A method for making a multivalent immunogenic conjugate, comprising: (a) reacting a plurality of polysaccharides from encapsulated bacteria, with an oxidizing agent resulting in a mixture of a plurality of aldehyde-activated polysaccharides, wherein the plurality of polysaccharides are from distinct bacteria or distinct serotypes; reacting a carrier protein with hydrazine, carbohydrazide, hydrazine chloride, a dihydrazide or a mixture thereof under conditions sufficient to produce a solution of a hydrazide-activated carrier protein; contacting the mixture of the plurality of aldehyde-activated polysaccharides with the hydrazide-activated carrier protein at a pH of 5 to 8 such that the plurality of aldehyde-activated polysaccharides simultaneously react with the hydrazide-activated carrier protein resulting in a multivalent conjugate that includes at least one C=N double bond formed between each conjugated polysaccharide and the carrier protein; and reducing substantially all of the C=N double bonds of the multivalent conjugate to C-N bonds resulting in a multivalent immunogenic conjugate product, or (b) reacting a plurality of polysaccharides from encapsulated bacteria with a cyanylation agent resulting in a mixture of a plurality of cyanate-activated polysaccharides, wherein the plurality of polysaccharides are from distinct bacteria or distinct serotypes; reacting a carrier protein with hydrazine, carbohydrazide, hydrazine dichloride, a dihydrazide, or a mixture thereof under conditions sufficient to produce a solution of a hydrazide-activated carrier protein; and contacting the mixture of the plurality of cyanate-activated polysaccharides with the hydrazide-activated carrier protein at a pH of 6 to 8 such that the plurality of cyanate-activated polysaccharides simultaneously react with the hydrazide-activated carrier protein resulting in a multivalent immunogenic conjugate that includes at least one C-N bond formed between each conjugated polysaccharide and the carrier protein. (a) reacting a plurality of polysaccharides from encapsulated bacteria, with an oxidizing agent resulting in a mixture of a plurality of aldehyde-activated polysaccharides, wherein the plurality of polysaccharides are from distinct bacteria or distinct serotypes; reacting a carrier protein with hydrazine, carbohydrazide, hydrazine chloride, a dihydrazide or a mixture thereof under conditions sufficient to produce a solution of a hydrazide-activated carrier protein; contacting the mixture of the plurality of aldehyde-activated polysaccharides with the hydrazide-activated carrier protein at a pH of 5 to 8 such that the plurality of aldehyde-activated polysaccharides simultaneously react with the hydrazide-activated carrier protein resulting in a multivalent conjugate that includes at least one C=N double bond formed between each conjugated polysaccharide and the carrier protein; and reducing substantially all of the C=N double bonds of the multivalent conjugate to C-N bonds resulting in a multivalent immunogenic conjugate product, or (b) reacting a plurality of polysaccharides from encapsulated bacteria with a cyanylation agent resulting in a mixture of a plurality of cyanate-activated polysaccharides, wherein the plurality of polysaccharides are from distinct bacteria or distinct serotypes; reacting a carrier protein with hydrazine, carbohydrazide, hydrazine dichloride, a dihydrazide, or a mixture thereof under conditions sufficient to produce a solution of a hydrazide-activated carrier protein; and contacting the mixture of the plurality of cyanate-activated polysaccharides with the hydrazide-activated carrier protein at a pH of 6 to 8 such that the plurality of cyanate-activated polysaccharides simultaneously react with the hydrazide-activated carrier protein resulting in a multivalent immunogenic conjugate that includes at least one C-N bond formed between each conjugated polysaccharide and the carrier protein.