Effectiveness of OZ439 as a Gametocytocidal and Transmission Blocking Agent: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Effectiveness of OZ439 as a Gametocytocidal and Transmission Blocking Agent (NCT02431650), a randomized phase 1, phase 2 study. The primary outcome is Infection Success of Vector Mosquitoes.

2. Clinical Question

This was a proof-of-concept study in an experimental infection setting, not a description of routine clinical care. Its stated purpose was to assess OZ439 as a gametocytocidal agent and examine treatment effects on gametocyte infectivity and development in vector mosquitoes. The record describes piperaquine as being used in the study context because previous clinical studies, including an IBSM study, had shown production of gametocytes after a single dose.

The primary endpoint therefore addresses a biological transmission outcome rather than a symptom, clinical recovery measure, or direct measure of parasite clearance. Mosquito feeding was performed by direct feeding on participants and by artificial membrane feeding. The registry does not report results separately for those feeding approaches in the posted primary outcome description.

The reported endpoint is limited to the participants for whom transmission was determined. Because that group is smaller than total enrollment, the posted result describes the assessed participants rather than all enrolled participants. Whether the assessed group differed from those not assessed, and why assessment was unavailable for some participants, are not reported in the registry record.

3. Trial Design

This was a randomized, controlled, open-label, parallel-group study listed as Phase 1 and Phase 2. It was conducted at a single centre and enrolled 11 participants. The registry lists Medicines for Malaria Venture as the sponsor, a start date of 2015-04, a primary completion date of 2016-09, and a completed status.

The two arms were Primaquine 15mg, identified as the control, and OZ439 500mg. The study description says participants were randomized into experimental or control groups when peak gametocytemia occurred, approximately 15 days after piperaquine administration. It describes up to 3 cohorts, with n=2 per group at that stage. These are protocol-description details; the final registry arm entries list n=3.0 for Primaquine 15mg and n=4.0 for OZ439 500mg. The record does not explain how the cohort description relates to the final arm counts.

Participants were inoculated on Day 0 with Plasmodium falciparum-infected human erythrocytes. The arm descriptions state that a single dose of 480 mg of piperaquine was administered when PCR quantification reached the specified threshold, although the registry text for those descriptions ends mid-sentence. No further dosing details should be inferred from that incomplete text.

Open-label means that masking was not used, according to the registry. Random allocation can help make comparison groups more comparable in expectation, but it does not eliminate uncertainty, particularly in a small study. The registry does not report the randomization sequence method, allocation concealment, blinding of mosquito outcome assessment, or other procedures that would clarify how allocation and assessment were implemented.

The main outcome was infection success in vector mosquitoes, measured over the stated period from day 10 to 21 after piperaquine dosing. The registry also lists safety as a secondary outcome, expressed as number of adverse events. Details of a protocol, statistical analysis plan, or prespecified sample-size justification are not reported in the registry 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.

Overall Study

Analysis population for the primary outcome, as defined in the registry: Transmission of gametocytes to mosquitos was only determined for 7 of the 11 subjects that participated in the trial. Transmission of gametocytes to mosquitoes was observed in 5 of the 7 subjects analysed.

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 Infection Success of Vector Mosquitoes, measured over From day 10 to 21 post Piperaquine dosing.

The primary endpoint is titled “Infection Success of Vector Mosquitoes.” It counts participants with transmission detected, with the registry describing detection of oocysts in mosquito midgut preparations after direct feeding on participants or indirect artificial membrane feeding. The stated timeframe is from day 10 to 21 after piperaquine dosing.

This endpoint is used because the study sought to assess whether gametocytes could infect mosquitoes, an outcome relevant to the parasite’s transmission stage. It is distinct from measuring parasite levels in participants: a mosquito infection outcome reflects transmission under the study’s feeding procedures. It also does not, by itself, establish how frequently transmission would occur outside the experimental setting.

The record reports that transmission was determined for 7 of the 11 participants and observed in 5 of those assessed. The arm entries record 2.0 participants with the endpoint among 3.0 in the Primaquine 15mg group, and 3.0 among 4.0 in the OZ439 500mg group. These are participant counts, not a reported adjusted comparison or effect estimate. The registry does not report separate results for direct and membrane feeding, the number of mosquitoes assessed per participant, or further details of the endpoint adjudication.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is a binary participant-level outcome: a participant either had transmission detected in the mosquito assessment or did not. The registry presents counts of participants with the event, rather than a continuous measurement such as a laboratory concentration. It describes the event as oocyst detection in mosquito midgut preparations after direct or membrane feeding. The record does not report a statistical model fitted to this outcome.

What do participant counts tell us?

Counts retain a direct link to observed outcomes: they indicate how many assessed participants had the event in each arm. The denominator matters because the same count can have different meaning in groups of different sizes. Here, arm-level denominators and event counts are recorded, while an overall statement says transmission was assessed in only part of the enrolled group. These observed counts can be described, but they do not by themselves provide a formal estimate of comparative uncertainty.

General statistical explanation: a binary outcome can be analysed using methods designed for event probabilities, such as a comparison of proportions or a regression model for binary data. The choice depends on the design, prespecified estimand, and analysis plan. A model may account for specified covariates or design features, but adjustment should not be assumed unless reported. The registry does not report which model, if any, was prespecified for the primary outcome.

Why is an inferential comparison absent?

The record lists no posted analyses and states that values are missing or not estimable for a two-arm comparison of this binary endpoint. Consequently, it does not give a sponsor-reported estimate comparing the arms, a confidence interval, or a p-value. An observed count comparison is not equivalent to a completed inferential analysis. Without an analysis method and uncertainty measure, readers cannot use the registry result to determine the precision of a relative effect.

