Maribavir vs. Valganciclovir for CMV Prophylaxis in High-Risk Kidney Transplant Recipients: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Maribavir vs. Valganciclovir for CMV Prophylaxis in High-Risk Kidney Transplant Recipients (NCT06034925), a randomized phase 4 study. The primary outcome is Clinical Significant Leukopenia.

2. Clinical Question

The trial’s stated purpose includes assessing tolerability as well as CMV prevention. The posted primary result described in the registry record is about leukopenia, a blood-cell outcome; it is not itself a result about CMV infection. The record lists two outcome measures, but only the primary endpoint is described in detail in the posted results used for this comparison. No secondary outcome results are posted.

The central statistical contrast is the difference in observed leukopenia proportions between the maribavir and valganciclovir groups. The comparison is based on participants assigned to the two regimens, rather than on a reported time-to-event measure. The registry describes the endpoint as a count of participants with the event, and its timeframe is one year following transplant.

3. Trial Design

This is a phase 4 randomized controlled trial with a parallel-group design. The registry lists 70 participants as the enrollment. The posted primary outcome counts show 35 participants in the control group and 35 in the intervention group. The control is valganciclovir and the intervention is maribavir.

The trial is listed as completed. Its recorded start date is 2023-11-06, and its primary completion date is 2025-06-30. The sponsor is Medical University of South Carolina. The record lists transplant complication and CMV among the conditions relevant to the study.

Masking is listed as none, so this is an open-label comparison in the registry record. The record does not describe further details about who knew treatment assignment, how assignment was concealed, or how endpoint assessment was conducted. Those details are not reported in the registry record and should not be inferred from the open-label designation alone.

The arm descriptions specify valganciclovir 900mg once daily and maribavir 400mg twice daily. The brief summary describes the maribavir regimen as maribavir plus acyclovir, whereas the arm description names maribavir without listing acyclovir. The record’s description of the maribavir regimen is therefore not fully consistent across these summaries; additional administration details are not reported in the registry record.

The primary endpoint is clinically significant leukopenia during one year following transplant. The posted group counts are 8 of 35 participants in the valganciclovir group and 1 of 35 in the maribavir group. The registry record does not report the trial’s original sample-size justification, detailed statistical analysis plan, or any interim-analysis plan.

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

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 Clinical Significant Leukopenia, measured over One year following transplant.

The primary endpoint counts participants who develop clinically significant leukopenia during one year following transplant. The registry definition requires both a white blood cell count <3,000 cells/mm3 and an adjustment in either mycophenolate or the antiviral prophylaxis. It is therefore a defined clinical event combining a laboratory threshold with a treatment adjustment, rather than a count of every low white blood cell result regardless of whether management changed.

The posted outcome is binary at the participant level: each participant either met the endpoint definition or did not. The registry lists the unit as participants and the outcome type as a count of participants with an event. This makes a comparison of the proportions affected in the two randomized groups a natural way to describe the result.

As a tolerability measure, clinically significant leukopenia captures a blood-cell outcome that was important enough, under the registry definition, to prompt an adjustment in immunosuppressive or antiviral treatment. It is distinct from the study’s CMV-prevention objective: this endpoint does not directly count CMV infections. The registry record does not report further details about the timing of blood-count assessments, the specific adjustment rules, or how events were adjudicated.

For interpretation, the endpoint’s definition matters. The result concerns events meeting both parts of the definition, not leukopenia alone, and it does not describe the severity or duration of each event. The registry record does not report those additional characteristics.

7. Results Posted in the Registry

• Intervention: 2.9% (1/35) versus 22.9% (8/35) on control; risk difference -20.0 percentage points (95% CI -35.0 to -5.0), risk ratio 0.12 (0.02–0.95); unadjusted two-proportion z-test p = 0.012.

