Methods for synthesis and manufacture of polysaccharide-protein conjugate vaccines at high yield are provided. The methods involve reaction of a hydrazide group on one reactant with an aldehyde or cyanate ester group on the other reactant. The reaction proceeds rapidly with a high conjugation efficiency, such that a simplified purification process can be employed to separate the conjugate product from the unconjugated protein and polysaccharide and other small molecule by-products.
