Study design and objectives
This is a Phase IIa, single-arm, open label, non-randomized trial of a nonavalent prophylactic HPV vaccine among 9–11-year-old girls and boys to determine the stability and kinetics of antibody titers induced after a single dose over 24 months, with a deferred-booster dose at 24 months and optional booster at 30 months. Participants provide blood specimens at 6, 12, 18, 24, and 30 months after the first dose. Serologic geometric mean titers (GMT) of the nine vaccine types (HPV 16/18/ 6/11/31/33/45/52/58) will be measured at each collection time. The primary objective is to determine the stability of type-specific serologic GMT of HPV16 and HPV18 between the 6- vs. 12-month, 12- vs. 18-month, and 18- vs. 24-month visits. Secondary objectives are to determine the stability of type-specific serologic GMT of the other HPV types (HPV 6/11/31/33/45/52/58) between the visits and to assess safety and reactogenicity after each vaccine dose. The study hypothesis is that a single dose of the nonavalent HPV vaccine will induce persistent and stable serological responses for up to 24 months to all 9 vaccine HPV types. This study is being conducted among participants from the youngest of the licensed ages (9–11 years) such that very few, if any, of these participants will have become sexually active within the two year period before their deferred booster dose. In addition, younger age children are likely to mount higher immune titers [
11] and the immune responses to a single dose or two doses of the HPV vaccines among girls aged 9–14 years appear to be comparable to antibody responses of 3 doses in young women 15–25 years old [
12].
We have targeted an accrual of a total of 200 participants (143 girls and 57 boys) to receive the vaccine intervention. With an anticipated attrition rate of 30%, we expect to have at least 100 girls and 39 boys to complete the study with evaluable results.
Study procedures
A schedule of study procedures is presented in Table
1. Participants undergo a pre-study screening evaluation. The legal representative(s) (most often parents and legal guardians) of the participants is required to sign the informed consent form and medical records release form. Participants are asked to sign an assent form. Model consent and assent forms are included in Additional file
3. Participants and their legal representative(s) are interviewed for the participant’s medical history (including age of menarche) and concomitant medication use. Participants are assessed for height, weight, vital signs (temperature, pulse, and blood pressure), and baseline signs and symptoms. Urine pregnancy test is performed on participants who have started menstrual periods. The legal representative(s) complete a questionnaire to collect information on the participant’s parental education attainment and household income.
Table 1
Schedule of study events
Informed Consent/Assent | X | | | | | | | | | | | | |
Parental/Household Questionnaire | X | | | | | | | | | | | | |
Assess Eligibility | X | | | | | | | | | | | | |
Medical History | X | | | | | | | | | | | | |
Age of Menarche, if applicable | X | X | | X | | X | | X | | X | | X | |
Urine Pregnancy Teste | X | X | | | | | | | | X | | Xg | |
Baseline signs and symptoms | X | | | | | | | | | | | | |
Vital Signs | X | Xf | | | | | | | | X | | Xg | |
Weight, Height | X | Xf | | | | X | | | | X | | | |
Concomitant Medications | X | X | | X | | X | | X | | X | | X | |
Blood Collection | | X | | X | | X | | X | | X | | X | |
Priming Vaccine Injection | | X | | | | | | | | | | | |
Booster Injection | | | | | | | | | | X | | Xg | |
Adverse Events | | X | X | X | X | X | X | X | X | X | X | X | X |
Telephone/email/text Contactc | | | X | | X | | X | | X | | X | | X |
Eligible participants and their legal representative(s) return to the clinic for a baseline visit. When feasible, this visit is combined with the pre-study screening evaluation visit. If the baseline visit occurs more than 30 days from the screening visit, participants are reassessed for weight and vital signs. Adverse events and concomitant medications are reviewed and age at menarche and urine pregnancy test, if applicable, are reassessed at the baseline visit unless it occurs on the same day as the screening visit. If a urine pregnancy test is positive, the participant is considered off-study and does not undergo additional study procedures, including vaccination. A baseline blood sample is collected and participants are offered topical anesthetic cream to be applied to the blood collection site prior to the venipuncture. The blood samples undergo on-site serum separation and serum aliquots are stored at − 80 °C until analysis.
Following the blood collection, participants receive the priming injection of GARDASIL® 9. Participants are observed in the clinic for at least 15 min following vaccine administration. Participants and legal representative(s) are instructed to record any illness or injury for two weeks following the vaccine injection, and the diary is mailed back to the study office in a pre-stamped and addressed envelope.
Participants and their legal representative(s) return to the clinic at 6, 12, 18, 24, and 30 months after the priming injection of Gardasil 9. Blood samples are collected from the participants at each visit and processed/stored as the baseline samples. Similarly, participants are offered topical anesthetic cream prior to blood collection. At all visits, participants are assessed for adverse events, concomitant medications, and menarche, if applicable. Weight and height are assessed at the months 12 and 24 visits. For the month 24 and 30 visits, participants also undergo a urine pregnancy test, if applicable. If a urine pregnancy test is positive, the participant is considered off-study and does not undergo additional study procedures, including vaccination. Following the blood collection at the month 24 visit, participants receive the (deferred) booster injection of GARDASIL® 9. At the month 30 visit, the third vaccine dose is offered after the blood collection but is optional. Participants keep a diary of any illness or injury for 2 weeks after each vaccine dose and mail the diary back to the study office in a pre-stamped and addressed envelope provided by the study office.
Participants and their legal representatives are contacted monthly and within two weeks prior to each visit using their preferred method of contact to promote participant retention. Participants and their legal representatives are reminded to refrain from non-study HPV vaccination during the study period.
