Evaluation of the Efficacy and Safety of VX-864 in Subjects With the PiZZ Genotype: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Evaluation of the Efficacy and Safety of VX-864 in Subjects With the PiZZ Genotype (NCT04474197), a randomized phase 2 study. The primary outcome is Change in Plasma Functional Alpha-1 Antitrypsin (AAT) Levels.

2. Clinical Question

This is a short-term, biomarker-focused question. The primary endpoint concerns a laboratory measure of functional alpha-1 antitrypsin in plasma, rather than a clinical event or a measure of symptoms. The registry also lists change in plasma antigenic alpha-1 antitrypsin levels and observed pre-dose plasma concentration of VX-864 as secondary outcomes. Those measures address different aspects of the study: the antigenic outcome concerns measured protein levels, while the pre-dose concentration is a pharmacokinetic measure.

The registry record does not report a clinical outcome question such as whether treatment changes symptoms, complications, or longer-term health. The posted primary comparisons therefore address the difference in the specified laboratory endpoint at Day 28, not the full range of possible clinical effects.

3. Trial Design

This was a phase 2, randomized, double-blind, placebo-controlled study with a parallel-group design. The registry records quadruple masking. It does not identify in the registry record which specific roles were masked, so the masking label should be read as a registry classification rather than an account of exactly who knew each assignment.

The study included a matched placebo group and VX-864 groups receiving 100 mg, 300 mg, or 500 mg every 12 hours. Treatment was planned for 28 days. The registry lists enrollment as 44 and the status as completed. The recorded study start date is 2020-07-24, and the primary completion date is 2021-05-04. These dates describe the registry record and do not, by themselves, explain the timing of individual assessments or any later follow-up.

Randomization is intended to make treatment groups comparable on average, while masking can reduce the influence of treatment knowledge on participant experience, care, and assessment. These are general purposes of the design; the registry record does not report the randomization procedure or the practical details of masking. Likewise, it does not report the allocation ratio, sequence-generation method, or any stratification factors.

The primary analysis population was the full analysis set, defined in the record as all randomized participants who received at least 1 dose of study drug. This definition excludes randomized participants who did not receive a dose, if any, and the record does not give a separate account of such participants. The arm-level results report the analysis group sizes for the primary endpoint. Those values should not be treated as a substitute for a participant-flow account, which is not reported in the registry record.

The study was sponsored by Vertex Pharmaceuticals Incorporated. The registry describes the objective as evaluating efficacy, safety, and pharmacokinetics of VX-864 in PiZZ subjects. It does not report the protocol’s sample-size justification, a planned interim analysis, or detailed monitoring arrangements.

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: This study was conducted in participants 18 through 80 of years of age, inclusive with the PiZZ genotype.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Full analysis set (FAS) included all randomized participants who received at least 1 dose of study drug.

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.

6. Primary Endpoint

The registry lists the primary outcome as Change in Plasma Functional Alpha-1 Antitrypsin (AAT) Levels, measured over From Baseline at Day 28.

The primary endpoint was change in plasma functional alpha-1 antitrypsin levels from baseline at Day 28, measured in micromoles per liter. The registry reports the group estimates as least-squares means, with standard errors as the dispersion measure. It also reports model-based comparisons of each VX-864 group with placebo.

A functional measure is intended to capture the measured activity of the protein, whereas an antigenic measure concerns the amount detected by an assay. This is a general distinction between functional and antigenic laboratory outcomes; the registry record does not give assay procedures or explain how the measured values map to clinical outcomes. The antigenic alpha-1 antitrypsin outcome is listed as secondary, not as the primary endpoint.

Biomarkers can be useful in early-stage trials because they allow investigators to assess a biological measure over a defined treatment period. In general, a change from baseline describes how the endpoint moves relative to a participant’s starting value, while a comparison with placebo helps distinguish the observed treatment-group pattern from change in the control group. Neither feature alone establishes the importance of a change to patients.

The registry does not report a threshold for a clinically important difference in functional alpha-1 antitrypsin levels. It also does not report the measurement schedule beyond the primary timeframe, From Baseline at Day 28, or details about how baseline values were incorporated into the model.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is continuous: it is a measured laboratory value expressed in micromoles per liter. For continuous outcomes, a group mean or model-based mean summarizes the central tendency of the observations. The registry labels the group estimates as least-squares means, which are model-derived estimates rather than necessarily simple arithmetic averages. Their interpretation depends on the fitted model and the data included in that model.

What does the standard error describe?

The registry reports standard errors alongside the least-squares mean changes. A standard error describes the precision of an estimated mean: in general, smaller standard errors indicate less sampling uncertainty around that estimate, given the analysis and its assumptions. It is not the same as a standard deviation. A standard deviation describes variation among participant measurements, while a standard error describes uncertainty in an estimated quantity. The registry does not report standard deviations for these primary endpoint estimates.

