Background/ hypothesis

Natural history studies have correlated group B streptococcus (GBS) serotype-specific anti-capsular polysaccharide (CPS) IgG in newborns with reduced risk of GBS disease in early life. Hexavalent CPS glycoconjugate vaccine (GBS6) is being developed as a maternal vaccine to prevent invasive GBS in young infants.
Methods

C1091002 is an ongoing phase 2, placebo-controlled, study in pregnant women, assessing the safety and immunogenicity of a single dose of various GBS6 formulations with analysis of maternally transferred anti-CPS antibodies. Data is presented from participants in South Africa. A parallel seroepidemiology study in the same population assessed anti CPS IgG concentrations in infant sera associated with risk of invasive disease. A similar seroepidemiology study was undertaken in Finland.

Results
In both studies, naturally acquired anti-CPS IgG concentrations correlates well with reduced risk of disease. GBS6 induces a robust maternal antibody response to all six vaccine serotypes, with a measurable transplacental transfer of anti-CPS IgG. Natural immunity anti-CPS IgG levels, associated with a >80% risk reduction of invasive GBS disease, were used to predict the efficacy of maternally transferred (GBS6-induced) antibody levels.

Conclusion
This first evaluation of the GBS6 vaccine in pregnant women demonstrates that it induces antibodies transferred to infants at levels associated with a significant reduced risk of infant invasive GBS disease, based on natural immunity studies.