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 HIV Vaccine Trial in Thai Adults (NCT00223080), a randomized phase 3 study. The primary outcome is Kaplan-Meier Estimate of HIV-1 Infection Rate in Intent to Treat Population.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT00223080 |
| Phase | Phase 3 |
| Condition | HIV Infection |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | Triple |
| Enrollment | 16402 |
| Arms in the primary outcome | n/a |
| Lead sponsor | U.S. Army Medical Research and Development Command |
| Results posted | Yes |
2. Clinical Question
Population
Healthy Thai adults who were HIV-uninfected at entry. The primary endpoint description specifies a modified intent-to-treat population of participants who were infection-free at study entry.
Intervention
ALVAC-HIV vCP1521 plus AIDSVAX, administered intramuscularly on weeks 0, 4, 12, and 24.
Comparator
ALVAC placebo plus AIDSVAX placebo. ALVAC placebo was also administered on weeks 0 and 4.
Primary question
Whether the vaccine regimen changed the estimated HIV-1 infection rate over 42 Months compared with the placebo regimen.
The trial’s stated purpose was to determine whether this combination of immunizations prevented HIV infection in healthy Thai volunteers. The registry describes infection detection using an HIV diagnostic algorithm that employed serologic and nucleic acid technologies, and says infection incidence was compared between vaccine and placebo recipients. That describes the question and the planned endpoint, not the result. The registry record does not report the arm-specific Kaplan-Meier estimates or a numerical comparison, so the size and precision of any difference cannot be assessed from the information reported.
3. Trial Design
This was a Phase III randomized, triple-masked, parallel-group trial of the vaccine regimen and placebo regimen. The registry lists an enrollment of 16402 and identifies HIV Infection as the condition under study. The sponsor was the U.S. Army Medical Research and Development Command. The study began in 2003-10, had primary completion in 2006-07, and is listed as completed.
Participants assigned to the vaccine group were scheduled to receive ALVAC-HIV vCP1521 and AIDSVAX by the intramuscular route on weeks 0, 4, 12, and 24. The placebo group received ALVAC placebo and AIDSVAX placebo on weeks 12 and 24, with ALVAC placebo also administered on weeks 0 and 4. These schedules describe the assigned regimens; the registry record does not give adherence or dose-completion information.
Randomization indicates assignment by chance, while parallel design means the assigned groups were followed as distinct groups. Triple masking indicates that the study was described as masked at three levels, but the registry record does not identify which roles were masked or provide further details about implementation. The primary endpoint description refers to a modified intent-to-treat population restricted to participants who were infection-free at entry. The record’s primary measure title uses the phrase intent to treat, so the population terminology is not fully consistent within the 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.
Before assignment: 16,402 individuals were randomly assigned to the 2 treatment arms. 7 individuals were identified as having human immunodeficiency virus (HIV) infection that was present pre-vaccination detected by polymerase chain reaction (PCR) amplification. These individuals were removed from the modified intent to treat (MITT) population.
Overall Study
| Stage | Vaccine | Placebo |
|---|---|---|
| STARTED | 8197 | 8198 |
| COMPLETED | 7401 | 7401 |
| NOT COMPLETED | 796 | 797 |
Reasons for not completing this period:
| Reason | Vaccine | Placebo |
|---|---|---|
| Withdrawal by Subject | 253 | 232 |
| Required contraindicated med | 0 | 1 |
| Non-compliant | 7 | 7 |
| Moved from study area | 37 | 47 |
| Lost to Follow-up | 259 | 284 |
| Death | 85 | 74 |
| Other | 14 | 11 |
| Reason not provided | 141 | 140 |
| Adverse Event | 0 | 1 |
Analysis population for the primary outcome, as defined in the registry: Modified Intent-to-Treat (MITT) Population: those participants who were infection free at entry into the study
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: Modified Intent to Treat (MITT) Population - those participants who were infection free at entry into the study
| Characteristic | Unit | Vaccine | Placebo | Total |
|---|---|---|---|---|
| Participants analysed | 8197 | 8198 | 16395 | |
| Age, Customized: 18 - 20 | Participants | 2297 | 2246 | 4543 |
| Age, Customized: 21 - 25 | Participants | 3633 | 3708 | 7341 |
| Age, Customized: 26 - 30 | Participants | 2267 | 2244 | 4511 |
| Sex: Female, Male: Female | Participants | 3164 | 3167 | 6331 |
| Sex: Female, Male: Male | Participants | 5033 | 5031 | 10064 |
| Province: Chon Buri | participants | 4107 | 4107 | 8214 |
| Province: Rayong | participants | 4090 | 4091 | 8181 |
| Marital status: Single | participants | 3353 | 3338 | 6691 |
| Marital status: Married | participants | 4110 | 4169 | 8279 |
| Marital status: Divorced | participants | 602 | 541 | 1143 |
| Marital status: Widowed | participants | 50 | 64 | 114 |
| Marital status: Separated | participants | 82 | 86 | 168 |
| Number of sex partners: 0 | participants | 1864 | 1801 | 3665 |
| Number of sex partners: 1 | participants | 5428 | 5495 | 10923 |
| Number of sex partners: > 1 | participants | 619 | 620 | 1239 |
| Number of sex partners: Did not answer | participants | 280 | 273 | 553 |
| Number of sex partners: Missing data | participants | 6 | 9 | 15 |
| Risk group: Low | participants | 3865 | 3924 | 7789 |
| Risk group: Medium | participants | 2369 | 2292 | 4661 |
| Risk group: High | participants | 1963 | 1982 | 3945 |
6. Primary Endpoint
The registry lists the primary outcome as Kaplan-Meier Estimate of HIV-1 Infection Rate in Intent to Treat Population, measured over 42 Months.