The reported standard errors are 0.3 for placebo, 0.3 for VX-864 100 mg, 0.2 for VX-864 300 mg, and 0.2 for VX-864 500 mg. They should be interpreted as precision measures for the reported group estimates, not as ranges containing a stated proportion of individual participant values. No additional precision measure for the group means is needed to interpret the sponsor-reported contrasts, which have their own confidence intervals.

What does the mixed-effects model contribute?

The registry identifies the comparison method as a mixed-effects model for repeated measures. In general, such a model can account for repeated outcome measurements from the same participant and estimate treatment-group differences using data across assessment times. The model’s name indicates a repeated-measures approach, but the registry record does not report the specific model equation, covariance structure, included covariates, handling of baseline values, or assumptions about missing observations. These details affect how the model’s estimates should be understood and cannot be inferred from the method label alone.

The registry reports the primary timeframe as change from baseline at Day 28, but it does not specify the full set of visits used in the repeated-measures model. It is therefore not possible to reconstruct the fitted analysis from the registry description alone. In general, mixed-effects models can use available repeated measurements without requiring every participant to have a complete set of observations, but that general property does not establish how missing data were handled in this trial.

How should the mean differences be read?

The least-squares mean difference compares the model-based estimate for a VX-864 group with the estimate for placebo. The registry reports differences of 2.3 micromoles per liter for VX-864 100 mg, 2.3 for VX-864 300 mg, and 2.2 for VX-864 500 mg. A positive difference means the estimated change was higher in the named VX-864 group than in placebo on the reported scale. This is a description of the contrast, not a judgment about clinical benefit.

Each difference is accompanied by a 95% confidence interval. In general, a confidence interval reflects uncertainty in an estimate under the model and its assumptions. Its endpoints are not a guarantee that the true value falls inside the interval, and a confidence interval does not show the range of participant-level responses. The intervals are 1.5 to 3.1 for VX-864 100 mg, 1.6 to 3.1 for VX-864 300 mg, and 1.5 to 2.9 for VX-864 500 mg.

What do the p-values indicate?

The reported p-values are p < 0.001 for all three comparisons. In general, a p-value measures how incompatible the observed data are with a specified null hypothesis, under the assumptions of the statistical model. It is not the probability that the null hypothesis is true, nor is it a measure of effect size or clinical importance. The registry labels the comparisons as superiority analyses. The very small reported p-values indicate strong statistical evidence against a zero-difference null in each listed model comparison, while leaving clinical relevance and broader generalizability as separate questions.

The three contrasts share the placebo group. In general, multiple comparisons can increase the chance of at least one false-positive result if a family of tests is interpreted without an appropriate multiplicity strategy. Whether and how multiplicity was controlled is not reported in the registry record. The reported p-values should therefore be read as the values attached to the listed sponsor analyses, without assuming a particular adjustment that the record does not describe.

Simple unadjusted re-calculations from posted summary statistics, when available, answer a different question from the sponsor’s mixed-effects model. Such calculations do not reproduce the repeated-measures model or any adjustments it used. The registry’s reported model-based estimates and inferential results are the appropriate figures for describing the sponsor analysis; the record flags no discrepancy between that analysis and the recalculation.

Finally, the design and the model do not remove uncertainty about measurement quality, missing data, or unreported analysis choices. The registry record does not provide enough detail to assess all model assumptions or independently reproduce the reported analysis.

10. Confidence Intervals for Each Arm

No two-arm comparison is shown for this trial, but each arm's mean can be given with a t-based 95% confidence interval computed from the posted mean, spread and number of participants.

R code and output

arm <- c("Placebo", "VX-864 100 mg", "VX-864 300 mg", "VX-864 500 mg")
n   <- c(7, 10, 9, 18)
m   <- c(-0.1, 2.3, 2.3, 2.1)
sp  <- c(0.3, 0.3, 0.2, 0.2)
sd  <- sp * sqrt(n)      # standard errors converted to SDs
for (i in seq_along(n)) {
  se <- sd[i] / sqrt(n[i]); h <- qt(0.975, n[i] - 1) * se
  cat(sprintf("CARM|%s|%d|%.3f|%.3f|%.3f|%.3f\n", arm[i], n[i], m[i], sd[i], m[i] - h, m[i] + h))
}

CARM  Placebo  7  -0.100  0.794  -0.834  0.634
CARM  VX-864 100 mg  10  2.300  0.949  1.621  2.979
CARM  VX-864 300 mg  9  2.300  0.600  1.839  2.761
CARM  VX-864 500 mg  18  2.100  0.849  1.678  2.522

11. Analyses Reported by the Sponsor

The registry reports the sponsor’s primary comparisons using a mixed-effects model for repeated measures. These are adjusted, model-based least-squares mean differences, with 95% confidence intervals and p-values. The reported contrasts are 2.3 micromoles per liter for VX-864 100 mg versus placebo, 2.3 for VX-864 300 mg versus placebo, and 2.2 for VX-864 500 mg versus placebo. Each is reported with p < 0.001.

