This is a single-center, prospective, open-label, partially randomized, matched-controlled trial designed as a cohort study. The study plans to enroll 360 healthy female participants aged 18 to 45 years, divided into three groups: a three-dose sequential group, a two-dose sequential group, and a primary immunization group, with 120 participants in each group. All participants will be stratified by two age subgroups (18-26 years and 27-45 years) to ensure demographic balance across groups.
As blinding is not feasible in this study, a prospective, open-label, partially randomized, controlled trial design is adopted. A combination of randomized and non-randomized (i.e., partially randomized) enrollment methods is used to balance study feasibility with intergroup comparability.
Participants in the three-dose sequential group and the primary immunization group will receive one dose of the nine-valent HPV vaccine at months 0, 1, and 6, while those in the two-dose sequential group will receive the nine-valent HPV vaccine at months 0 and 6. Before the second and third doses, investigators must confirm that participants do not meet the criteria for early withdrawal or for postponement of the second and third doses. After each vaccination, a 30-minute safety observation will be conducted at the vaccination site to monitor for adverse events (AEs). Subsequently, the study visit procedures will be followed, including collection of solicited AEs within 7 days post-vaccination, unsolicited AEs within 30 days, and serious AEs (SAEs) throughout the study period. Participants will also complete other scheduled study visits, including safety observations and immunogenicity blood sampling at various time points before and after vaccination.
The study aims to evaluate the immune response characteristics and safety of sequential vaccination with different doses of the nine-valent HPV vaccine (three doses at 0, 1, 6 months and two doses at 0, 6 months) in healthy female participants who have previously completed vaccination with the bivalent HPV vaccine.