second conjugate is a population comprising double-end-linked conjugated polysaccharides and single-end-linked conjugated polysaccharides, and the polysaccharides of the second conjugate have an O-acetylation level of 0.3 μmol/mg polysaccharide to 1.6 μmol/mg polysaccharide, and wherein the single-end-linked conjugated polysaccharides have a terminal unlinked saccharide; (ii) the MenA capsular polysaccharide is attached to the carrier protein through a linker comprising a carbamate, a spacer, and an amide, wherein the spacer is between the carbamate and the amide and comprises 2-10 linear carbons, and the first conjugate has a polysaccharide to carrier protein mass ratio of 0.3 to 1.5; (iii) the MenC, MenW-135, and MenY capsular polysaccharides are attached to the carrier protein through a secondary amine and at least one of the conjugates has a weight average molecular weight ranging from 300 kDa to 1500 kDa; (iv) the carrier protein is tetanus toxoid, and