This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for HPV Vaccination Study in Postpartum Women (NCT04274153), a na phase 4 study. The primary outcome is Immunogenicity of a Two-dose 9-valent HPV Vaccination as Assessed by Antibody Titer.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT04274153 |
| Phase | Phase 4 |
| Condition | HPV, Immunization, Human Papilloma Virus |
| Allocation | Not applicable (single group) |
| Design model | Single Group |
| Masking | None (open label) |
| Enrollment | 225 |
| Arms in the primary outcome | n/a |
| Lead sponsor | Johns Hopkins University |
| Results posted | Yes |
2. Clinical Question
Population
Postpartum girls and women aged 15–45 years who had not previously been vaccinated against HPV. For the primary antibody-titer analysis, participants whose baseline anti-HPV 16 titer was above the seroconversion limit were excluded; the registry record states that 129 participants were included in that analysis.
Intervention
Gardasil9, the 9-valent HPV vaccine, administered in a two-dose protocol. The doses were scheduled at 0 and 6 months, with an additional dose offered after the final blood draw at 12 months.
Comparator
There was no separate comparison group. The record describes a single-group study, so it does not compare the regimen with a placebo, another vaccination schedule, or an untreated group.
Primary question
What antibody response, measured as geometric mean titer in milli Merck units per milliliter, was observed after a two-dose 9-valent HPV vaccination regimen in postpartum participants previously unvaccinated against HPV 16? The primary endpoint timeframe is up to 23 months.
This is a question about immunogenicity: whether antibody measurements can characterize an immune response after vaccination. It is not a randomized comparative question about differences between treatments. Because there is no separate comparator, any reported antibody response would need to be interpreted as an observed response in the study group, rather than as an estimate of the difference between vaccination and another strategy.
The registry record also lists secondary questions concerning antibody response to the other eight HPV types, HPV 16 seropositivity after one dose and after two doses, baseline titers suggestive of natural inoculation or prior vaccination, and completion of the two-dose schedule. The record does not report results for those questions. It also does not report a numerical result for the primary antibody-titer question.
3. Trial Design
The registry record describes a Phase 4, single-group pilot study sponsored by Johns Hopkins University. It lists planned enrollment of 225 and identifies postpartum women seeking care at Johns Hopkins University as the setting. The study is marked completed. The recorded start date is 2020-08-03, and the primary completion date is 2022-07-01.
Participants were scheduled to receive two doses of the 9-valent HPV vaccine at 0 and 6 months. An additional vaccine dose was to be offered after the final blood draw at 12 months. The primary endpoint timeframe is stated as up to 23 months. The record does not provide individual visit schedules or a detailed account of how the timeframe relates to each participant’s measurements.
A single-group design can describe outcomes observed in participants who received the study regimen. It does not, by itself, separate the effect of the regimen from changes over time, participant characteristics, or other influences. The registry lists allocation as not applicable and masking as none. No randomized allocation between groups is described, and the record does not identify a blinded assessment process.
The study is labeled a pilot study of immunogenicity and acceptability in the postpartum setting. The registry lists six outcome measures, including the primary antibody-titer outcome and secondary measures related to antibody responses, seropositivity, baseline titers, and vaccination completion. It lists 0 analyses. Detailed eligibility criteria beyond the description of postpartum participants, age range, and prior HPV vaccination status are not reported in the registry record. A protocol-level explanation of the sample-size choice, recruitment process, and operational procedures is also not reported in the registry record.
4. Participant Flow and Accounting
The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.
Overall Study
| Stage | Gardasil9 |
|---|---|
| STARTED | 225 |
| COMPLETED | 169 |
| NOT COMPLETED | 56 |
Analysis population for the primary outcome, as defined in the registry: We excluded participants whose anti-HPV 16 titer was above the seroconversion limit and the baseline. Therefore, only 129 were included in this analysis
5. Baseline Characteristics
The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.