| Element | Registry entry |
|---|---|
| Result type | Number |
| Measure of spread | 95% Confidence Interval |
| Unit | Percetage of subjects |
| Endpoint classification | not reduced to a single comparison |
The primary measure is a Kaplan-Meier estimate of HIV-1 infection rate over 42 Months, expressed in the record as a percentage of subjects. The endpoint description defines infection using an HIV diagnostic algorithm employing serologic and nucleic acid technologies. It also states that infection incidence was compared between vaccine and placebo recipients. Although the measure title refers to an intent-to-treat population, its population description specifies a modified intent-to-treat group: participants who were infection-free when they entered the study.
General: A time-to-event endpoint uses both whether an event occurred and when it occurred during follow-up. Kaplan-Meier estimation can account for participants whose event time is not observed through the entire follow-up, by incorporating the time they were observed before follow-up ended. This makes it a common approach when follow-up time varies or when some participants have no recorded event before observation ends. The method does not, by itself, establish why events differ between groups.
The registry record identifies the endpoint and its 95% confidence interval as the dispersion measure, but does not report the arm-specific estimates or interval limits. Thus, the endpoint definition is available, while its numerical result and precision are not reported in the registry record.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record establishes the trial question, assigned regimens, primary endpoint definition, and selected safety counts. It does not provide a numerical arm-specific HIV-1 infection rate, a confidence interval, or a numerical between-group comparison. Consequently, the posted information does not permit a quantitative assessment of the direction, magnitude, or precision of the primary endpoint result. The presence of a specified 95% confidence interval as the dispersion measure does not supply the interval’s limits.
The primary measure is described as a Kaplan-Meier estimate over 42 Months for participants who were HIV-free at entry. That is important context: it indicates a time-to-event outcome and a defined analysis population, rather than a simple count of all enrolled participants. However, the record does not report how many infections occurred in each arm, the estimated rates, or the numbers remaining under observation over time. No rate comparison can be reconstructed from the enrollment and safety figures.
The record lists 16402 participants enrolled and adverse-event group counts of 8197 for Vaccine and 8198 for Placebo at risk for serious events and for other events. Those safety denominators are not a substitute for endpoint analysis denominators or follow-up information. The record does not state whether each safety denominator matches the primary endpoint population.
Seven outcome measures are listed, but the record reports zero analyses. The primary outcome also has several categories or time points and is not reduced to one comparison in the available result description. This means the available information does not establish which estimate should be treated as the single headline contrast, nor whether results were adjusted for other analyses. An effect estimate, a confidence interval, and a clearly specified comparison are needed to assess how compatible the observed data are with different effect sizes.
Accordingly, the numerical evidence should be described as incomplete in this registry record. The absence of a reported estimate is not evidence that the two groups had the same infection experience, and it is not evidence of a particular treatment effect. It is a limit on what can be concluded from the posted information.
9. Statistical Methods Explained
What does randomization contribute?
