A randomised, double-blind, placebo-controlled phase I clinical trial to evaluate the safety, tolerability and immunogenicity of three doses of an adjuvanted group B Streptococcus vaccine in older adults aged 55 to 75.

Group B Streptococcus (GBS) disease is an increasing medical burden in adults. The present phase 1 trial evaluated an adjuvanted GBS vaccine (GBS-AlpN) containing N-terminal domains of four alpha-like proteins (AlpNs) (Alp1N, Alp2/3 N, RibN and AlpCN) in 60 healthy adults and 30 with obesity and/or type 2 diabetes (O/D) aged 55 to 75 years of age. Participants received three intramuscular doses of GBS-AlpN or placebo (48:12 and 24:6) on Day 1, Week 4 and Week 24. Solicited local and systemic adverse events (AEs), unsolicited AEs, and serious AEs (SAEs) were collected. Geometric mean concentrations of antibodies to the four AlpN antigens, and seroconversion were determined. The median age was between 65 and 66 years with more females in the healthy groups and more males in the O/D groups. Mainly mild solicited local and systemic AEs were reported for 53 healthy and 26 O/D participants. Seven SAEs, all unrelated, were reported (three in the placebo group and four in the active groups). At least 1 unsolicited AE was reported by 43 healthy and 22 O/D participants. None of the severe unsolicited AEs were related. By Day 57 all participants except three, who received GBS-AlpN had seroconverted for all four AlpNs. The vaccine elicited robust and durable antibody responses, already after the second dose, with comparable results between subgroups. These findings support further clinical investigation for the optimal vaccination strategy to protect vulnerable older adults against GBS disease.