The disclosure describes compositions containing PEGylated compounds using linkers, bivalent polysaccharide covalent PEG compounds, and methods of bivalent polysaccharide-PEG compounds in the development of multivalent vaccines. PEGylated conjugation of capsular polysaccharides to carrier proteins is carried out using homo-bifunctional and/or hetero-bifunctional linkers of specific lengths. Incorporation of bifunctional PEG linkers induces higher titers of functional antibodies with high avidity, eliciting higher immunologic memory, and reduced carrier protein effect. This provides immunochemically cross-reactive capsular polysaccharides wherein one or more cross-reactive capsular polysaccharides are covalently PEG compounded sequentially or concurrently to carrier protein using bifunctional linkers bearing the same or different functional groups. Such a linker and the size of the capsular polysaccharides provides an effective multivalent vaccine with high antibody titers and a reduced carrier effect, with a reduction in the content of the capsular polysaccharide and protein per dose of vaccine which reduces reactogenicity.
