A Phase 2b Trial Evaluating the Safety, Tolerability, and Immunogenicity of a 6-Valent Group B Streptococcus Vaccine Administered Concomitantly With Tetanus, Diphtheria, and Acellular Pertussis Vaccine in Healthy Nonpregnant Female Individuals

Background Maternal group B streptococcus (GBS) infection is associated with substantial risk of preterm birth and infant mortality. Preventative approaches to protect infants from GBS infection are needed. Methods In this phase 2b, randomized study, healthy nonpregnant 18−49-year-old females were randomized 1:1:1 to receive the investigational 6-valent GBS polysaccharide conjugate vaccine (GBS6) and concomitant Tdap (GBS6+Tdap), GBS6 and placebo (GBS6+placebo), or Tdap and placebo (Tdap+placebo). Primary safety endpoints included reactogenicity events within 7 days and adverse events (AEs) through 1 month after vaccination. Primary immunogenicity objectives were to describe immune responses induced by GBS6+Tdap versus Tdap+placebo and versus GBS6+placebo for pertussis, tetanus, and diphtheria Tdap antigens and the 6 GBS6 antigens. Results Overall, 304 participants received study vaccination. Most reactogenicity events were mild or moderate in severity and balanced across vaccine groups. Frequency of AEs was ≤8.1% across vaccine groups. One-month after vaccination, the proportion of participants achieving antibody concentrations ≥0.1 IU/mL, for tetanus and diphtheria antigens was 100% in both GBS6+Tdap and Tdap+placebo groups. Immune responses to pertussis antigens were lower in the GBS6+Tdap group compared to the Tdap+placebo group, with geometric mean ratios <0.6. No consistent effect on immune responses against each of the GBS6 serotypes after concomitant administration with Tdap was observed. Conclusions GBS6 and Tdap administered concomitantly and alone were safe and well tolerated in healthy nonpregnant individuals. Similar immune responses were observed for Tdap when administered with GBS6 or when administered alone. These results will likely inform future studies in pregnant individuals. (NCT04766086).