• The time to first vaginal swab that is type III GBS culture positive, with all previous cultures negative for type III GBS, not just the immediately preceding culture. [ Time Frame: Bacterial cultures will be performed every 2 months up to 18 months post-vaccination. ] [ Designated as safety issue: No ]
  

• The density of type III GBS cultured from vaginal swabs at culture positive visits. [ Time Frame: Bacterial cultures will be performed every 2 months up to 18 months post-vaccination. ] [ Designated as safety issue: No ]
  
• Frequency of local and systemic symptoms attributable to vaccination. [ Time Frame: Safety surveillance during the 1st 7 days. ] [ Designated as safety issue: Yes ]
  
• Proportion of vaginal swabs that are type III GBS culture positive. [ Time Frame: Bacterial cultures will be performed every 2 months up to 18 months post-vaccination. ] [ Designated as safety issue: No ]
  
• Frequency of vaginal colonization with GBS serotypes Ia, Ib, II and V. [ Time Frame: Bacterial cultures will be performed every 2 months up to 18 months post-vaccination. ] [ Designated as safety issue: No ]
  
• Measurement of serum IgG antibody levels to type III GBS. [ Time Frame: At 1, 2, 4, 6, 8, 10, 12, 14, 16, and 18 months following vaccination. ] [ Designated as safety issue: No ]
  
• Measurement of post-vaccination antibody levels to type III GBS, stratified by pre-vaccination levels of native antibody. [ Time Frame: At 1, 2, 4, 6, 8, 10, 12, 14, 16, and 18 months following vaccination. ] [ Designated as safety issue: No ]
  
• Proportion of subjects whose vaginal cultures are type III GBS culture negative throughout the study. [ Time Frame: Bacterial cultures will be performed every 2 months up to 18 months post-vaccination. ] [ Designated as safety issue: No ]
  

Vaginal colonization is the single most important risk factor for transmission of group B Streptococcus (GBS) from mothers to neonates, resulting in neonatal sepsis and/or meningitis. The long-term goal of this study is to determine whether vaccine-induced serum antibody to type III GBS will be sufficient to prevent vaginal acquisition of type III GBS. This study is linked to DMID protocol 04-018. This study is a randomized, double-blinded, comparative clinical trial among young (18-40 years old), non-pregnant, sexually active women who are not currently colonized vaginally or rectally with type III GBS, it will be conducted to evaluate the efficacy of a GBS type III-TT vaccine for prevention of type III GBS vaginal acquisition. The observation period for each patient will be 18 months following vaccination. The specific objectives are: enroll 600 women (previously screened within last 14 days in a GBS Screening Protocol) identified as GBS type III negative, vaginally and rectally; vaccinate 600 women randomized to a 1:1 ratio with 50 micrograms of type III GBS polysaccharide conjugated to tetanus toxoid (GBS III-TT) or licensed vaccine containing Tetanus and Diphtheria Toxoids adsorbed for adult use (Td); measure reactogenicity by subject report in a 7-day symptom diary and by 1-2 day follow-up telephone call; evaluate women at 1, 2, 4, 6, 8, 10, 12, 14, 16 and 18 months for serum antibody response. Blood will be obtained at each of these clinic follow-up visits and serum will be used to compare type III GBS specific antibody levels at baseline and follow-up; assess vaginal and rectal acquisition by GBS at months 1, 2, 4, 6, 8, 10, 12, 14, 16 and 18 months using specimens obtained at the clinic visits; compare women receiving GBS III-TT vaccine to women receiving Td vaccine with respect to the time to first vaginal culture positive for type III GBS; assess the relationship between person-level covariates, including features of the decrease of type III GBS antibody levels over time, and the time to first vaginal culture positive for type III GBS; and assess the effect of vaginal colonization by H2O2-producing Lactobacillus, sexual activity, antibiotic usage, rectal colonization with GBS and demographic features as risk factors for acquisition of type III GBS, independent of serum antibody levels. The primary study endpoint will be the time to the first vaginal swab that is type III GBS culture positive, with all previous cultures negative for type III GBS, not just the immediately preceding culture. The secondary endpoints include: the proportion of vaginal swabs that are type III GBS culture positive; the proportion of subjects whose vaginal cultures are type III GBS culture negative throughout the study; the frequency of vaginal colonization with GBS serotypes Ia, Ib, II and V; the measurement of serum IgG antibody levels to type III GBS at 1, 2, 4, 6, 8, 10 12, 14, 16 and 18 months following vaccination; the measurement of post-vaccination antibody levels to type III GBS, stratified by pre-vaccination levels of native antibody; the frequency of local and systemic symptoms attributable to vaccination; and the density of type III GBS cultured from vaginal swabs at culture positive visits.

Inclusion Criteria:

• Participated in and completed the GBS Screening Protocol
• Non-pregnant women
• Aged 18-40 years at time of the screening protocol
• Currently sexually active at time of enrollment (sex with a male at least once in the last 4 months)
• Current use of effective birth control methods and stated intention to use the method for at least the next 30 days
• Provision of written informed consent
• Intention to stay in the geographical area for the next 18 months
• Access to telephone

Exclusion Criteria:

• GBS positive by culture (vaginal and/or rectal), or culture positive for streptococcal strains that cross-react with GBS typing sera (vaginal and/or rectal)
• Pregnancy (all women will receive a urine pregnancy prior to vaccination)
• Any condition which in the opinion of the investigator would pose a health risk to the subject or interfere with the evaluation of the vaccine.
• Serious underlying disease, which is known at the time of vaccination (including: immunodeficiency, active or chronic hepatitis, immunosuppressive conditions which require systemic steroid therapy, or treatment for a malignancy during the past year).
• Receipt of any vaccine, blood product, or experimental medicine within the past 30 days with the exception of a licensed inactivated influenza vaccine.
• Plans to receive any vaccine, blood product, or experimental medicine in the next 30 days with the exception of a licensed inactivated influenza vaccine.
• Use of any antimicrobial agent (s) (vaginal or systemic) for treatment of any condition within 7 days prior to study enrollment.
• History of hypersensitivity to tetanus toxoid vaccine.
• Tetanus toxoid immunization within the previous 12 months.
• Previous participation in a study in which participants received tetanus toxoid vaccine or vaccine against Group B Streptococcus.
• Spontaneous or surgical menopause.
• Nursing mother.
• Hypersensitivity to thimerosal.