Safety and Immunogenicity of HIV-1 Vaccines C62-M4 or C1C62-M3M4 in Persons With HIV-1 Suppressed on ART: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Safety and Immunogenicity of HIV-1 Vaccines C62-M4 or C1C62-M3M4 in Persons With HIV-1 Suppressed on ART (NCT05604209), a randomized phase 1 study. The primary outcome is Percent of Participants With a Grade 3 or Higher Treatment-Related Adverse Event (AE).

2. Clinical Question

3. Trial Design

This was a randomized, parallel-group phase I study sponsored by the University of North Carolina, Chapel Hill. It compared C62-M4 and C1C62-M3M4 with placebo in people with HIV-1 suppressed on antiretroviral therapy. The registry record lists the study as completed, with enrollment of 18. The recorded study start was 2022-10-13, and primary completion was 2024-09-12.

The treatment sequences distinguish the experimental arms by the vaccine components administered at each visit. C62-M4 consisted of ChAdOx1.HIVconsv62 on Day 0 and MVA.tHIVconsv4 on Day 28. C1C62-M3M4 consisted of ChAdOx1.tHIVconsv1 and ChAdOx1.HIVconsv62 on Day 0, then MVA.tHIVconsv3 and MVA.tHIVconsv4 on Day 28. Placebo was administered on both days. The registry classifies masking as triple; its brief description also calls the study double blind. Further detail about who was masked is not reported in the registry record.

The primary safety observation period ran from the first day of study treatment through 28 days following the last vaccination, described as an average of 2 months. The primary endpoint counted participants with a treatment-related adverse event graded 3 or higher. Relatedness included events judged possible, probable, or definite according to the protocol. The registry also lists immune-response outcomes, including fold-change in T-cell response to HIV-1 mosaic immunogens and change in breadth of responses targeting conserved immunogen subpools. Results for those secondary outcomes are not included in the posted primary endpoint figures described in the record.

The registry does not report details of the randomization sequence, allocation concealment, or the reasons for the enrollment target. It also does not report a statistical analysis plan or the role of any interim analyses.

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: All participants that received C62-M4, C1C62-M3M4, or placebo were included.

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: Includes participants that were randomized to one of three study arms.

6. Primary Endpoint

The registry lists the primary outcome as Percent of Participants With a Grade 3 or Higher Treatment-Related Adverse Event (AE), measured over First day of study treatment through 28 days following last vaccination, an average of 2 months.

The primary endpoint is the percentage of participants with a treatment-related adverse event graded 3 or higher. The grading system is the DAIDS Table for Grading the Severity of Adult and Pediatric Adverse Events, corrected Version 2.1, July 2017. In that system, Grade 3 is severe and Grade 4 is potentially life-threatening. An event counted as treatment-related if the assessment was possible, probable, or definite relatedness as defined in the protocol.

This endpoint is used to describe an important aspect of safety: the frequency of more severe events considered related to study product during the specified observation period. Reporting a percentage makes the event frequency interpretable relative to the number of participants in each arm. The accompanying confidence interval communicates uncertainty around that percentage, which is especially important when groups are small. It does not establish that an event was caused by a vaccine, nor does it capture every dimension of safety. The registry also lists a secondary endpoint for participants with a Grade 1 or higher treatment-related adverse event, but the primary results focus on Grade 3 or higher events.

The observation period extended from the first day of study treatment through 28 days following the last vaccination, an average of 2 months. The primary population is described as all participants who received C62-M4, C1C62-M3M4, or placebo. The registry record does not provide additional detail about handling incomplete follow-up or missing endpoint data.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary endpoint is binary at the participant level: a participant either had or did not have a treatment-related adverse event graded 3 or higher during the specified observation period. The reported measure is the percentage of participants with such an event in each arm. This describes event frequency within each group; it is not itself a measure of the difference between groups.

What does the confidence interval express?

In general, a confidence interval describes statistical uncertainty around an estimate. Repeated use of a specified interval procedure would produce intervals that cover the underlying quantity at the stated confidence level at the stated rate, under the method's assumptions. It is not a guarantee that the particular interval contains the true value, nor does it say that values inside the interval are equally plausible. A confidence interval for each arm's percentage also does not directly test whether arms differ.

The registry reports 95% confidence intervals estimated with the Clopper-Pearson exact method. In general, exact binomial intervals are based on the binomial model and are often used for event proportions when group sizes or event counts are small. They can be conservative, meaning their actual coverage may exceed the nominal confidence level. The reported interval widths are substantial, illustrating that these arm-specific percentages are not estimated precisely. For C62-M4, the point estimate is 12.5% and the interval is 0.32% to 52.7%. For C1C62-M3M4, the point estimate is 0.0% and the interval is 0.0% to 36.9%. For placebo, the point estimate is 0.0% and the interval is 0.0% to 84.2%.

Why is a zero estimate not proof of zero risk?

In general, when no events are observed in a group, the estimated percentage is zero, but uncertainty remains about the underlying event probability. The width of an interval depends on the amount of information in the data. With limited group sizes, a zero observed percentage can coexist with an upper confidence bound that is appreciably above zero. Thus, the 0.0% point estimates in the C1C62-M3M4 and placebo arms should be read together with their confidence intervals, not as proof that events cannot occur.