| Characteristic | Unit | Gardasil9 |
|---|---|---|
| Participants analysed | 225 | |
| Age, Continuous | years | 29.9 (SD 6.8) |
| Sex: Female, Male: Female | Participants | 225 |
| Sex: Female, Male: Male | Participants | 0 |
| Race/Ethnicity, Customized: Race/Ethnicity – Hispanic/Latino | Participants | 134 |
| Race/Ethnicity, Customized: Race/Ethnicity – Black/African American | Participants | 43 |
| Race/Ethnicity, Customized: Race/Ethnicity – Asian | Participants | 9 |
| Race/Ethnicity, Customized: Race/Ethnicity – White/Caucasian | Participants | 36 |
| Race/Ethnicity, Customized: Race/Ethnicity – Two or more races | Participants | 2 |
| Race/Ethnicity, Customized: Race/Ethnicity – Other | Participants | 1 |
| Region of Enrollment: United States | Participants | 225 |
| Highest level of education: Grade 11 or less | Participants | 71 |
| Highest level of education: Grade 12 to some college | Participants | 99 |
| Highest level of education: Bachelor's degree or higher | Participants | 55 |
| Employed: Yes | Participants | 74 |
| Employed: No | Participants | 151 |
6. Primary Endpoint
The registry lists the primary outcome as Immunogenicity of a Two-dose 9-valent HPV Vaccination as Assessed by Antibody Titer, measured over Up to 23 months.
| Element | Registry entry |
|---|---|
| Result type | Geometric Mean |
| Measure of spread | 95% Confidence Interval |
| Unit | mMU/mL |
| Endpoint classification | not reduced to a single comparison |
The primary endpoint is the immunogenicity of a two-dose 9-valent HPV vaccination regimen, assessed by antibody titer. The measurement is expressed in milli Merck units per milliliter, and the endpoint parameter is the geometric mean. The registry describes a 95% confidence interval as the measure of dispersion and gives a timeframe of up to 23 months.
Antibody titers are laboratory measurements used to characterize an immune response. A geometric mean is a summary suited to measurements that are analyzed on a multiplicative scale; it is not the same summary as an arithmetic average. A confidence interval communicates uncertainty around an estimated quantity, with its interpretation depending on the analysis and assumptions used to construct it. These are general statistical descriptions, not a substitute for an endpoint result.
The record states that participants whose baseline anti-HPV 16 titer was above the seroconversion limit were excluded from the primary analysis, leaving 129 participants included. It does not report the resulting geometric mean titer or its confidence interval. It also does not specify the exact blood-draw schedule used for each primary measurement or explain how measurements from multiple time points were handled. Those details are not reported in the registry record.
The endpoint is an antibody measurement, not a clinical disease outcome. It therefore addresses immunogenicity rather than the occurrence of HPV infection, precancerous lesions, or cancer. The registry record does not provide a threshold for interpreting the primary geometric mean as clinically meaningful.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record contains a design description and endpoint definition, but it does not report the numerical primary endpoint result. In particular, it does not give a geometric mean antibody titer or a 95% confidence interval. As a result, the magnitude and precision of the antibody response cannot be assessed from the registry record. No conclusion about the size of the observed response can be drawn from the endpoint description alone.
The record states that 129 participants were included in the primary analysis after excluding participants whose baseline anti-HPV 16 titer was above the seroconversion limit. This tells readers which number of participants the record associates with that analysis and describes an exclusion rule. It does not provide a participant flow, the number excluded, reasons for any other exclusions, or the amount of missing antibody data. Those details are not reported in the registry record.
Because the study is single-group, it has no concurrently observed comparison group. Even if the antibody result were reported, the study design would support a description of responses in the analyzed participants, not a randomized estimate of how those responses differ from a control condition. Comparisons with outside expectations or other studies would require additional information and assumptions not contained in the registry record.
The record lists secondary outcomes covering antibody response to the other eight HPV types, HPV 16 seropositivity after one dose and after two doses, baseline titers suggestive of natural inoculation or prior vaccination, and completion of the two-dose schedule. Numerical findings for these outcomes are not reported in the registry record. The record lists 0 analyses, and it does not supply inferential statistics or a statistical analysis plan. Therefore, there is no reported basis for assessing statistical evidence, adjusted comparisons, or uncertainty for these secondary questions.
The safety record lists 0 serious adverse events among 225 participants at risk, 1 other adverse event among 225 at risk, and 0 deaths. These are descriptive counts. The record does not provide event details or an assessment of whether an event was related to vaccination. The counts should not be read as evidence that an adverse event is impossible or that the regimen has a particular safety profile beyond the recorded observations.
