To access the immune persistence of Chinese women aged 9-45 years after receiving quadrivalent HPV vaccine with the immunization schedule of 0, 2 and 6 months.

Inclusion Criteria:

• Subjects who participated in the phase III clinical trial of non inferior efficacy of HPV tetravalent vaccine of Yangchun Center for Disease Control and Prevention (protocol No.: 4-HPV-3001), completed three doses of HPV quadrivalent vaccine and provided blood sample at months 7; Or subjects who have participated in the bridging study of HPV quadrivalent vaccine of Mianyang Center for Disease Control and Prevention (scheme No.: 4-HPV-3002), completed the whole vaccine schedule at month 0，2，6, and provided blood sample at months 7;
• The subjects aged 9 to 17 years old at Mianyang site and their legal guardian should provide legal indentification; the subjects aged over 18 years old should provide legal indentification;
• The subject voluntarily agrees to enroll in this study. If the subject is a minor, both the subject and subject's legal guardian should voluntarily agree to enroll in this study and sign an informed consent form;
• Be able to understand the study procedures and promise to participate in regular follow-ups under the requirements.

Exclusion Criteria:

• Enrolling or plan to enroll in other clinical trials (drugs or vaccines) (except that the observational clinical study and the subjects at Mianyang site are still in the post exemption safety follow-up stage of the 4-HPV-3002 trial);
• Suffering from thrombocytopenia or any coagulation dysfunction that can be a contraindication to blood collection (such as coagulation factor deficiency, coagulation diseases, platelet abnormalities, etc.);
• According to the investigator's judgment, the subject has any condition may interfere with process of evaluation of immune persistence.

Subjects aged 9-45 years old have completed receiving three doses of quadrivalent HPV vaccine and provided blood sample at month 7