A simple recalculation from posted summary statistics is unadjusted and cannot reproduce the repeated-measures model. It may be useful as a check on the broad direction or scale of the contrast, but it does not replace the sponsor’s analysis or its stated inferential method. The registry does not flag a discrepancy between the sponsor-reported results and the recalculation.

In general, the sponsor’s analysis takes precedence when a discrepancy is flagged, because it is the reported analysis planned or conducted for the trial rather than a simplified calculation from summary values. That issue is not flagged in this record. The registry does not provide sufficient model specification to independently reproduce the mixed-effects analysis in full, and it does not report the protocol-level analysis plan.

12. Multiplicity, Missing Data and Analysis Populations

The registry lists 4 outcome measures and 6 analyses. It identifies the primary endpoint as change in plasma functional alpha-1 antitrypsin levels and lists two secondary outcomes: change in plasma antigenic alpha-1 antitrypsin levels and observed pre-dose plasma concentration of VX-864. The posted primary results include comparisons of each VX-864 dose with placebo.

When several outcomes, doses, or time points are tested, the interpretation of individual p-values can depend on whether the analyses were treated as a family and whether multiplicity was addressed. In general, adjustments can be used to limit the chance of false-positive findings across a set of tests. The registry record does not report whether a multiplicity adjustment was planned or used, how any family of tests was defined, or whether the listed comparisons were confirmatory or exploratory. The reported p-values should therefore be understood as the values attached to the posted comparisons, without assuming an unreported correction.

The analysis population is specified as the full analysis set, including all randomized participants who received at least 1 dose of study drug. The endpoint group sizes are reported as 7 for placebo, 10 for VX-864 100 mg, 9 for VX-864 300 mg, and 18 for VX-864 500 mg. The registry does not provide a detailed participant-flow account or explain whether any randomized participants were excluded from this analysis population.

Although the primary method is described as a mixed-effects model for repeated measures, specific missing-data procedures and assumptions are not reported in the registry record. The model label alone does not reveal whether data were missing, why they were missing, or how missingness was assessed. The record also does not report a sensitivity analysis for missing data, a protocol-level statistical analysis plan, or the handling of protocol deviations. An interim analysis is not reported in the registry record.

13. 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 5% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: chest pain (5.6%), pneumothorax spontaneous (5.6%).

The registry reports serious adverse events for the placebo group and each VX-864 dose group. The recorded counts were 0 among 7 participants in the placebo group, 0 among 10 in the VX-864 100 mg group, 0 among 9 in the VX-864 300 mg group, and 2 among 18 in the VX-864 500 mg group. These are counts of participants recorded as affected, not estimates of comparative risk. No deaths were reported in any group.

Other adverse events were recorded in 4 of 7 participants receiving placebo, 7 of 10 receiving VX-864 100 mg, 7 of 9 receiving VX-864 300 mg, and 17 of 18 receiving VX-864 500 mg. These counts are separate from the serious adverse event counts and should not be combined with them. The registry lists chest pain and spontaneous pneumothorax among the top serious adverse event terms, each at 5.6%. The record does not specify the group assignment for those terms in that listing.

Safety counts in a trial of this size and short treatment duration are descriptive. They do not, on their own, establish whether an event was caused by treatment or allow a precise comparison of uncommon harms. The registry record does not provide event-level narratives or a fuller account of severity, timing, relatedness, or duration.

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

The posted primary results show higher model-based changes in functional alpha-1 antitrypsin levels in each VX-864 group than in the placebo group at Day 28. The sponsor-reported mean differences are positive, their 95% confidence intervals lie above zero, and the reported p-values are p < 0.001 for all three comparisons. These findings describe the specific laboratory endpoint, treatment period, analysis population, and statistical model recorded for the study.

They do not establish that a laboratory change is clinically important. The registry does not report a threshold for clinical importance, nor does it link the primary endpoint to a patient-centered outcome. The primary result therefore cannot be read as evidence about symptoms, longer-term health, or clinical events that are not reported as outcomes in this record.

The results also do not establish the relative merits of the VX-864 doses. The posted inferential comparisons are each against placebo; direct statistical comparisons among the VX-864 groups are not reported in the registry record. Close point estimates are not proof of equivalent effects, and separate comparisons against a shared control do not answer whether one dose differs from another.