8. Statistical Interpretation

9. Statistical Methods Explained

The primary result compares the number of participants who met a binary endpoint in each randomized group. The registry reports event counts and group sizes, and the comparison is expressed as a risk difference. The estimate is -0.2 for intervention minus control. In general, a risk difference subtracts the event proportion in the comparator group from the event proportion in the intervention group. A value below zero means the observed event proportion was lower in the intervention group; it does not by itself establish why the groups differed.

What does the risk difference describe?

For a binary outcome, each participant is classified as having or not having the specified event. The event proportion is the number meeting the definition divided by the number in that group. A risk difference places the contrast on an absolute scale: it describes the separation between the two proportions, rather than their relative size. The estimate depends on the endpoint definition, the participants included, and the follow-up period. Here, the endpoint is clinically significant leukopenia during one year following transplant, as defined in the registry record.

The recorded risk difference is intervention minus control, so its negative sign corresponds to a lower observed proportion in the maribavir group. The risk difference is an estimate based on the observed trial participants, not a guarantee that the same contrast would occur in another population. Its uncertainty is represented by the reported confidence interval. Because the interval is entirely on the negative side of zero, its direction is consistent with the point estimate; the breadth of the interval still matters for judging how precisely the size is known.

How should the p value be read?

The registry posts an unadjusted p value of 0.012. In general, a p value is calculated under a statistical model that assumes a null hypothesis, such as no group difference. It quantifies how unusual data at least as incompatible with that null model would be, if the model and its assumptions were correct. It is not the probability that the null hypothesis is true, and it is not the probability that the result is due to chance. A p value also does not communicate the magnitude or practical importance of a difference; the estimate and its interval are needed for that context.

The registry record does not identify the test used to obtain the posted p value, nor does it report whether the analysis was adjusted for other factors. The p value should therefore be described as posted, unadjusted, and not as evidence of a particular adjusted analysis. The registry record does not report a multiplicity plan, so it is not possible to determine from the record whether the p value was intended as a single confirmatory test or how it would be interpreted alongside other outcomes.

What does randomization contribute?

In general, random assignment is intended to make treatment groups comparable, on average, with respect to factors measured and unmeasured before assignment. It supports an interpretation focused on the assigned groups, provided the analysis and follow-up preserve the randomized comparison. The registry identifies the study as randomized, but it does not report allocation-concealment procedures, the analysis population, or how participants with missing outcome data were handled. Those details affect how fully the posted comparison can be evaluated.

The record lists masking as none. General statistical reasoning recognizes that knowledge of assignment may influence some measurements or management decisions, depending on how outcomes are defined and assessed. Since this endpoint requires an adjustment to mycophenolate or antiviral prophylaxis as well as a low white blood cell count, details of decision procedures could help readers assess the possibility of differences in event classification. Such procedures are not reported in the registry record, so no claim about their influence is warranted.

Why do event counts matter?

For a binary endpoint, each event contributes to the estimated group proportion. When the event counts are limited, adding or reclassifying a small number of participants can have a noticeable effect on the estimate. This is a general property of sparse binary data, not a claim that any posted event was misclassified. The confidence interval reflects uncertainty in the estimated contrast, while the counts make the amount of observed information visible.

General statistical explanation: a confidence interval is a range produced by a method designed to express uncertainty about an estimate under specified assumptions. Its endpoints are not a guarantee that the true value lies in that particular interval, and it does not describe the range of individual participant outcomes. The registry gives a confidence interval for the risk difference but does not state its confidence level or provide the method used to calculate it.

The reported comparison is unadjusted, and the record does not report a model incorporating covariates or a time-to-event analysis. The endpoint is posted as a count of participants with an event, rather than total event episodes or time until an event. As a result, interpretation should remain tied to the participant-level endpoint and its stated timeframe.

10. Confidence Intervals and Precision

The point estimate for the risk difference is -0.2, with intervention defined as the maribavir group and control as the valganciclovir group. The registry also reports a confidence interval for this contrast. Its endpoints are on the negative side of zero, so the full reported interval is consistent with a lower observed endpoint proportion in the intervention group. The confidence level and calculation method are not reported in the registry record.

