Study participants will include 150 boys and girls aged 4-8 years (total, 75 boys and 75 girls) to receive 2 doses of the 9vHPV vaccine at 0 and 12 months. Patients will be recruited by age-group to achieve balanced enrollment of 15 girls and 15 boys per year of age. The investigators will examine the immunogenicity profile in this cohort, for which titers will be analyzed one month after dose 2 (Month 13) and at Month 60.~Though clinical efficacy cannot be assessed in young children because of limited exposure to human papillomavirus (HPV), this descriptive study will allow the investigators to understand whether the 9vHPV vaccine in younger patients provides immunogenicity similar to that shown for the 9-14 and 16-26 age groups who have received the 9vHPV vaccine.13 This study will require an IND for the use of the HPV vaccine in children younger than 9 years.~Immunogenicity will be measured by examining serum antibodies of all participants using a competitive Luminex immunoassay (cLIA).15 Month 60 serology will be by cLIA and IgG LIA assays. The antibody response testing will be performed at Merck Research Laboratory.~The goal of this study is to explore whether a 2-dose 9vHPV vaccine regimen with dosage separated by 12 months is immunogenic among children aged 4-8 years. The primary outcome will be geometric mean titers (GMT) for HPV6, HPV11, HPV16, HPV18, HPV31, HPV33, HPV45, HPV52, and HPV58 antibodies at months 13 and 60. Results will allow the investigators to qualitatively compare immunogenicity in individuals vaccinated at age 4-8 years to known immunogenicity in 9vHPV recipients vaccinated at ages 9-14.13 Knowledge of whether vaccination in this age group is sufficient to induce high-level protective antibody titers through 4 years after the second dose will support further efficacy studies in a larger randomized trial of a 2-dose 9vHPV regimen for children aged 4-8 years.
This study is an open-label nonrandomized exploratory proof of concept and descriptive 4-year immunogenicity study to assess immunogenicity after administration of a 2-dose regimen of 9-valent human papillomavirus vaccine (9vHPV) vaccine separated by 12 months (months 0, 12).