The duration of treatment was 28 days, and the primary outcome timeframe was Day 28. The registry record does not report whether the measured changes persisted after treatment, whether there were later outcomes, or how the laboratory findings relate to longer-term effects. The results should not be extended beyond the recorded population and study conditions without additional evidence.

Statistical significance and clinical importance are distinct. In general, a small p-value indicates that the observed data are difficult to reconcile with a null hypothesis under the analysis assumptions; it does not measure the size or importance of an effect. The confidence intervals convey uncertainty about the model-based differences, but they do not resolve questions about clinical meaning, external validity, or unreported analysis details.

15. Why This Trial Matters Statistically

This trial illustrates how an early-stage randomized study can frame a primary question around a continuous biomarker rather than a clinical event. The primary outcome is change in functional alpha-1 antitrypsin levels, and the registry reports group-level least-squares means, standard errors, and model-based comparisons with placebo. Reading these quantities together helps distinguish the estimated changes within groups from the estimated differences between groups.

The study also shows why the analysis method matters. A mixed-effects model for repeated measures is not interchangeable with a simple comparison of endpoint summaries. In general, repeated-measures models can use information across scheduled assessments and account for within-participant correlation. The registry identifies the model class, but not enough detail to reconstruct its exact specification. That distinction is important when comparing sponsor-reported inference with an unadjusted recalculation.

The three dose-versus-placebo comparisons are statistically clear in the posted results, while several broader questions remain open. The registry does not report a multiplicity strategy, a direct comparison among dose groups, a clinical-importance threshold, or the relationship between the biomarker and patient-centered outcomes. Those omissions limit what can be inferred from small p-values alone.

The safety counts also illustrate the limits of descriptive evidence in a relatively small, short-duration study. Counts can identify events recorded during the trial, but they cannot by themselves settle causation or provide precise estimates for uncommon events. Statistical interpretation therefore depends not only on the apparent strength of a result, but also on the outcome chosen, the analysis method, the reporting detail, and the scope of the study.

16. 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 registry record does not provide the full statistical analysis plan or enough detail to reproduce the mixed-effects model for repeated measures. The model’s covariance structure, included covariates, baseline handling, and assumptions about missing observations are not reported. These omissions make it difficult to independently assess how the reported estimates would change under alternative reasonable model specifications.

The primary endpoint is measured at Day 28 after a 28-day treatment period. The record does not report longer-term primary endpoint follow-up, so persistence of the observed biomarker differences cannot be assessed from these results. It also does not report a threshold for a clinically important difference or establish how the biomarker relates to clinical outcomes.

The analysis population definition is stated, but a participant-flow account and reasons for exclusions or missing outcome data are not reported in the registry record. The absence of those details limits assessment of whether the analysis population differed from the randomized population in a way that could affect interpretation. Missing-data procedures and sensitivity analyses are also not reported.

The registry posts comparisons of each VX-864 dose with placebo, but direct comparisons among dose groups are not reported. A dose pattern should not be inferred as a formal dose-response result from these separate control comparisons. The multiplicity strategy is not reported, so it is not possible to determine from the record whether or how the set of outcome and dose comparisons was controlled for multiple testing.

The safety results are counts from a short study, and the registry does not provide detailed event narratives, timing, severity, or relatedness. The top serious adverse event terms are listed with percentages, but their treatment-group assignments are not specified in that listing. These limitations constrain interpretation of the safety summary as well as the primary efficacy endpoint.

17. Related Tutorials

18. Related Statistical Calculators

19. Sources

• ClinicalTrials.gov: Evaluation of the Efficacy and Safety of VX-864 in Subjects With the PiZZ Genotype — NCT04474197.
• Registry record last updated 2022-05-26; status last verified 2022-05.
• Results first posted 2022-05-26.
• 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.

20. Record Summary

NCT04474197 is a completed phase 2 randomized, double-blind, placebo-controlled, parallel-group study sponsored by Vertex Pharmaceuticals Incorporated. It enrolled 44 participants with alpha-1 antitrypsin deficiency and the PiZZ genotype. The recorded study dates are 2020-07-24 and 2021-05-04 for study start and primary completion.

Participants received matched placebo or VX-864 at 100 mg, 300 mg, or 500 mg every 12 hours for 28 days. The primary endpoint was change from baseline at Day 28 in plasma functional alpha-1 antitrypsin levels. The sponsor-reported mixed-effects model for repeated measures comparisons against placebo had positive least-squares mean differences for all three dose groups, with p < 0.001 in each comparison.

The registry also lists antigenic alpha-1 antitrypsin change and pre-dose VX-864 concentration as secondary outcomes. Important details not reported in the registry record include the full model specification, missing-data procedures, multiplicity strategy, and the clinical-importance threshold for the primary biomarker.