Why is there no arm-to-arm conclusion?

A comparison requires an estimable contrast between groups, such as a difference in percentages, together with uncertainty for that contrast. The registry record marks values as missing or not estimable for a two-arm comparison of this binary endpoint. Accordingly, the arm-specific results do not support a reported inferential comparison. No comparative estimate or p-value is reported in the registry record. In general, overlapping or non-overlapping arm-specific confidence intervals are not a replacement for a properly calculated comparison; the uncertainty of the contrast must be assessed directly.

The analysis population is described as all participants who received C62-M4, C1C62-M3M4, or placebo. The posted arm results give group sizes of 8, 8, and 2. The registry does not explain whether participants were excluded from these summaries, how incomplete observations were handled, or whether the analysis followed an intention-to-treat principle. Those details are not reported in the registry record.

What does the planning illustration represent?

In general, sample-size planning asks how many participants would be needed to detect a specified effect under stated assumptions. A planning illustration based on an observed effect is not a measure of the trial's observed power and is not a substitute for the trial's original design justification. The registry describes planning assumptions of a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation, with the effect to detect specified as a fraction of the observed effect. The record does not report the trial's own sample-size justification. For this binary endpoint, the record indicates that a two-arm comparison is not estimable, so a comparison-based planning result is not available from the posted results.

In general, over-dispersion matters when data vary more than an assumed model allows, because standard errors can then be too small and confidence intervals too narrow. The primary endpoint is a binary participant-level outcome, and the registry reports an exact binomial interval rather than a model that assumes a continuous outcome with constant variance. No over-dispersion adjustment or separate model-based analysis is reported in the registry record. The record also does not report details of model diagnostics, sensitivity analyses, or adjustments for covariates.

The registry lists 17 analyses and 7 outcome measures, but those counts do not explain which statistical procedures were used for every outcome or how results were selected for reporting. The methods apply to the stated primary safety endpoint; they should not be assumed to describe the analysis of immune-response outcomes.

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("C62-M4", "C1C62-M3M4", "Placebo")
n      <- c(8, 8, 2)
events <- c(1, 0, 0)
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  C62-M4  8  1  12.5  0.3  52.7  2.2  47.1  2.8  48.2
ARM  C1C62-M3M4  8  0  0.0  0.0  36.9  0.0  32.4  0.3  33.6
ARM  Placebo  2  0  0.0  0.0  84.2  0.0  65.8  0.8  70.8

11. Multiplicity, Missing Data and Analysis Populations

The registry lists a primary safety outcome and secondary outcomes covering treatment-related adverse events, T-cell response magnitude to HIV-1 mosaic immunogens, and breadth of responses targeting conserved HIV-1 immunogen subpools. It reports 6 secondary outcomes and 17 analyses. The registry record does not report whether the analysis plan adjusted for testing multiple outcomes or comparisons, or whether any outcome hierarchy was used beyond identifying the primary endpoint.

In general, testing many hypotheses can increase the chance of obtaining at least one apparently notable result by chance. Methods such as adjusted significance thresholds or hierarchical testing can address that issue, but whether any such method was planned or used is not reported in the registry record. The count of analyses alone does not establish that multiplicity was or was not controlled. The posted primary safety percentages are descriptive arm-specific results, and the record does not provide an estimable two-arm comparison for this binary endpoint.

The primary population is stated to include participants who received one of the study regimens or placebo. Group sizes are reported for the primary outcome. Further information about missing endpoint observations, withdrawals, exclusions, or imputation is not reported in the registry record. It is also not reported whether participants were analyzed according to assignment, treatment received, or another population definition for the secondary outcomes.

These gaps limit assessment of how missing information and multiple analyses may affect interpretation. They do not change the reported arm-specific percentages, but they leave uncertainty about the complete analysis strategy and the extent to which the posted results represent all planned analyses.

12. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

Most frequent non-serious adverse event terms

The serious adverse event figures report zero serious events in each arm: C62-M4 had 0 among 8 at risk, C1C62-M3M4 had 0 among 8 at risk, and placebo had 0 among 2 at risk. The record also reports 0 deaths in each arm. These counts are distinct from the primary endpoint, which concerns treatment-related events graded 3 or higher; the registry's serious-event summaries do not, by themselves, identify all events meeting that primary definition.

In general, observing no serious events in a group does not establish that the risk is zero. The amount of uncertainty depends on the number of people observed and the duration and completeness of follow-up. The placebo group is especially limited in size, and the absence of observed serious events there cannot support a precise estimate of a rare event frequency. The registry does not provide confidence intervals for these serious-event counts.

The record lists other adverse events affecting all participants at risk in each arm. That is a broader category than serious adverse events and should not be read as meaning that all such events were severe or treatment-related. The registry record does not provide terms for serious events because none are listed among the top serious terms. These safety summaries describe observed events during the reported study period; they do not establish comparative safety or characterize risks beyond the study's observation window.