In general, a confidence interval conveys uncertainty around an estimate under a particular statistical procedure. A narrower interval indicates greater precision in the estimate under that procedure; a wider interval indicates greater uncertainty about the size of the contrast. It is not a range containing a specified proportion of individual participant outcomes, nor does it establish that every value within it is equally plausible.

The event counts are 8 of 35 in the control group and 1 of 35 in the intervention group. With event counts of this size, the estimate should be read alongside its interval rather than as an exact measure of a stable underlying difference. The direction of the estimate is clear in the posted comparison, but its magnitude is less certain than a single point estimate might suggest.

The interval does not address every limitation of the comparison. It does not account automatically for unreported features such as missing-data handling, outcome-assessment procedures, or potential multiplicity. The registry record does not report the analysis population or the method used for the interval. The confidence interval therefore helps convey statistical uncertainty in the reported contrast, while questions about analysis and study conduct remain relevant to interpretation.

11. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The planning figures are participants per arm, not total events. They are illustrations based on the observed effect and are not the trial’s original design calculation. The stated planning assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect to detect is set to a stated fraction of the observed effect.

For planning at 100% of the observed effect, the illustration gives 43 participants per arm for 80% power and 57 participants per arm for 90% power. For planning at 75% of the observed effect, it gives 90 participants per arm for 80% power and 120 participants per arm for 90% power. For planning at 50% of the observed effect, it gives 230 participants per arm for 80% power and 307 participants per arm for 90% power.

In general, power is the chance that a planned statistical test will reject its null hypothesis under a particular assumed effect and analysis model. The 80% and 90% columns describe different planning targets: the 90% target seeks a higher chance of detecting the assumed effect, and therefore requires more participants in these illustrations. Smaller assumed effects also require more participants, as the listed scenarios show.

The original trial’s sample-size assumptions and justification are not reported in the registry record. These figures are retrospective planning illustrations based on the observed effect; they are not observed power and do not describe the probability that this completed trial detected a true effect. The curve visualizes the same planning relationship, rather than a separate observed outcome.

12. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, p₀ and p₁ are the control and treatment proportions, and p̄ is their average.

Worked calculation for this trial

1. Control proportion p₀ = 0.229; treatment proportion p₁ = 0.029; average p̄ = 0.129.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.4734 = 0.9278.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.4518 = 0.3802.
4. n = (0.9278 + 0.3802)² / (-0.2000)² = 42.8, rounded up to 43 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
p0 <- 0.228571428571429                          # control proportion
p1 <- 0.0285714285714286                          # treatment proportion
n_per_arm <- function(power, frac = 1) {
  q1 <- p0 + (p1 - p0) * frac               # smaller effect = fraction of the observed difference
  pbar <- (p0 + q1) / 2
  z_b <- qnorm(power)
  ceiling(round((z_a * sqrt(2 * pbar * (1 - pbar)) + z_b * sqrt(p0 * (1 - p0) + q1 * (1 - q1)))^2 / (q1 - p0)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (unrounded n per arm)
cat("power.prop.test:", round(power.prop.test(p1 = p0, p2 = p1, power = 0.80)$n, 1), "\n")

# Simulation: how often does the z-test reject at the 80%-power sample size?
set.seed(6034925)
n    <- n_per_arm(0.80)
reps <- 20000
x0 <- rbinom(reps, n, p0); x1 <- rbinom(reps, n, p1)
ph <- (x0 + x1) / (2 * n)
z  <- ((x1 - x0) / n) / sqrt(ph * (1 - ph) * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(z) > z_a, na.rm = TRUE), reps))

Output from running the code

100% of observed effect: n per arm = 43 (80% power), 57 (90% power)
 75% of observed effect: n per arm = 90 (80% power), 120 (90% power)
 50% of observed effect: n per arm = 230 (80% power), 307 (90% power)
power.prop.test: 42.8 
Simulated power at n = 43 per arm: 0.873 (20000 replicates)

