The Effect of HPV Vaccination on Recurrence Rates in HIV Patients With Condylomata: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for The Effect of HPV Vaccination on Recurrence Rates in HIV Patients With Condylomata (NCT00941889), a randomized na study. The primary outcome is The Primary Endpoint of This Study is Persistence and Recurrence of Anal Warts as Compared Between the Experimental and Control Groups..

2. Clinical Question

The registry describes persistence as the presence of any lesions at the one-month follow-up after surgery. Recurrence is defined as the development of new lesions after one month of follow-up. The primary endpoint combines these clinical concepts in a comparison of the experimental and control groups. Its stated follow-up evaluations occurred at 1, 3, 6, 9, 12, 15 and 18 months after initial treatment.

The record posts a count of 1.0 for each group, with five placebo participants and seven Gardasil participants represented in the endpoint data. These counts do not, by themselves, show that the groups had the same event frequency: the group sizes differ, and the record does not provide an estimable two-arm comparison. It also does not report an inferential estimate or uncertainty interval. The clinical question is therefore clear, but the posted results do not establish the magnitude or precision of a group difference.

3. Trial Design

This completed pilot study is recorded as randomized, double-masked and parallel-group. It enrolled 32 participants, with HIV infection and anal condylomata among the listed conditions. The registry labels the phase as NA. Washington University School of Medicine is listed as the sponsor. The study began in 2007-07, and primary completion is recorded as 2011-07.

Participants were assigned to saline placebo or quadrivalent HPV vaccine. The placebo group received saline in the upper extremity at the initial visit, two months and six months after enrollment. The Gardasil group received a 0.5mL intramuscular vaccine injection at those same scheduled times. The record identifies the objective as evaluating the vaccine's effect on anal condylomata recurrence and persistence in HIV-positive patients.

The primary outcome is a binary event count: participants with persistence or recurrence of anal warts. Persistence refers to lesions at the one-month post-surgery follow-up; recurrence refers to new lesions developing after one month of follow-up. The stated assessment schedule extends through 18 months after initial treatment, with evaluations at 1, 3, 6, 9, 12, 15 and 18 months.

Although the trial enrolled 32 participants, the endpoint population described in the record consists of five placebo-group participants and seven Gardasil-group participants who completed all three injections per protocol. The remaining patients did not complete required follow-up and could not be analyzed. The registry does not report further detail about the allocation procedure, concealment, masking procedures, planned sample-size justification, or the full statistical analysis plan. Randomized and double-masked describe the listed design; they do not resolve the limitations of the small endpoint population or missing follow-up.

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

Analysis population for the primary outcome, as defined in the registry: Five patients from the placebo group and seven patients from the gardasil group completed all three injections per the protocol. The remaining patients did not complete study-required follow-up and therefore could not be analyzed. One patient from the Gardasil Group and one patient from the placebo group met the outcome measure of recurrence.

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.

Population: Baseline characteristics were reported (age, gender, region of enrollment). Five of 17 patients in the placebo group completed study follow-up through at least 6 months and received all three study injections. Seven of 15 patients in the Gardasil group completed study follow-up through at least 6 months and received all three study injections.

6. Primary Endpoint

The registry lists the primary outcome as The Primary Endpoint of This Study is Persistence and Recurrence of Anal Warts as Compared Between the Experimental and Control Groups., measured over Follow up evaluation after treatment at 1, 3, 6, 9. 12, 15, 18 months after initial treatment.

The primary endpoint concerns persistence or recurrence of anal warts following treatment for anal condylomata. The record defines persistence as the presence of any lesion at one month after surgery, and recurrence as development of new lesions after one month of follow-up. This endpoint is recorded as a participant count, rather than a continuous measurement.

These outcomes represent distinct patterns over time: a lesion may remain present at the early assessment, while new lesions may emerge later. Tracking both allows the study question to address continued or renewed disease rather than only the immediate post-surgical finding. The registry states that follow-up evaluations were scheduled at 1, 3, 6, 9, 12, 15 and 18 months after initial treatment. However, it does not describe how the combined endpoint was operationalized across those visits, how a participant with both persistence and recurrence was counted, or how incomplete visit histories were handled. Those details are not reported in the registry record.