Dose modification
At the discretion of the study physician, the vaccine injection may be delayed because of a current or recent febrile illness. Low-grade fever itself (temperature < = 100.4) and mild upper respiratory infection are not generally contraindications to vaccination. Participants who develop anaphylactic reactions following the first injection will permanently discontinue Gardasil 9.
Off-agent criteria
Participants may stop receiving study agent for the following reasons: completed the protocol-prescribed procedures, adverse event or serious adverse event, received an HPV vaccine outside the context of the study, inadequate agent supply, noncompliance, concomitant medications, and medical contraindication. Participants will continue to be followed, if possible, for safety reasons and in order to collect endpoint data according to the schedule of events.
Off-study criteria
Participants may go ‘off-study’ for the following reasons: the protocol procedures and any protocol-required follow-up period is completed, adverse event/serious adverse event, lost to follow-up, non-compliance, concomitant medication, medical contraindication, withdraw consent, death, determination of ineligibility (including screen failure), pregnancy, or have received HPV vaccine outside the context of the study.
Data management
Participant data are collected using protocol-specific case report forms (CRF) developed utilizing NCI-approved Common Data Elements (CDE). This study uses the OnCore from Forte Research Systems, Inc. for data collection, reporting and management. Study staff entering data or reviewing data will have appropriate education, training and experience to perform assigned tasks. A quality assurance/quality control plan is implemented to ensure protocol adherence to all aspects of the trial, including obtaining informed consent, verification of eligibility, adherence to protocol, documentation of adverse events, accuracy of transcription between source and CRF, and reporting serious adverse events.
In addition, representatives from the study sponsor conduct annual monitoring visit to review regulatory documents for the study, verify that a signed/dated informed consent is on file for each enrolled participant, review documentation for all reported serious adverse events, visit the Investigational Drug Pharmacy to assess drug accountability, and review participant charts.
Statistical considerations
The primary endpoints are the persistence and stability of serologic geometric mean titer (GMT) of HPV16 and HPV18 between 6, 12, 18, and 24 months after the first dose, prior to the administration of the second dose. A one-sided paired t test will be performed to compare the difference in the mean of the log-transformed type-specific antibody levels between 6- and 12-month visits, between 12- and 18-month visits, and between 18- and 24-month visits respectively, to evaluate whether the type-specific GMT at 12−/18−/24-months, respectively, is not inferior to the GMT at 6−/12−/18-months. Comparing the difference in the mean of the log-transformed type-specific antibody levels is equivalent to comparing the logarithm of the ratio of GMTs since GMT is equal to the exponentiation of log-transformed mean. Bonferroni correction will be used to correct for multiple comparisons.
The protocol was originally designed to assess the serologic response in girls. Addition of a cohort of boys was included in a subsequent protocol expansion amendment. Due to limits in the study completion timelines and available study budgets, fewer boys than girls are included in the study to generate pilot data on the serologic response in boys. We expect boys and girls to have different responses to the vaccine and will perform the primary analyses for girls and boys separately. For girls, with a sample size of 100 and an overall significance level of 5% (based on Bonferroni correction, i.e. a 1.67% significance level for each test), there will be at least 90% power to detect a non-inferiority margin no greater than 0.35 standard deviations [
16]. For boys, with a sample size of 39 and an overall significance level of 5%, there will be at least 80% power to detect a non-inferiority margin no greater than 0.50 standard deviations. In addition, similar to the analysis performed by Safaeian et al. [
17], we will also evaluate the stability by categorizing the changes in antibody level from 6 months to 12 months. Specifically, a participant’s antibody level at 12 months either remains within two-fold of the level at 6 months (considered as stable) or decreases/increases more than two-fold of the level at 6 months (same for the changes from 12 months to 18 months and from 18 months to 24 months). Percentage of participants whose type-specific antibody levels decrease, increase, or remain stable between the 6- and 12-month study visits, between the 12- and 18-month study visits and between the 18- and 24-month study visits will be reported along with the associated 95% confidence interval. For girls, a sample size of 100 will produce a two-sided 95% confidence interval with a width ≤ 0.203 based on the exact method approach. For boys, a sample size of 39 will produce a two-sided 95% confidence interval with a width ≤ 0.328 based on the exact method approach.
HPV 16/18 was singled out for the primary endpoints since it will allow direct comparisons with similar data on type-specific antibody level stability and kinetics from the types present in both the bivalent and quadrivalent vaccines. We were also interested in examining the persistence and stability of serologic GMT of the other HPV types covered by the nonavalent HPV vaccine (i.e., HPV types 6, 11, 31, 33, 45, 52, and 58). As obesity has been associated with lower antibody levels in other vaccines [
18,
19], we propose to perform a linear mixed effects model with body mass index (BMI), time, and the interaction between BMI and time as the covariates on antibody level data measured at 6, 12, 18, and 24 months.
Similar to the primary analyses, we will perform all of the secondary and exploratory analyses separately for girls and boys. For the secondary and exploratory analyses, adjustment for multiple comparisons will not be performed. However, the number of comparisons will be reported and we will cautiously interpret the findings. For both primary and secondary endpoints, if the normality assumption is violated, potential transformation will be sought or nonparametric methods such as signed rank test will be performed.
We will try to reduce the fraction of participants with missing outcomes as much as possible. The covariates (e.g. BMI, body surface area, and sociodemographics) that are predictive of missing-ness for each outcome at each visit (i.e., 6, 12, 18 and 24 months) will be identified through use of logistic regression for each missing indicator and then incorporated into multiple imputation procedures to handle missing data while performing the statistical analysis for both primary and secondary endpoints.
No formal interim statistical analyses are planned for this trial. Accrual, data collection, and any adverse events will be monitored on a regular basis.