An immunogenic composition comprising a purified group B streptococcal capsular polysaccharide, wherein the purified group B streptococcal polysaccharide is produced by a process comprising - providing for extraction isolated bacterial cells, concentrated bacterial supernatants from homogenized bacterial cells or conditioned medium, or pelleted cells comprising a group B streptococcal capsular polysaccharide; - extracting the capsular polysaccharide from cellular components, wherein the cellular components include nucleic acid and protein, by contacting the isolated bacterial cells, concentrated bacterial supernatants from homogenized bacterial cells or conditioned medium, or pelleted cells with a base reagent, selected from the bases NaOH, KOH, LiOH, NaH, NaOMe, or KO t Bu, wherein the bases are used in a range of 0.5 N to 5.0 N and whereby bacterial DNA and RNA are degraded; - separating by hydrophobic-interaction chromatography the extracted capsular polysaccharide from impurities resulting from the cellular components which comprise proteins and nucleic acids; and - recovering the purified capsular polysaccharide; wherein the group B streptococcal capsular polysaccharide is selected from the group consisting of type Ia CPS, type Ib CPS, type II CPS, type III CPS and type V CPS, and, wherein: type Ia CPS, after said separating step, has K av of the range 0.010 - 0.005 M w of the range 318 - 311 (kg/mol) M w /M n of the range 1.35 -1.31; type Ib CPS, after said separating step, has K av of the range 0.191 - 0.150 M w of the range 218 - 170 (kg/mol) M w /M n of the range 1.61 - 1.20; type II CPS, after said separating step, has K av of the range 0.152 - 0.115 M w of the range 289 - 246 (kg/mol) M w /M n of the range 1.46; type III CPS, after said separating step, has K av of the range 0.343 - 0.268 M w of the range 108 - 104 (kg/mol) M w /M n of the range 1.24 - 1.22; type V CPS, after said separating step, has K av of the range 0.257 - 0.156 M w of the range 179 - 92 (kg/mol) M w /M n of the range 1.28 - 1.15. - providing for extraction isolated bacterial cells, concentrated bacterial supernatants from homogenized bacterial cells or conditioned medium, or pelleted cells comprising a group B streptococcal capsular polysaccharide; - extracting the capsular polysaccharide from cellular components, wherein the cellular components include nucleic acid and protein, by contacting the isolated bacterial cells, concentrated bacterial supernatants from homogenized bacterial cells or conditioned medium, or pelleted cells with a base reagent, selected from the bases NaOH, KOH, LiOH, NaH, NaOMe, or KO t Bu, wherein the bases are used in a range of 0.5 N to 5.0 N and whereby bacterial DNA and RNA are degraded; - separating by hydrophobic-interaction chromatography the extracted capsular polysaccharide from impurities resulting from the cellular components which comprise proteins and nucleic acids; and - recovering the purified capsular polysaccharide; type Ia CPS, after said separating step, has K av of the range 0.010 - 0.005 M w of the range 318 - 311 (kg/mol) M w /M n of the range 1.35 -1.31; K av of the range 0.010 - 0.005 M w of the range 318 - 311 (kg/mol) M w /M n of the range 1.35 -1.31; type Ib CPS, after said separating step, has K av of the range 0.191 - 0.150 M w of the range 218 - 170 (kg/mol) M w /M n of the range 1.61 - 1.20; K av of the range 0.191 - 0.150 M w of the range 218 - 170 (kg/mol) M w /M n of the range 1.61 - 1.20; type II CPS, after said separating step, has K av of the range 0.152 - 0.115 M w of the range 289 - 246 (kg/mol) M w /M n of the range 1.46; K av of the range 0.152 - 0.115 M w of the range 289 - 246 (kg/mol) M w /M n of the range 1.46; type III CPS, after said separating step, has K av of the range 0.343 - 0.268 M w of the range 108 - 104 (kg/mol) M w /M n of the range 1.24 - 1.22; K av of the range 0.343 - 0.268 M w of the range 108 - 104 (kg/mol) M w /M n of the range 1.24 - 1.22; type V CPS, after said separating step, has K av of the range 0.257 - 0.156 M w of the range 179 - 92 (kg/mol) M w /M n of the range 1.28 - 1.15. K av of the range 0.257 - 0.156 M w of the range 179 - 92 (kg/mol) M w /M n of the range 1.28 - 1.15.