The posted data list 1.0 participant with the event in each group. A count alone does not communicate how common the event was within each group, especially because the reported group sizes differ. More importantly, the record states that values needed for a two-arm binary comparison are missing or not estimable. No comparative effect estimate or uncertainty interval is posted. The endpoint is relevant to the study objective, but its reported summary is insufficient to quantify a reliable contrast between groups.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does a binary endpoint count?

A binary endpoint classifies each participant according to whether a defined event occurred. For this trial, the recorded event concerns persistence or recurrence of anal warts. The registry reports participant counts, not lesion counts or a continuous measure of disease. In a two-arm study, a useful comparison ordinarily needs the event information and the number of participants assessed in each group. This permits an estimate of how frequently the event occurred in each group and a measure of uncertainty around the contrast.

The registry lists 1.0 event participant in each group and identifies the analyzed group sizes as five and seven. It also states that the values necessary for a two-arm binary comparison were missing or not estimable. Therefore, there is no posted comparative estimate to interpret. The numerical equality of the event counts is not itself a comparison of group frequencies, and it cannot replace an analysis that accounts for the different denominators.

What would an uncertainty interval tell a reader?

General statistical explanation: a confidence interval describes a range of values compatible with the observed data and the assumptions of a statistical method. A narrow interval generally conveys greater precision than a wide interval. For a two-group binary outcome, an interval could express uncertainty around an effect measure, such as a difference between group event proportions or a ratio of those proportions. The registry does not post such an estimate or interval for this endpoint. No conclusion about the precision of a comparative effect can therefore be drawn from an interval.

A p-value, if reported, would address how compatible the data are with a specified null hypothesis under the assumptions of the test. It would not quantify the size of an effect or establish clinical importance. No p-value or analysis result is posted for the primary endpoint. The record also does not report the planned test or the prespecified threshold used for primary inference. The significance level of 0.05 appears only among assumptions for planning illustrations, not as a reported analysis result from this trial.

Why does missing follow-up matter?

General statistical explanation: when participants lack outcome assessments, the analyzed group may no longer preserve the balance created by randomization. This can occur if missingness is related to participant characteristics, treatment assignment or the unobserved outcome. Even when the reasons are unrelated to outcome, fewer observed participants generally mean less information and less precise estimates. These concerns make it important to report how many participants were assessed, why data are missing, and how missing outcomes were handled.

In this record, five placebo participants and seven Gardasil participants completed all three injections per protocol. The remaining patients did not complete required follow-up and could not be analyzed. The record does not report a missing-data method, an intention-to-treat analysis, or a comparison of participants with and without complete follow-up. It also does not provide a visit-by-visit accounting of missing observations. Without those details, the impact of incomplete follow-up on the endpoint comparison cannot be assessed.

How should the planning illustrations be read?

General statistical explanation: sample-size planning relates a target effect, variability or event frequency, significance level, allocation, and desired power to the number of participants needed under stated assumptions. A planning calculation based on an observed effect is not the same as the trial's original design justification. It is also not a measure of the probability that this completed study detected a true effect. Such calculations are particularly sensitive when the observed endpoint is based on few participants, because small changes in sparse data can substantially alter the estimated effect used for planning.

The planning illustrations associated with this study are described as using the observed effect, a two-sided significance level of 0.05, equal allocation, a normal approximation, and target effects expressed as fractions of the observed effect. They are planning illustrations, not reported design assumptions for the original trial and not observed power. The registry does not report its original sample-size justification. Since the two-arm endpoint comparison is listed as not estimable, any planning exercise based on that contrast should be interpreted cautiously and cannot supply the missing primary analysis.

What analysis details remain unknown?

The registry record does not report a statistical analysis plan, a method for adjusting for baseline characteristics, handling of repeated follow-up assessments, or a method for combining persistence and recurrence. It also does not report an interim analysis plan or a model for the primary endpoint. Those omissions should not be filled by assuming a familiar method. The record supports description of the randomized design and the posted counts, but it does not support reconstruction of a comparative analysis.

