A modified polysaccharide, in particular a modified Neisseria meningitidesserogroup A polysaccharide, which retains immunogenicity but has improvedstability. Typically, the modified polysaccharide is prepared by reacting acapsular polysaccharide, or oligosaccharide fragment thereof, with abifunctional reagent such as CDI, followed by reaction with an amino compound,such dimethylamine. Modified polysaccharide-protein conjugates and vaccinesprepared from such conjugates are also described.