Overall, the registry record permits a description of the planned regimen, the primary endpoint, the analysis population stated for that endpoint, and the reported safety counts. It does not provide enough outcome information to estimate the antibody response or evaluate its precision, and it does not support a comparative treatment conclusion.
9. Statistical Methods Explained
General statistical context: immunogenicity studies often summarize antibody measurements with a geometric mean when the data are analyzed on a multiplicative scale. The geometric mean is obtained through a transformation-based summary rather than by taking the ordinary arithmetic average. This can be appropriate for positive measurements that vary proportionally, but the registry record does not describe the specific transformation, handling of values below assay limits, or distributional checks used in this study.
What does a geometric mean describe?
A geometric mean summarizes the central level of a set of positive measurements on a multiplicative scale. It can be useful when proportional differences are more meaningful than absolute differences. It does not describe the full spread of individual values, and it should not be interpreted as the response of every participant. The registry identifies the primary parameter as a geometric mean titer in milli Merck units per milliliter, but does not report the estimated value.
What does a confidence interval contribute?
General statistical context: a confidence interval gives a range of values compatible with an estimate under the assumptions of the method used to construct it. It conveys precision; a narrower interval generally indicates more precise estimation than a wider one, all else equal. It does not establish that an estimate is clinically important, and it is not a guarantee that the true value lies in the particular interval. The record names a 95% confidence interval as the dispersion measure for the primary endpoint, but the interval itself is not reported in the registry record. The method used to calculate it is also not reported in the registry record.
Why does the single-group design matter?
General statistical context: a single-group study can estimate or describe outcomes among people observed under a regimen. Without a concurrent comparison group, however, it cannot directly estimate a between-group treatment contrast. Changes in measurements over time may reflect the regimen, but could also reflect other influences. Randomization is one way to balance measured and unmeasured factors between comparison groups; the record does not describe randomized allocation in this study. The record identifies the study as single group, with allocation not applicable and no masking.
The registry describes scheduled vaccine doses at 0 and 6 months and an additional dose offered after the final blood draw at 12 months. The primary endpoint timeframe is up to 23 months. General statistical context: measurements collected at multiple times can be analyzed as separate time-specific summaries or with a model that accounts for within-participant correlation. The record does not state which approach was used, whether all planned time points contributed to the primary endpoint, or whether the primary question was evaluated at a particular visit.
What does the analysis population mean?
The primary analysis description excludes participants whose baseline anti-HPV 16 titer was above the seroconversion limit and states that 129 participants were included. This criterion can affect which participants contribute to the endpoint summary. General statistical context: defining an analysis population matters because estimates apply most directly to the people included and the measurements analyzed. The record does not explain how the threshold was established, whether the exclusion rule was prespecified, or how participants with missing baseline or follow-up measurements were handled.
The registry lists 225 as the planned enrollment and 129 as the number included in the primary analysis. These are different quantities: planned enrollment describes the intended study size, while the primary analysis count describes the stated endpoint population. The registry does not provide enough participant-flow information to account for the relationship between them. A numerical explanation of the difference is not reported in the registry record.
What can the safety counts establish?
General statistical context: event counts describe what was recorded in the observed group, but a count of zero does not prove that an event cannot occur. The interpretation depends on the observation period, event definitions, completeness of follow-up, and whether events were actively collected. The registry reports 0 serious adverse events, 1 other adverse event, and 0 deaths among 225 participants at risk for the respective categories. Event definitions, follow-up completeness, and causal assessments are not reported in the registry record.
The record also lists 0 analyses. It does not provide methods for estimating confidence intervals, testing hypotheses, addressing repeated measurements, adjusting for baseline titers, or examining subgroups. General statistical concepts can clarify what such methods would do, but the registry record does not establish that any particular method was used. A sample-size rationale and any interim-analysis plan are not reported in the registry record.
10. Multiplicity, Missing Data and Analysis Populations
The registry record lists six outcome measures, including the primary antibody-titer endpoint and secondary outcomes involving responses to other HPV types, HPV 16 seropositivity after one and two doses, baseline titers suggestive of natural inoculation or prior vaccination, and completion of the two-dose regimen. It lists 0 analyses. The record does not state whether any outcome was prioritized for formal hypothesis testing or whether adjustment for multiple comparisons was planned.
