Madhi SA, Izu A, Kwatra G, et al. - Researchers intended to determine if there is an association between naturally-derived Group B streptococcus (GBS) serotype-Ia and III IgG and risk reduction of invasive GBS disease (IGbsD) in infants’ ≤ 90 days of age. IGbsD cases were identified from a cohort of 38,233 mother-newborn dyads in a matched case-control study. Cord-blood IgG concentration ≥ 1.04 and ≥ 1.53µg/ml were linked to a 90% risk reduction of serotype-Ia and III IGbsD, respectively. The threshold associated with a decreased risk for serotype-Ia and III IGbsD reported for infant sera supports the case for licensure of GBS polysaccharide-protein conjugate vaccine on the basis of an immunogenicity assessment benchmarked against the defined thresholds.