The simulation draws many pairs of event counts at the planned sample size and counts how often the two-proportion z-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

13. Multiplicity, Missing Data and Analysis Populations

The registry record posts one primary result for clinically significant leukopenia and lists no posted secondary outcome results. It does not report a multiplicity plan describing how statistical testing across outcomes or comparisons was to be handled. The posted p value is unadjusted. Without a stated analysis plan, it is not possible to determine whether this was intended as the sole confirmatory comparison or how other analyses were meant to affect interpretation.

The record does not report how missing outcome data were handled, whether all randomized participants were included in the primary analysis, or what analysis population was specified. It also does not describe a method for dealing with participants who did not complete follow-up through the one-year endpoint timeframe. These are not details that can be inferred from the group counts alone. The counts and group sizes describe the posted result, but the registry record does not state the analysis rules that produced them.

The registry does identify the trial as randomized and open-label. It does not report allocation concealment, blinding of endpoint assessment, an adjustment strategy, or an interim-analysis plan. These omissions limit the ability to assess whether the reported comparison followed a prespecified analysis framework or whether choices were made after seeing the data.

General statistical explanation: testing multiple outcomes or repeatedly examining accumulating data can affect the interpretation of nominal p values if the analysis does not account for those features. That general concern does not establish that this trial conducted unreported tests or interim analyses. The registry record does not report such plans, and their presence or absence should not be guessed.

The posted primary result can be described as the registry reports it, with these uncertainties kept distinct from the result itself. No secondary results are available in the registry record to support a broader comparison of efficacy or tolerability outcomes.

14. 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

Serious events with the highest arm-level rate: graft loss (5.7%).

The registry reports serious adverse events among 2 of 35 participants in the control group and 1 of 35 participants in the intervention group. It reports other adverse events in 0 of 35 participants in each group. Deaths are listed for 1 participant in each group. These are counts, not a statistical comparison adjusted for follow-up or other factors.

Graft Loss is listed among the serious adverse event terms at 5.7%. The registry record does not provide further context for that term in the material, such as its relationship to the overall serious-event counts or the participants affected. The term should therefore be read as a listed serious adverse event, without inferring additional details.

In general, adverse-event counts describe what was recorded in the study, but small counts provide limited information about differences between groups. They do not establish that an event was caused by a regimen, and they do not summarize every aspect of tolerability. The registry record does not report detailed event timing, severity beyond the serious-event classification, or causal attribution. The safety counts should be considered separately from the primary leukopenia endpoint, which has its own definition and comparison.

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

The posted primary result shows fewer participants meeting the registry’s clinically significant leukopenia definition in the maribavir group than in the valganciclovir group: 1 of 35 compared with 8 of 35. The estimated risk difference is -0.2 for intervention minus control, and the posted confidence interval lies entirely below zero. The unadjusted p value is 0.012. These findings describe the observed comparison in this randomized trial.

The result does not by itself establish why the observed groups differed, nor does it establish that the same difference would occur in another group of patients. The interval indicates uncertainty about the size of the contrast, and the relatively limited event counts make that uncertainty important. The record’s lack of detail about missing data, analysis populations, masking, and endpoint-assessment procedures also limits how completely the analysis can be evaluated.

The endpoint is about leukopenia meeting a definition that includes a treatment adjustment. It is not a direct measure of CMV infection, and the primary result does not answer whether one regimen prevents CMV more effectively. The registry’s stated purpose includes CMV prevention, but no secondary results are posted in the record. The leukopenia finding should not be extended to unreported outcomes.

The serious adverse-event counts are descriptive and do not establish a comparative safety profile. The registry reports 2 participants with serious adverse events in the control group and 1 in the intervention group, with 1 death in each group; the record does not provide enough detail to infer causal relationships or broader safety differences.