10. Exact Estimates for Each Arm

No two-arm comparison is shown for this trial, but each arm's result can still be summarized with exact interval estimates computed from the posted counts. The Clopper-Pearson interval is exact and conservative; the Wilson interval is a common closer-to-nominal alternative; the Bayesian credible interval uses a uniform Beta(1, 1) prior. For small groups the three can differ noticeably.

R code and output

arm    <- c("Placebo Group", "Gardasil Group")
n      <- c(5, 7)
events <- c(1, 1)
for (i in seq_along(n)) {
  ci <- binom.test(events[i], n[i])$conf.int          # Clopper-Pearson exact interval
  cr <- qbeta(c(0.025, 0.975), 1 + events[i], 1 + n[i] - events[i])   # Bayesian, uniform Beta(1,1) prior
  wi <- (function(x, n) { p <- x / n; z <- qnorm(0.975); d <- 1 + z^2 / n
    c((p + z^2 / (2 * n) - z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d, (p + z^2 / (2 * n) + z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d) })(events[i], n[i])
  cat(sprintf("ARM|%s|%d|%d|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f\n", arm[i], n[i], events[i], 100 * events[i] / n[i],
              100 * ci[1], 100 * ci[2], 100 * wi[1], 100 * wi[2], 100 * cr[1], 100 * cr[2]))
}

ARM  Placebo Group  5  1  20.0  0.5  71.6  3.6  62.4  4.3  64.1
ARM  Gardasil Group  7  1  14.3  0.4  57.9  2.6  51.3  3.2  52.7

11. Multiplicity, Missing Data and Analysis Populations

The primary endpoint includes persistence and recurrence, and follow-up evaluations are listed at 1, 3, 6, 9, 12, 15 and 18 months after initial treatment. The registry does not explain whether the assessments were treated as separate outcomes, whether one time point was designated for the principal comparison, or how the two endpoint components were combined for analysis. It also does not report a multiplicity strategy. Without these details, the impact of testing or interpreting multiple time points or outcome components cannot be assessed.

The record says that five placebo-group patients and seven Gardasil-group patients completed all three injections per protocol. Remaining patients did not complete study-required follow-up and could not be analyzed. It does not report detailed reasons for incomplete follow-up, the number of missing outcome assessments at each visit, or how missingness was addressed statistically. No imputation or other missing-data method is described. The record also does not report an intention-to-treat analysis or an alternative analysis population.

These limitations matter because an analysis restricted to participants with complete treatment and follow-up can differ from an analysis retaining everyone as randomized. If missing outcomes are related to the chance of persistence or recurrence, the complete-case summary may not represent the enrolled groups. The registry does not provide enough information to determine whether such selection affected the posted endpoint counts.

The posted endpoint results do not include an estimable two-arm binary comparison. The registry does not report a prespecified analysis plan, adjustment for multiple comparisons, or sensitivity analyses. These are not details that can be reconstructed from the equal event counts. The available record therefore permits a description of the incomplete endpoint population and counts, but not an assessment of how multiplicity and missing data were managed in the study's intended inference.

12. What the Result Does, and Does Not, Mean

The posted results show that the endpoint count was 1.0 participant in each group among the participants represented in the endpoint data. Five placebo participants and seven Gardasil participants are listed as completing all three injections per protocol. The record says that remaining patients did not complete required follow-up and could not be analyzed. These statements describe the available result; they do not establish a treatment effect.

The equal counts do not show that the groups had equivalent outcomes. Their analyzed sizes differ, and the registry states that values for a two-arm binary comparison were missing or not estimable. The record provides no comparative effect estimate, confidence interval or p-value. Thus, the direction and precision of any difference cannot be determined from the posted analysis.

Nor does the absence of a reported comparison establish that there was no effect. A non-estimable result is not a finding of no difference. It means that the registry record does not furnish a statistical comparison from which to evaluate the primary question. The counts are too limited, on their own, to support claims about the magnitude of recurrence or persistence in either group.

The trial is recorded as randomized and double-masked, but those design features do not answer the question of how missing follow-up affected the observed groups. The record does not report enough detail to establish how the observed endpoint population relates to all enrolled participants or how missing outcomes were handled.

