Group B Streptococcus (GBS) is a Gram‑positive commensal bacterium that frequently colonizes the gastrointestinal and genital tracts. Maternal colonization is common in pregnancy and contributes to substantial neonatal morbidity and mortality worldwide. The source article cites estimates of approximately 20 million pregnant individuals colonized in 2020 and annual global burdens that include about 231,800 cases of early‑onset neonatal disease and 162,200 cases of late‑onset disease, together resulting in an estimated 91,900 infant deaths each year. Survivors of invasive neonatal GBS disease also face a measurable risk of moderate or severe neurodevelopmental impairment.
The investigational vaccine evaluated in this trial is a hexavalent capsular polysaccharide–protein conjugate, referred to as GBS6, formulated to provide coverage against the six capsular polysaccharide serotypes (Ia, Ib, II, III, IV and V) that collectively account for more than 97% of infant GBS disease globally. The vaccine aims to induce maternal serotype‑specific antibodies that can be transferred to the fetus to prevent early‑ and late‑onset neonatal disease.
This randomized phase 1/2 trial assessed safety, tolerability and immunogenicity of GBS6 in both non‑pregnant and pregnant participants and evaluated infant antibody responses. The trial comprised multiple stages:
The trial is registered on ClinicalTrials.gov under identifier NCT03765073.
In stage 1, 66 non‑pregnant participants were randomized with 22 participants in each group (GBS6, GBS6 + AlPO4, placebo). Twenty‑six participants subsequently received a GBS6 + AlPO4 booster.
In stage 3, 216 pregnant participants were included: 108 received GBS6 and 108 received placebo. From these maternal participants, 209 infants were born and followed: 104 infants whose parent received GBS6 and 105 infants whose parent received placebo.
Primary objectives focused on vaccine safety and tolerability. Across stages, nearly all reported reactogenicity events were classified as mild or moderate.
Among non‑pregnant participants in stage 1, no serious adverse events (SAEs) or adverse event–related withdrawals were reported after vaccination. Medically attended adverse events (MAEs) occurred at similar percentages across the primary vaccination groups (approximately 41–45% in the GBS6 groups and 41% in placebo).
In pregnant participants, overall rates of adverse events, SAEs and delivery outcomes were reported as similar between the GBS6 and placebo groups. The source reports AE frequencies for maternal participants (GBS6 = 75/108 (69%); placebo = 70/108 (65%)) and SAE counts (GBS6 = 21/108 (19%); placebo = 23/108 (21%)).
Most infant outcomes were also similar between groups. Infant AEs, SAEs and MAEs occurred at comparable frequencies for infants born to vaccinated versus placebo mothers: infant AE frequencies were 87/104 (84%) in the GBS6 group and 86/105 (82%) in the placebo group; infant SAEs were 45/104 (43%) and 46/105 (44%), respectively; infant MAEs were 65/104 (63%) and 66/105 (63%).
Two neonatal deaths associated with sepsis occurred during follow‑up, one in the GBS6 group and one in the placebo group; the report states that neither death was considered related to vaccination.
The trial report indicates that most infants were born full‑term. Frequencies of delivery outcomes were reported as similar between GBS6 and placebo maternal participants. Specific details about gestational age distributions, birth weight statistics or other neonatal clinical parameters beyond the aggregated AE/SAE/MAE frequencies and the two sepsis‑associated deaths are not provided in the source summary presented here.
Secondary objectives examined immune responses. The source reports that GBS6 elicited robust immune responses in both non‑pregnant and pregnant participants. Importantly, vaccinated pregnant participants generated serotype‑specific quantitative and functional antibodies, and corresponding serotype‑specific antibody responses were observed in infants born to vaccinated parents, indicating transplacental antibody transfer.
The source does not provide detailed numerical antibody titers, fold‑rise data or specific functional assay results in the summary presented here; those quantitative immunogenicity details are reported in the full article and associated supplementary materials referenced by the original publication.
In this randomized phase 1/2 trial, the hexavalent GBS6 vaccine demonstrated an acceptable safety and tolerability profile in non‑pregnant and pregnant participants, elicited robust serotype‑specific immune responses, and resulted in detectable serotype‑specific antibodies in infants of vaccinated parents. Adverse event rates and delivery outcomes were similar between vaccine and placebo groups, and the two neonatal sepsis‑associated deaths observed were not attributed to vaccination.
Based on these findings, the authors state that the data support continued clinical investigation of maternal GBS6 vaccination. The source indicates that some dose‑finding data from stage 2 were reported elsewhere and are not included in the presented summary. Further details and full immunogenicity metrics should be consulted in the full article and supplementary materials of the original publication.