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

The primary results describe the observed frequency of treatment-related adverse events graded 3 or higher in each study arm during the stated safety observation period. The registry reports 12.5% for C62-M4, 0.0% for C1C62-M3M4, and 0.0% for placebo, with broad 95% confidence intervals. The registry record also reports no serious adverse events and no deaths in the arm-specific safety summaries.

These findings do not establish that one regimen is safer than another. The record says that a two-arm comparison for the binary primary endpoint is missing or not estimable, and the small group sizes leave the arm-specific estimates imprecise. A point estimate of 0.0% is an observed result, not proof of no underlying risk. Nor does the C62-M4 point estimate alone establish a difference from the other arms.

The results also do not answer whether the vaccines improve immune responses or help the body get rid of HIV in cells. Those aims appear in the trial description, and the registry lists secondary T-cell response outcomes, but their results are not reported in the primary safety results. The safety endpoint is not an efficacy endpoint, and it does not assess the full range of clinical outcomes.

In general, a phase I study can provide early descriptive information about safety and immune-response measures in its studied population. Conclusions are bounded by the enrolled participants, observed follow-up, outcome definitions, and available analyses. The registry record does not report enough statistical detail to reconstruct a comparative analysis or evaluate missing-data handling. Accordingly, the posted data support a description of observed event percentages and their uncertainty, not a treatment recommendation, proof of benefit, or definitive assessment of risk.

14. Why This Trial Matters Statistically

This trial is statistically informative because it illustrates the difference between reporting arm-specific event frequencies and estimating a treatment contrast. The primary results give a percentage and confidence interval for each arm, but the registry record does not provide an estimable two-arm comparison. Readers therefore need to distinguish descriptive summaries from evidence about differences between regimens.

The broad confidence intervals make precision central to interpretation. The reported point estimates are not equally informative: uncertainty depends on the amount of observed information in each group, and the placebo arm has a group size of 2. The upper confidence bound for placebo reaches 84.2%, while the reported point estimate is 0.0%. This contrast shows why the interval matters and why a zero observed percentage should not be treated as certainty about the underlying risk.

The trial also makes clear that statistical interpretation depends on the endpoint definition. The primary outcome counts Grade 3 or higher treatment-related adverse events, whereas the registry separately lists a Grade 1 or higher treatment-related adverse event outcome and serious adverse-event summaries. These measures describe different aspects of safety and should not be conflated.

Finally, the record identifies important limits on what can be inferred: it does not report a sample-size justification, a complete statistical analysis plan, multiplicity handling, or missing-data procedures. Such details matter for understanding how analyses were planned and how completely the posted results represent the intended analyses. The record's transparency about the unestimable comparison is itself important: it prevents arm-level percentages from being mistaken for a supported comparative finding.

15. 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 endpoint results are based on small arm-specific groups, including a placebo group of 2. As a result, the confidence intervals are broad and the percentages are imprecise. The registry identifies the two-arm comparison as missing or not estimable, so the posted results do not support a formal comparative conclusion for the primary binary outcome.

The outcome is restricted to treatment-related adverse events graded 3 or higher during the specified observation period. It does not represent every adverse event, every safety domain, or longer-term safety. The record describes the observation period as extending through 28 days following the last vaccination, an average of 2 months. The registry record does not report additional follow-up results or how incomplete observations were handled.

The primary population is described as participants who received a study regimen or placebo, but the registry does not provide further detail on exclusions, withdrawals, or the analysis population for each outcome. The record does not report the original sample-size justification, a full statistical analysis plan, multiplicity procedures, or whether interim analyses occurred. It also does not explain which analyses correspond to the reported count of 17 analyses.

Immune-response outcomes are listed, but their results are not included in the primary safety results described in the registry record. Consequently, the available information cannot support conclusions about the immune-response aims. The study population is limited to people with HIV-1 suppressed on antiretroviral therapy; results should not be generalized beyond that population without additional evidence. These limitations constrain both the precision of the safety estimates and the scope of interpretation.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Safety and Immunogenicity of HIV-1 Vaccines C62-M4 or C1C62-M3M4 in Persons With HIV-1 Suppressed on ART — NCT05604209.
• Registry record last updated 2025-08-24; status last verified 2025-04.
• Results first posted 2025-08-24.
• 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.

19. Record Summary

NCT05604209 is a completed randomized, parallel-group phase I study sponsored by the University of North Carolina, Chapel Hill. It enrolled 18 people with HIV-1 suppressed on antiretroviral therapy and compared C62-M4, C1C62-M3M4, and placebo. The recorded study start was 2022-10-13, and primary completion was 2024-09-12.

The primary endpoint was the percentage of participants with a Grade 3 or higher treatment-related adverse event during the stated observation period. The registry reports arm-specific percentages with Clopper-Pearson 95% confidence intervals, but identifies the two-arm binary comparison as missing or not estimable. Serious adverse event counts and deaths were zero in each arm. Secondary outcomes include T-cell response measures, but their results are not reported in the primary results summarized by the registry.

The registry record does not report a full statistical analysis plan, sample-size justification, multiplicity approach, or detailed missing-data procedures. The posted findings therefore support descriptive interpretation of the primary safety outcome, with substantial uncertainty, rather than a comparative conclusion.