General statistical context: when several outcomes or time points are examined, the chance of at least one apparently unusual result can increase if each is assessed separately using conventional statistical thresholds. A prespecified hierarchy or multiplicity adjustment can help control how results are interpreted. The registry record does not report a hierarchy, adjustment method, or related rationale. No multiplicity-adjusted results are reported in the registry record.
The primary analysis description states that participants with a baseline anti-HPV 16 titer above the seroconversion limit were excluded and that 129 participants were included. This is the only stated detail about the primary analysis population. The record does not describe how missing antibody measurements were handled, whether participants were excluded for other reasons, or whether the analysis used all available observations or a restricted set of complete observations. A missing-data strategy is not reported in the registry record.
The record does not report how missing secondary outcome data were handled, how vaccination completion was defined, or how participants who did not receive both scheduled doses contributed to outcome summaries. It also does not state whether the exclusion criterion was specified before data review. These omissions limit assessment of how selection and incomplete follow-up may affect the reported analyses. Since numerical outcome analyses are not reported, the consequences cannot be evaluated from the registry record.
11. Safety Results
The registry reports serious adverse events as affected participants divided by participants at risk.
| Arm | Participants with serious adverse events | Participants at risk | Percentage |
|---|---|---|---|
| Gardasil9 | 0 | 225 | 0.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Gardasil9 | 0 of 225 |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 0% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Gardasil9 | 1 of 225 |
Most frequent non-serious adverse event terms
| Event term | Organ system | Gardasil9 |
|---|---|---|
| Not serious adverse event due to medication | Skin and subcutaneous tissue disorders | 1 of 225 |
The registry record lists 225 participants at risk for serious adverse events and reports 0 affected by a serious adverse event. It lists 225 participants at risk for other adverse events and reports 1 affected. It reports 0 deaths. No serious adverse event terms are listed.
These figures are descriptive counts for the categories recorded in the registry. They do not provide information about event types beyond the absence of listed serious terms, severity among the other adverse event category, timing, duration, outcome, or attribution to vaccination. Those details are not reported in the registry record.
General statistical context: a count of zero in an observed study group is not proof of zero underlying risk. Its interpretation depends on the size and follow-up of the observed group, how events were defined and collected, and whether all relevant events were reported. The registry record does not give enough detail to assess those factors. The counts also do not establish how the regimen compares with another schedule or with no vaccination, because the study has no separate comparator group.
The safety figures should therefore be read as the registry’s reported event counts, not as a comprehensive estimate of comparative safety or a guarantee about future participants. The record does not report an assessment of whether the one other adverse event was related to vaccination.
12. What the Result Does, and Does Not, Mean
The registry record describes a pilot study of a two-dose 9-valent HPV vaccination regimen in postpartum participants and specifies an antibody-titer measure as its primary endpoint. It also states that 129 participants were included in the primary analysis after excluding participants with baseline anti-HPV 16 titers above the seroconversion limit. These details define the intended scientific question and the stated analysis population.
The record does not report the primary geometric mean titer or its 95% confidence interval. It therefore does not show the observed magnitude or precision of the antibody response. Results for the listed secondary outcomes are not reported in the registry record either. Without those values, the endpoint description cannot be treated as evidence for a particular level of response or a change in response across time.
The study is single group, with no separate comparator. Consequently, even a reported antibody result would describe the participants’ observed measurements rather than a randomized difference between treatment strategies. The record does not include a reported comparison with another vaccination schedule, a placebo, or an untreated group.
The primary endpoint is an immunogenicity measure, not a clinical outcome such as HPV infection or disease. Antibody measurements can characterize an immune response, but the registry record does not establish a clinical threshold for interpreting the endpoint. No conclusion about clinical benefit should be inferred from the endpoint definition alone.
The safety counts report 0 serious adverse events among 225 at risk, 1 other adverse event among 225 at risk, and 0 deaths. They describe events recorded in this study and do not establish comparative safety, event relatedness, or the absence of risk. In short, the record supplies useful information about study design, endpoint selection, analysis population, and recorded safety counts, but does not report enough efficacy-related outcome data to characterize the primary result.
