Pfizer Research Devlopment Brooklyn, NY, United States
Introduction: Natural history studies correlated serotype-specific anti–capsular polysaccharide (anti-CPS) IgG in newborns with reduced risk of GBS disease. Group B streptococcus 6-valent polysaccharide conjugate vaccine (GBS6) is being developed to prevent invasive GBS disease in infants through maternal immunization. Methods: An ongoing Phase 1/2, placebo-controlled study in South Africa assessed safety and immunogenicity of a single dose of different GBS6 formulations. Sera before and at set timepoints after maternal vaccination and cord blood or infant sera taken at delivery were assessed for anti-CPS IgG. Maternal participants recorded reactogenicity events 7 days after vaccination and unsolicited safety events through 12 months after delivery, including pregnancy-specific outcomes. Infant unsolicited safety events through 12 months of age, including birth outcomes, were recorded. Results: 360 Maternal participants were enrolled. GBS6 induced robust maternal antibody response to all six vaccine serotypes. Infants born to GBS6-vaccinated mothers had higher anti-CPS IgG geometric mean concentrations at birth compared to placebo, with the highest among 20 µg GBS6 recipients.
Proportions of adverse and serious adverse events were similar among all groups. Pregnancy and birth outcomes, including preterm births, were similar among all groups. One stillbirth occurred in a GBS6 recipient and was considered by the investigator unrelated to the vaccine. Conclusion/Implications: GBS6 was safe and well-tolerated. Infant IgG levels at birth were at levels associated with a significant reduced risk of invasive GBS disease, based on natural history studies. Based on an optimal immunogenicity profile, 20 µg GBS6 without AlPO4 was chosen to continue into Stage 3 and future licensure studies.