General: Random assignment is intended to make comparison groups similar, on average, with respect to measured and unmeasured characteristics at the start of a trial. This supports a causal interpretation of a between-group contrast when the trial is conducted and analyzed appropriately. It does not guarantee identical groups, eliminate chance imbalances, or resolve problems caused by missing follow-up or deviations from assigned treatment. The registry identifies the allocation as randomized, but does not report the randomization sequence method, allocation concealment procedures, or any stratification factors.
What does masking mean for interpretation?
The trial is listed as triple-masked. General: Masking can reduce the risk that knowledge of assigned group influences participant behavior, clinical decisions, outcome ascertainment, or assessment. The specific roles masked and the procedures used to maintain masking are not reported in the registry record. The label alone therefore does not establish how masking operated in practice or whether it remained intact.
Why use a Kaplan-Meier estimate?
General: A Kaplan-Meier estimate describes event-free experience over time while allowing participants to contribute information up to the time they leave observation or follow-up ends. Participants who have not had an event by their last observed time are typically treated as censored at that point, rather than as if they remained event-free indefinitely. This approach relies on assumptions about censoring, including that the censoring process does not systematically conceal a different event risk after accounting for the analysis. The registry record names Kaplan-Meier estimation but does not report censoring counts, follow-up completeness, or checks of assumptions.
The endpoint is HIV-1 infection, defined through a diagnostic algorithm using serologic and nucleic acid technologies. General: A prespecified diagnostic definition helps make outcome classification more consistent. The record does not provide the detailed algorithm, adjudication procedures, or timing rules for assigning an infection event. Those details are not reported in the registry record.
How should a confidence interval be read?
General: A confidence interval communicates the uncertainty around an estimated quantity under the statistical method used. A narrower interval indicates greater precision on that scale, while a wider interval indicates less precision. The interval does not guarantee that the true effect lies within its limits, and it does not measure the probability that a treatment is beneficial. In this trial record, 95% confidence interval is named as the dispersion measure for the primary endpoint, but the interval values are not reported. The precision of the estimate therefore cannot be evaluated from the reported details.
What can the planning assumptions establish?
The record describes a planning illustration based on the observed effect, using a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. It states that the effect to detect is a stated fraction of the observed effect. For time-to-event calculations, the illustration is described as using the total number of events with the Schoenfeld method; other illustrations are described in participants per arm. These are planning assumptions, not evidence about the trial’s original design rationale. The trial’s own sample-size justification is not reported in the registry record.
General: A planning calculation asks how much information a future study might need under chosen assumptions. It is not an observed result and does not show the probability that the completed trial detected an effect. The record does not report the numerical planning illustrations in the information available for this analysis. No planning quantity should be interpreted as observed power or as a trial outcome.
Why do outcome counts and analyses matter?
The registry lists seven outcome measures and zero analyses. General: When several outcomes, time points, or comparisons are examined, the chance of at least one apparently unusual finding can increase if each is interpreted independently. Multiplicity procedures may be used to control a specified error rate, but which procedure is appropriate depends on the analysis plan and scientific goals. The registry record does not report a multiplicity strategy, a statistical analysis plan, or interim analyses. The primary endpoint description says its several categories or time points were not reduced to a single comparison, so no one contrast can be selected from the record as a definitive summary.
General: Over-dispersion occurs when variation in the data is greater than assumed by a model. If ignored, uncertainty estimates can be too small and inferential conclusions too confident. The listed primary endpoint is a time-to-event measure, but the registry entries do not identify an over-dispersion assessment or a model beyond the Kaplan-Meier estimate. There is no basis in the record to assert that over-dispersion was present or that a particular adjustment was used.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists seven outcome measures and zero analyses. Its named secondary outcomes cover changes in CD4 T Cell Count in volunteers who developed HIV infection during the trial for the MITT population, safety assessment of serious adverse events and adverse events, and change in HIV risk behaviors associated with participation for the MITT population. The available record does not include numerical results for these outcomes in the registry record.
Multiplicity concerns can arise when investigators assess several outcomes, time points, or group comparisons. General: If many statistical tests are interpreted without a planned strategy, chance findings can become more likely across the set of tests. Adjustment is not automatic, and the choice depends on which outcomes are confirmatory and how the analysis plan defines the family of comparisons. The registry record does not report a multiplicity adjustment or a statistical analysis plan. It also notes that the primary outcome has several categories or time points and is not reduced to one comparison. A single primary estimate therefore cannot be extracted from the reported information.