These data also do not establish broader clinical effects beyond the specified endpoint, and the registry record does not report a complete safety analysis. The appropriate statistical reading is narrow: the study planned to compare persistence and recurrence, but the posted primary endpoint summary does not permit a reliable group comparison. It should not be used to claim benefit, lack of benefit, equivalence or harm.

13. Why This Trial Matters Statistically

This study illustrates a central issue in clinical trial interpretation: randomization and masking are important design features, but an interpretable result also depends on adequate outcome data and a reported analysis. The record describes a randomized, double-masked comparison, yet the endpoint data represent only five placebo participants and seven Gardasil participants who completed all three injections per protocol. The remaining patients could not be analyzed because they did not complete required follow-up.

The primary event is clinically framed as persistence or recurrence, but the registry posts only a count of 1.0 in each group and states that a two-arm binary comparison was not estimable. This makes clear why counts must be interpreted alongside denominators and a valid comparative estimate. Equal event counts across differently sized groups do not establish equal risks, and counts alone cannot communicate uncertainty.

The record also underscores why transparent reporting of participant flow, missing-data methods, endpoint definitions and analysis plans is essential. The endpoint description identifies persistence at one month after surgery and recurrence as new lesions after one month, while scheduled follow-up extends through 18 months. The record does not explain how these components and repeated assessments were combined in analysis. Readers cannot safely infer a method that is not documented.

Finally, planning calculations based on an observed effect are distinct from original design justification and do not indicate observed power. This distinction matters especially when the endpoint comparison is not estimable and the observed data are sparse. The study is statistically informative as an example of the gap between a stated trial question and the information available for answering it, while leaving the comparative effect 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 primary limitation is that the posted endpoint comparison is not estimable. The record provides an event count of 1.0 in each group, but does not provide a comparative estimate or uncertainty interval. The group sizes represented in the endpoint results are five for placebo and seven for Gardasil, so the equal counts cannot be read as equal event frequencies.

The endpoint population is substantially narrower than the enrolled population: 32 participants were enrolled, while five placebo participants and seven Gardasil participants completed all three injections per protocol. The record states that the remaining patients did not complete study-required follow-up and could not be analyzed. It does not give detailed reasons for non-completion, a full participant disposition by group, or a sensitivity analysis addressing missing outcomes.

The endpoint definition leaves analytical questions unresolved. Persistence is defined by lesions at the one-month assessment after surgery, and recurrence by new lesions after one month of follow-up. The record does not describe how both components were handled for a participant, which follow-up visit governed the primary comparison, or how repeated assessments were used. The planned statistical method and multiplicity approach are not reported in the registry record.

The record also does not report baseline characteristics for the analyzed groups, the original sample-size justification, or a complete analysis plan. Adverse-event fields list zero participants at risk and zero affected in each group, but this does not establish that no adverse events occurred; the record does not provide enough context to interpret those entries as a complete safety assessment. Taken together, these limitations constrain interpretation to the sparse descriptive endpoint counts and leave the primary comparative question unanswered.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: The Effect of HPV Vaccination on Recurrence Rates in HIV Patients With Condylomata — NCT00941889.
• Registry record last updated 2016-07-25; status last verified 2016-06.
• Results first posted 2016-07-25.
• 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.

18. Record Summary

The registry describes a completed randomized, double-masked, parallel pilot study of quadrivalent HPV vaccine versus saline placebo in HIV-positive patients treated for anal condylomata. Enrollment was 32. The primary question concerned persistence or recurrence of anal warts during follow-up extending through 18 months after initial treatment.

Five placebo participants and seven Gardasil participants completed all three injections per protocol; other patients did not complete required follow-up and could not be analyzed. The posted primary endpoint count is 1.0 participant in each group. The registry states that values for a two-arm binary comparison were missing or not estimable, and it reports no comparative estimate or uncertainty interval.

The record does not report the original sample-size justification, detailed missing-data methods, or the primary statistical analysis plan. The posted counts therefore describe a limited endpoint population but do not answer the comparative treatment question.