Safety and immunogenicity of a single booster dose of the group B streptococcus AlpN candidate vaccine (GBS-AlpN) in previously vaccinated healthy women compared with a single dose in previously unvaccinated women.

Group B streptococcus (GBS; Streptococcus agalactiae) infection during pregnancy is an important cause of adverse pregnancy outcomes and life-threatening neonatal infections. All GBS strains have surface proteins that belong to the alpha-like protein (Alp) family. Following the demonstration of the safety and immunogenicity of a maternal GBS vaccine containing the fused N-terminal domains of two Alp proteins (αCN and RibN) in healthy adult women, a second-generation vaccine has been developed (GBS-AlpN, GBS-NN/NN2), which also contains the N-terminal domain of the Alp1 and Alp2/3 proteins (Alp1N and Alp2/3 N). We assessed the safety and immunogenicity of a single dose of GBS-AlpN in previously vaccinated and unvaccinated, healthy, non-pregnant women. The previously vaccinated women had received two doses of GBS-AlpN, a mean of 2.5 years previously. A single dose of GBS-AlpN was well-tolerated and elicited a strong booster antibody response against all four Alp-N-terminal domains in previously vaccinated women and a weaker primary response in the previously unvaccinated women. If these results can be generalised to pregnant women, it is likely that two doses will be required for an initial pregnancy, but a single dose could be sufficient in subsequent pregnancies in clinical practice.