The primary population description is modified intent-to-treat and includes participants who were infection-free at entry. The measure title instead says intent to treat. This terminology difference is recorded without assuming how the analysis population was operationalized beyond the description given. Missing-data methods, censoring rules, treatment of participants with incomplete follow-up, and reasons for exclusions are not reported in the registry record. Interim analyses and stopping rules are also not reported in 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 |
|---|---|---|---|
| Vaccine | 1175 | 8197 | 14.3% |
| Placebo | 1219 | 8198 | 14.9% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Vaccine | 85 of 8197 |
| Placebo | 75 of 8198 |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 3.3% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Vaccine | 7442 of 8197 |
| Placebo | 6141 of 8198 |
Most frequent serious adverse event terms
| Event term | Organ system | Vaccine | Placebo |
|---|---|---|---|
| Road traffic accident | Injury, poisoning and procedural complications | 322 of 8197 | 318 of 8198 |
| Abortion spontaneous | Pregnancy, puerperium and perinatal conditions | 73 of 8197 | 54 of 8198 |
| Appendicitis | Infections and infestations | 54 of 8197 | 61 of 8198 |
| Dengue fever | Infections and infestations | 57 of 8197 | 45 of 8198 |
| Suicide attempt | Psychiatric disorders | 24 of 8197 | 23 of 8198 |
| Accident | Injury, poisoning and procedural complications | 24 of 8197 | 22 of 8198 |
| Pharyngitis | Infections and infestations | 24 of 8197 | 20 of 8198 |
| Gastroenteritis | Infections and infestations | 19 of 8197 | 22 of 8198 |
| Gun shot wound | Injury, poisoning and procedural complications | 20 of 8197 | 21 of 8198 |
| Pyelonephritis acute | Infections and infestations | 14 of 8197 | 26 of 8198 |
Most frequent non-serious adverse event terms
| Event term | Organ system | Vaccine | Placebo |
|---|---|---|---|
| Pain/Tenderness | General disorders | 6852 of 8197 | 3727 of 8198 |
| Fatigue | General disorders | 5182 of 8197 | 3410 of 8198 |
| Arm Movement Limitation | General disorders | 5647 of 8197 | 2129 of 8198 |
| Myalgia | General disorders | 4237 of 8197 | 2494 of 8198 |
| Pain/Tenderness | General disorders | 3543 of 8197 | 2991 of 8198 |
| Headache | General disorders | 3677 of 8197 | 2522 of 8198 |
| Arm Movement Limitation | General disorders | 2627 of 8197 | 1943 of 8198 |
| Arthralgia | General disorders | 2177 of 8197 | 1246 of 8198 |
| Swelling | General disorders | 2325 of 8197 | 432 of 8198 |
| Oral Temperature | General disorders | 1564 of 8197 | 1009 of 8198 |
Serious events with the highest arm-level rate: road traffic accident (3.9%), abortion spontaneous (0.9%), appendicitis (0.7%), dengue fever (0.7%), pyelonephritis acute (0.3%).
The registry lists Vaccine and Placebo groups with 8197 and 8198 participants at risk, respectively, for both serious events and other events. The corresponding serious-event affected counts are 1175 and 1219; the other-event affected counts are 7442 and 6141. Deaths are listed as 85 for Vaccine and 75 for Placebo. These are registry-posted counts, not adjusted comparisons. The record does not specify in the available information whether the affected counts represent participants with at least one event or another counting convention, nor does it provide event timing or exposure-adjusted rates.
The listed serious-event terms include Road traffic accident at 3.9%, Abortion spontaneous at 0.9%, Appendicitis at 0.7%, Dengue fever at 0.7%, Pyelonephritis acute at 0.3%, and Pharyngitis at 0.3%. The denominator and group-specific breakdown for these percentages are not reported in the registry record. The listed terms should not be treated as evidence that an event was caused by a study intervention. Counts alone do not account for follow-up duration, chance variation, or differences in exposure. The record’s summary figures therefore describe reported safety data but do not establish a comparative safety effect.
12. What the Result Does, and Does Not, Mean
The posted information documents a randomized, triple-masked trial designed to compare a vaccine regimen with placebos in HIV-uninfected Thai adults. Its primary endpoint was a Kaplan-Meier estimate of HIV-1 infection rate over 42 Months, with a 95% confidence interval identified as the dispersion measure. The endpoint’s infection definition and the intended population are described, and the record reports selected safety counts.
What the record does not provide is the numerical primary endpoint estimate for either group, its confidence limits, or a numerical between-group contrast. Without those values, it is not possible to describe the observed size or precision of the infection-rate comparison. The registry’s statement of purpose is a research question, not a result. Likewise, enrollment and adverse-event counts cannot be used to infer the primary endpoint finding.
