A randomized trial of conjugated group B streptococcal type Ia vaccine in a rabbit model of ascending infection

OBJECTIVE: Maternal vaccination may become a central strategy in the preven tion of early-onset group B Streptococcal sepsis. Unlike earlier group B st reptococcal polysaccharide vaccines that were poorly immunogenic, newer vac cines conjugated to tetanus toroid have been developed and have improved im munogenicity. We sought to evaluate a conjugated vaccine using our rabbit m odel of ascending infection. STUDY DESIGN: Rabbit does were randomized to receive either conjugated grou p B streptococcal type Ia (Ia-tetanus toroid) or conjugated group B strepto coccal type III (III-tetanus toroid) vaccine. Does were vaccinated 7 days b efore conception and 7 and 21 days after conception. On days 28 to 30 of a 30-day gestation, does were inoculated intracervically with 10(6) colony-fo rming units of type Ia group B Streptococcus. Labor was induced ii does wer e undelivered after 72 hours. Does were observed up to 7 days after inocula tion. Offspring were observed up to 4 days. We obtained maternal cultures f rom the uterus, peritoneum, and blood and offspring cultures from the mouth , anus, and blood. Antibody levels were also determined. RESULTS: Offspring survival was significantly improved in the group receivi ng Ia-tetanus toroid (P = .047). Outcomes such as maternal sepsis and sever e illness, although not reaching statistical significance, showed a trend t oward improved outcomes in the Ia-tetanus toroid group. CONCLUSIONS: This is the first study to evaluate the conjugated group B str eptococcal vaccine by using any model of ascending infection. The Ia-tetanu s toroid vaccine led to improved survival and was immunogenic but fell shor t of its expected efficacy in preventing ascending group B streptococcal di sease under these experimental conditions.