Phase IIIb, Observer-blind Study to Compare Immunogenicity of GSK Biologicals' HPV-16/18 L1/AS04 Vaccine Versus Gardasil® [Quadrivalent Human Papillomavirus (HPV-6,11,16,18 L1 VLP) Recombinant Vaccine Merck & Co., Inc.]

HPV infection has been established as a necessary cause of cervical cancer. GSK Biologicals has developed an HPV-16/18 L1 VLP AS04 vaccine (Cervarix TM) which targets the 2 most common oncogenic HPV types (HPV-16 and HPV-18), found in > 70%, approximately, of all cervical cancers. Recently, Merck's HPV vaccine Gardasil® [quadrivalent human papillomavirus (HPV-6,11,16,18 L1 VLP) recombinant vaccine] has been approved by the FDA for prevention of genital tract cancers and pre-cancers and genital warts in females. Although the GSK HPV vaccine and Gardasil® have different compositions and are expected to have different efficacy profiles, each vaccine targets prevention of HPV-16 and 18 genital tract cancers and pre-cancers. Therefore, a comparison of the immunogenicity of the two vaccines is warranted. This Phase 3b study is designed to compare the immunogenicity of the GSK vaccine (HPV-16/18) to Gardasil® in healthy adult females 18-45 years of age. The Protocol Posting has been updated as the study will be extended by 3 additional years.