HPV infection has been established as a necessary cause of cervical cancer. GSK Biologicals has developed an HPV-16/18 L1 VLP AS04 vaccine 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 in order to comply with the FDA Amendment Act, Sep 2007.

Inclusion Criteria:

• A woman whom the investigator believes that she or her legally acceptable representative (in the event that the subject is illiterate) can and will comply with the requirements of the protocol (e.g., completion of the diary cards, return for follow-up visits).
• A woman between and including 18 and 45 years of age at the time of the first vaccination.
• Written informed consent must be obtained from the subject prior to enrollment.
• Subject must be free of obvious health problems as established by medical history and history-directed clinical examination before entering into the study.
• Subject must have a negative urine pregnancy test.
• Subject must be of non-childbearing potential, or if she is of child bearing potential, she must practice adequate contraception for 30 days prior to vaccination, have a negative pregnancy test and continue such precautions for 2 months after completion of the vaccination series.
• Subject must have an intact cervix.

Exclusion Criteria:

• Use of any investigational or non-registered product (drug or vaccine) other than the study vaccine(s) within 30 days preceding the first dose of study vaccine, or planned use during the study period up to Month 24.
• Chronic administration (defined as more than 14 days) of immunosuppressants or other immune-modifying drugs within six months prior to the first vaccine dose or planned administration during the study period up to Month 24.
• Planned administration/administration of a vaccine not foreseen by the study protocol within 30 days before and 30 days after (i.e. days 0-29) each dose of vaccine. Administration of routine vaccines up to 8 days before each dose of study vaccine is allowed. Enrolment will be deferred until the subject is outside of specified window.
• Pregnant or breastfeeding. Women must be at least 3 months post-pregnancy and not breastfeeding to enter the study.
• A woman planning to become pregnant or planning to discontinue contraceptive precautions during approximately the first eight months of the study (Months 0-8).
• Previous administration of components of the investigational vaccine
• Previous or planned vaccination against HPV outside of this protocol.
• Any medically diagnosed or suspected immunodeficient condition based on medical history and physical examination.
• History of allergic disease, suspected allergy or reactions likely to be exacerbated by any component of the study vaccines.
• Hypersensitivity to latex.
• Known acute or chronic, clinically significant pulmonary, cardiovascular, neurologic, hepatic or renal functional abnormality, as determined by previous physical examination or laboratory tests.
• History of significant medical conditions and currently under treatment.
• Received immunoglobulins and/or blood product within 90 days preceding enrolment or planned administration during the study period up to Month 24. Enrollment will be deferred until the subject is outside of specified window.
• Acute disease at the time of enrolment. Enrollment will be deferred until condition is resolved. All vaccines can be administered to persons with a minor illness
• Heavy bleeding (menstruation or other) or heavy vaginal discharge in which a pelvic exam cannot be performed. Enrollment will be deferred until condition is resolved according to investigator's medical judgement.