The present invention relates to a lipopolysaccharide moiety comprising a conserved triheptosyl inner-core moiety of lipopolysaccharide substantially free of variable outer core oligosaccharide chain extension, and to vaccines obtaines therefrom which are cross-reactive for Haemophilus influenzae strains. The invention also relates to defined mutations in the biosynthetic machinery for lipopolysaccharide (LPS;) expression in Haemophilus influenzae useful to obtain the abovementioned moiety. The invention also relates to using conjugates of the LPS from the mutant strains so obtained to elicit a heterologous immune response against a wide range of disease-causing H. influenzae strains. More specifically, the invention relates to vaccines for prevention of bacterial infections comprising core lipopolysaccharide of Haemophilus influenzae.