13. Why This Trial Matters Statistically
Statistically, this study raises a practical question about measuring antibody responses in a postpartum setting using a two-dose schedule. The registry identifies a specific population, intervention, antibody-based primary endpoint, and analysis population. These elements help readers understand what the study was designed to describe, even though numerical primary results are not reported.
The study also illustrates the distinction between an endpoint definition and an endpoint finding. Naming a geometric mean titer and a 95% confidence interval describes the planned summary and uncertainty measure; it does not reveal the estimated response or its precision. For a reader assessing evidence, the absence of those numerical results is consequential: the central immunogenicity question cannot be evaluated from this registry record.
The stated exclusion based on baseline anti-HPV 16 titer is another important statistical feature. It means the primary analysis population is defined in part by a baseline measurement. Readers need to know who was included, how the threshold was set, and how missing measurements were handled to understand the scope and potential selection effects of an estimate. The record provides the included count and the exclusion description, but further details are not reported in the registry record.
The single-group design is relevant to interpretation as well. It can support a description of observed antibody measurements, but it does not furnish a randomized contrast. This distinction prevents an observed outcome from being mistaken for a comparative treatment effect. The registry’s focus on immunogenicity and acceptability is also distinct from a direct assessment of clinical disease outcomes.
Finally, the safety counts show why event definitions, follow-up, and attribution matter when interpreting registry figures. The recorded counts are useful descriptive information, but they do not answer comparative safety questions. Together, these features make the registry record informative about the design and limits of the evidence, while leaving the primary outcome magnitude and uncertainty unresolved.
14. Limitations
- The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
- Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.
The main limitation for statistical interpretation is that the registry record does not report the numerical primary endpoint estimate or its 95% confidence interval. It also does not report numerical findings for the secondary outcomes. Without these results, the antibody response and its precision cannot be described.
The single-group design lacks a concurrent comparator, so the record cannot support a randomized between-group contrast. Masking is listed as none, and allocation is listed as not applicable. The record does not describe additional safeguards for outcome assessment or laboratory measurement.
The primary analysis includes 129 participants after excluding participants whose baseline anti-HPV 16 titer was above the seroconversion limit. The registry does not report a complete participant flow, the number excluded under this rule, other reasons for non-inclusion, or how missing measurements were handled. It also does not explain how the seroconversion threshold was established or whether the exclusion was prespecified.
The registry states a primary timeframe of up to 23 months, but does not describe which measurements within that timeframe contributed to the primary summary or how repeated measurements were analyzed. The statistical analysis plan, sample-size justification, interim analyses, and multiplicity approach are not reported in the registry record.
Safety information is limited to counts of serious adverse events, other adverse events, and deaths. Event descriptions, collection procedures, follow-up completeness, and relatedness assessments are not reported. These limitations mean that the available record gives a concise outline of the study and its outcomes of interest, but does not provide the information needed for a full evaluation of the analysis or its findings.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: HPV Vaccination Study in Postpartum Women — NCT04274153.
- Registry record last updated 2023-08-29; status last verified 2023-08.
- Results first posted 2023-08-29.
- Data retrieved from ClinicalTrials.gov on 2026-11-09.
- Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.
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18. Record Summary
This completed Phase 4 pilot study is described as a single-group evaluation of a two-dose 9-valent HPV vaccination regimen in postpartum girls and women aged 15–45 years who were previously unvaccinated against HPV. The planned enrollment was 225. Vaccine doses were scheduled at 0 and 6 months, with an additional dose offered after the final blood draw at 12 months.
The primary outcome was antibody response summarized as a geometric mean titer in milli Merck units per milliliter, with a 95% confidence interval and a timeframe of up to 23 months. The record states that 129 participants were included in the primary analysis after excluding those whose baseline anti-HPV 16 titer was above the seroconversion limit. The primary numerical result and results for the listed secondary outcomes are not reported in the registry record.
The safety record lists 0 serious adverse events among 225 at risk, 1 other adverse event among 225 at risk, and 0 deaths. The study has no separate comparator group, and the statistical analysis plan and missing-data methods are not reported in the registry record.