General: Statistical evidence is most informative when an estimate is interpreted together with its uncertainty, its population, endpoint definition, and analysis choices. A point estimate alone would not establish certainty, and a confidence interval alone would not resolve limitations in study design or outcome ascertainment. Here, the primary estimate and interval limits are not reported in the registry record, and details of the analysis plan and missing-data handling are also absent.
The safety counts and listed serious-event terms can be read as descriptive registry entries. They do not, by themselves, show that either regimen caused or prevented an event, and the term percentages lack a reported denominator in the record. The deaths are listed as counts without a reported comparative analysis.
Therefore, the defensible interpretation is bounded: the registry identifies what the study set out to measure and provides selected counts, but the available information does not support a quantitative conclusion about the primary infection endpoint. This is a statement about the contents of the registry record, not a claim about findings that may have been reported elsewhere.
13. Why This Trial Matters Statistically
This trial is statistically notable as a large randomized, triple-masked, parallel-group evaluation of a vaccine regimen, with 16402 participants listed as enrolled. Its primary question concerns HIV-1 infection over time, rather than a single measurement taken at one visit. That makes the endpoint definition, follow-up, censoring, and analysis population central to interpreting any estimate.
The registry identifies Kaplan-Meier estimation and a 95% confidence interval, which signals a time-to-event framework and an intention to express uncertainty. At the same time, the registry record does not provide the endpoint estimates or interval limits. This contrast illustrates an important reporting principle: naming a statistical method is not enough to make a result interpretable. Readers also need the numerical estimates, the comparison being made, and enough information about follow-up and analysis choices to understand the evidence.
The record also lists seven outcome measures and zero analyses, and notes that the primary endpoint was not reduced to a single comparison. These details make clear why outcome definitions and multiplicity planning matter. A trial with several outcomes or time points needs a transparent account of which comparisons are central and how uncertainty is handled across them.
Finally, the safety record illustrates the distinction between descriptive counts and comparative inference. Counts and percentages can help characterize reported events, but interpretation depends on denominators, follow-up, event definitions, and a stated analysis. Statistical importance lies not only in the trial’s design, but also in recognizing which conclusions the registry data can and cannot support.
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 most important limitation for interpreting efficacy is that arm-specific primary endpoint estimates and confidence interval limits are not reported in the registry record. The endpoint description supplies a definition and time frame, but no numerical result. The record also states that the primary outcome has several categories or time points and is not reduced to one comparison, preventing a single contrast from being identified.
The primary measure title refers to an intent-to-treat population, while its population description specifies modified intent-to-treat participants who were infection-free at entry. The record does not explain this difference in terminology or report the number included in that population. Follow-up completeness, censoring, infection event counts, missing-data handling, and exclusions are not reported in the registry record.
Methodological details that would aid assessment are also not reported: randomization sequence and concealment procedures, which roles were masked, the detailed HIV diagnostic algorithm, and the statistical analysis plan. The record does not report interim analyses, stopping rules, or a multiplicity strategy. The trial’s own sample-size justification is not reported in the registry record.
Safety interpretation is limited by the absence of group-specific serious-event term counts, an identified denominator for the listed percentages, and details on event counting and follow-up. The reported group counts should not be treated as directly comparable rates. These limitations restrict conclusions from the registry record; they do not establish what results may appear in other reports.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: HIV Vaccine Trial in Thai Adults — NCT00223080.
- Registry record last updated 2019-04-24; status last verified 2019-04.
- Results first posted 2018-10-19.
- 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
The record describes a completed Phase III randomized, triple-masked, parallel-group trial sponsored by the U.S. Army Medical Research and Development Command. Enrollment was 16402; the study began in 2003-10 and reached primary completion in 2006-07. The intervention was ALVAC-HIV vCP1521 plus AIDSVAX, compared with ALVAC and AIDSVAX placebos.
The primary measure was a Kaplan-Meier estimate of HIV-1 infection rate over 42 Months in participants described as infection-free at entry. Infection detection used a diagnostic algorithm involving serologic and nucleic acid technologies. Seven outcome measures and zero analyses are listed. The record contains selected safety counts and serious-event terms, but does not report numerical arm-specific primary endpoint estimates or confidence interval limits. The analysis population description, missing-data methods, multiplicity strategy, and detailed statistical plan are not fully reported in the registry record.