SAFETY AND IMMUNOGENICITY OF A TETRAVALENT GROUP-B STREPTOCOCCAL POLYSACCHARIDE VACCINE IN HEALTHY-ADULTS

Proposed strategies for prevention of neonatal group B streptococcal ( GBS) infection have included active immunization of pregnant women and passive immunization of high-risk infants with hyperimmune GBS globul in derived from vaccinated plasma donors. To explore the feasibility o f a program for generating hyperimmune GBS globulin, we evaluated the safety and immunogenicity of a candidate multivalent GBS vaccine conta ining purified polysaccharide from types Ia, Ib, II, and III among sub jects most likely to develop an immune response following vaccination, ie. those with pre-existing antibody to GBS. Thirty volunteers prescr eened for serum antibody to type III GBS were immunized with a single subcutaneous injection of vaccine containing either 10, 25, or 50 mu g of each polysaccharide type (Group 1). An additional ten volunteers p rescreened for antibody to the Ia were vaccinated with the 50 mu g dos e (Group 2). Vaccination was generally well tolerated with minor react ions occurring in 27% of subjects. Using a quantitative enzyme-linked immunosorbent assay (ELISA), the seroconversion rates (greater than or equal to four-fold rise) and geometric mean antibody concentration (G MC in mu g IgG ml(-1)) 6 weeks after vaccination in Group I to type Ia , II, and III were 33% (GMC 5.2), 17% (GMC 3.6), and 70% (GMC 43.4), r espectively. Quantitative titers were not available or type Ib, but a fourfold rise in ELISA units was seen in 13% of subjects. In Group 2, seroconversion rates to type Ia and III were 90% (GMC 73.4) and 40% (G MC 22.2), respectively. No significant dose-response effect was detect ed Combined analysis of Groups I and 2 demonstrated that subjects with prevaccination antibody concentrations >2 mu g IgG ml(-1) had signifi cantly higher type-specific antibody concentrations following vaccinat ion compared with subjects possessing lower levels of antibody before immunization, We conclude that our tetravalent GBS polysaccharide vacc ine is safe but only modestly immunogenic in healthy seropositive adul ts. More potent vaccines will be required for public health use. Copyr ight (C) 1996 Elsevier Science Ltd.