The group B streptococcus (GBS) vaccine study is being done to see if a single vaccination with a GBS type III vaccine can stop women from getting GBS type III bacteria in the vagina. Approximately 600 women, ages 18-40, will be enrolled from the clinical sites participating in this study. Participants will be non-pregnant, sexually active (sex with a male at least once in the last 4 months), and GBS negative in the vagina or rectum at the screening visit. Participants will be randomly assigned to receive the experimental GBS type III vaccine or a licensed vaccine containing Tetanus and Diphtheria Toxoids (Td). Participants will be followed at one month, 2 months and every other month thereafter following vaccination (for vaginal and rectal swab collection and a blood draw) for 1½ years or a total of 10 post vaccination visits.