Long-Term Immune Persistence After Bivalent HPV Vaccination in Females From Study 311-HPV-1005

Inclusion criteria

• Previously enrolled in Study 311-HPV-1005 (NCT04965350) at the Mianyang Center for Disease Control and Prevention.
• Received at least one dose of the bivalent HPV vaccine in the base study.
• For the immunogenicity persistence subset: completed all three doses in the base study and had valid neutralizing antibody results before vaccination and one month after the third dose.
• For the breakthrough-case cohort: at least 18 years of age at extension-study enrollment or becoming 18 years of age during the extension study.
• Participant provided written informed consent; for a participant younger than 18 years at extension-study enrollment, the participant and at least one parent or legal guardian provided written informed consent or assent as required.
• Able to understand and comply with the study procedures. Participants in the immunogenicity persistence subset agreed to blood collection at Months 42 and 66. Participants in the breakthrough-case cohort agreed to scheduled remote or site follow-up and to provide relevant HPV- and cervical-disease information.

Exclusion criteria

• Receipt of any other HPV vaccine during Study 311-HPV-1005 or between completion of the base study and enrollment in this extension.
• At a visit involving blood collection, any condition that may interfere with venipuncture, including a platelet count below 20 x 10^9/L, phlebitis, or hemophilia.
• Any other factor that, in the investigator's judgment, makes the participant unsuitable for the study.