Overall, the data show a lower observed frequency of the defined primary endpoint in the intervention group, with statistical evidence of a difference in the unadjusted comparison. The scope of that statement is limited to this endpoint, this comparison, and the information posted in the registry record.

16. Why This Trial Matters Statistically

This trial illustrates how a tolerability outcome can be defined more specifically than a laboratory threshold alone. Clinically significant leukopenia required both a white blood cell count <3,000 cells/mm3 and an adjustment in mycophenolate or antiviral prophylaxis. That definition focuses the outcome on a low count linked to a management change, but it also means that assessment and treatment decisions are part of how the endpoint is determined.

The primary comparison is based on a randomized parallel-group design, with 35 participants in each group in the posted result. The event counts differ, and the estimated risk difference is -0.2. Considering the estimate together with its confidence interval and the unadjusted p value illustrates why statistical interpretation should address both direction and uncertainty, rather than relying on a single threshold or number.

The registry record also demonstrates the importance of distinguishing outcomes that answer different clinical questions. Leukopenia is a tolerability-related endpoint; it is not a CMV infection endpoint. A study may have broader aims, but conclusions should follow the outcomes for which results are posted. Here, the record does not post secondary results that would answer the CMV-prevention question.

Finally, the record leaves important analysis details unreported, including missing-data handling, analysis populations, multiplicity, and the trial’s original sample-size justification. These omissions do not erase the posted comparison, but they define how far readers can assess its statistical framework. The planning illustrations also show why sample-size interpretation must distinguish a retrospective illustration from the original study design and from observed power.

17. 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 posted primary result has limited event counts: 8 participants met the endpoint in the control group and 1 in the intervention group. The estimate and its confidence interval should therefore be interpreted with attention to uncertainty in the size of the difference. The registry record does not report a confidence level or the method used to calculate the interval.

The study is listed as open-label. Because the primary endpoint definition includes an adjustment to mycophenolate or antiviral prophylaxis, information about decision rules and outcome assessment would help readers evaluate how consistently the endpoint was applied. Those procedures are not reported in the registry record. This is a limitation in what can be assessed, not evidence that the outcome was assessed differently between groups.

The record does not report the analysis population, missing-data methods, multiplicity plan, interim-analysis plan, or original sample-size justification. It also does not provide secondary outcome results. The posted primary result therefore cannot be used to assess unreported outcomes or the full analysis framework.

The endpoint is limited to clinically significant leukopenia during one year following transplant; it does not describe all low blood counts, their duration or severity, or CMV infection outcomes. The brief summary describes maribavir plus acyclovir, while the intervention arm description lists maribavir 400mg twice daily without mentioning acyclovir. Additional regimen details are not reported in the registry record. These limitations define what the posted information can support without implying unreported trial findings.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Maribavir vs. Valganciclovir for CMV Prophylaxis in High-Risk Kidney Transplant Recipients — NCT06034925.
• Registry record last updated 2026-04-30; status last verified 2026-04.
• Results first posted 2026-04-30.
• 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.

21. Record Summary

The registry describes a completed, phase 4 randomized, open-label, parallel-group trial comparing maribavir with valganciclovir for CMV prophylaxis in high-risk kidney transplant recipients. Enrollment is listed as 70, with 35 participants in each group in the posted primary result. The recorded start date is 2023-11-06, and the primary completion date is 2025-06-30.

The primary endpoint is clinically significant leukopenia during one year following transplant, defined by a white blood cell count <3,000 cells/mm3 together with an adjustment in mycophenolate or antiviral prophylaxis. The posted counts are 1 of 35 in the maribavir group and 8 of 35 in the valganciclovir group. The risk difference is -0.2, with an unadjusted p value of 0.012 and a reported confidence interval entirely below zero.

The registry record does not report secondary results, the trial’s original sample-size justification, or key analysis details including missing-data handling and analysis populations. The primary finding concerns leukopenia and does not establish a comparison of CMV infection outcomes.