General statistical explanation: a confidence interval expresses uncertainty around an estimate under a particular method and assumptions. A narrow interval generally indicates greater precision than a wide interval, but an interval’s interpretation depends on the design and analysis. A p-value is not the probability that a treatment effect is true; it describes how compatible the observed data are with a specified null model, assuming the model and analysis conditions. Neither quantity is reported for this primary comparison.

How does randomization enter the interpretation?

The study is listed as randomized, which indicates that allocation was intended to use chance. Randomization can reduce systematic differences between groups at allocation, but it does not guarantee balance in a small trial. It also does not resolve outcomes that were not determined or ensure that outcome assessment was unbiased. The sequence-generation method, allocation concealment, and masking of outcome assessors are not reported in the registry record. The study is explicitly listed as open-label with no masking.

General statistical explanation: an intention-to-treat analysis usually evaluates participants according to their randomized groups, while other analysis populations can be defined for different purposes. Which populations were used, how participants with unavailable outcomes were treated, and whether any sensitivity analyses were planned are not reported in the registry record. The arm counts should therefore be read as posted, without assuming a particular analysis population beyond what the record states.

What do the planning assumptions mean?

The record describes sample-size illustrations based on the observed effect, equal allocation, a two-sided significance level of 0.05, and a normal approximation; the target effect is stated as a fraction of the observed effect. These are planning assumptions, not evidence about the trial’s design rationale and not a measure of observed power. The sample-size justification used when designing the trial is not reported in the registry record. The numerical planning outputs are not stated in the record details.

General statistical explanation: planning calculations estimate how many participants might be needed under assumptions about the effect to detect, variability, allocation, and error rates. They do not change what was observed, and they should not be presented as “observed power.” If planning is anchored to an observed effect, the illustration is conditional on that estimate and may not represent the effect expected in a future study.

General statistical explanation: over-dispersion matters when count data vary more than a statistical model expects, because standard errors may then be too small if that extra variation is ignored. This endpoint is reported as counts of participants with a binary event, not as a participant-level count of repeated events. The record does not report an over-dispersion assessment or a model requiring such an assessment; this concept should not be mistaken for a method used in the analysis.

The registry also does not report interim analyses, stopping rules, covariate adjustment, treatment-effect estimands, or a statistical analysis plan. These details should not be inferred from the trial’s phase, design labels, or outcome counts. The most defensible statistical reading is therefore descriptive: the posted counts characterize assessed participants, while formal comparative uncertainty and analysis details remain unavailable.

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("Primaquine 15mg", "OZ439 500mg")
n      <- c(3, 4)
events <- c(2, 3)
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  Primaquine 15mg  3  2  66.7  9.4  99.2  20.8  93.9  19.4  93.2
ARM  OZ439 500mg  4  3  75.0  19.4  99.4  30.1  95.4  28.4  94.7

11. Multiplicity, Missing Data and Analysis Populations

The registry lists 2 outcome measures and 1 posted secondary outcome, identified as safety: number of adverse events. It lists 0 posted analyses. The record does not state whether the primary outcome was tested alongside other outcomes under a formal testing strategy, whether any multiplicity adjustment was planned, or which outcome was designated for confirmatory inference beyond the registry’s primary-outcome label. A multiplicity procedure is therefore not reported in the registry record.

Transmission was assessed for 7 of the 11 enrolled participants. The reason the endpoint was not determined for all participants is not reported in the registry record. Nor does the record describe imputation, exclusion rules, sensitivity analyses, or a missing-data assumption. The available endpoint results should be understood as describing those assessed, without assuming that unavailable outcomes were absent or similar to observed outcomes.

The record does not specify an intention-to-treat, per-protocol, or other analysis population for the primary endpoint. The reported arm counts and the overall assessed-participant statement are available, but their relationship to a prespecified analysis population is not explained. No interim analyses or monitoring-based stopping decisions are reported in the registry record. A sample-size justification and detailed statistical analysis plan are also not reported. These omissions limit the ability to assess how endpoint selection, missing observations, and multiple outcomes may have affected the reported interpretation.

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 registry lists serious adverse event counts by group. For Primaquine 15mg, 0 serious adverse events are recorded among 5 participants at risk. For OZ439 500mg, 0 are recorded among 6 participants at risk. The registry also records 0 deaths in each group. These are the posted serious-event and death counts; they should not be treated as proof that serious harms cannot occur.

The same safety entry lists other adverse events affecting 4 of 5 participants at risk in the Primaquine 15mg group and 2 of 6 in the OZ439 500mg group. These are distinct from the serious adverse event counts. The registry does not provide event-level descriptions for these other adverse events in the information, and the serious-event terms list is empty.

Safety counts are descriptive in a study of this size. They do not establish a comparative safety profile or quantify risk precisely. The record does not report severity grading, duration, relatedness assessment, exposure-adjusted rates, or a safety analysis plan. The number at risk is the registry’s stated safety denominator and should not be assumed to be interchangeable with the number assessed for the primary transmission endpoint.

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

The posted result establishes that mosquito transmission was detected for 5 of the 7 participants assessed for the primary outcome. The arm entries record transmission in 2.0 participants in the Primaquine 15mg group and 3.0 participants in the OZ439 500mg group, with their respective registry denominators. This is a description of the observed study data, not a precise estimate of comparative effect.

The registry does not provide a formal two-arm analysis, confidence interval, or p-value for the endpoint. Therefore, the observed counts do not tell readers how compatible the results are with a range of possible treatment effects or how much random variation may have influenced the apparent group pattern. The missing assessment for some enrolled participants adds uncertainty, and the reason and handling of those unavailable outcomes are not reported.

The biological context is specific: experimental Plasmodium falciparum blood-stage infection, gametocyte assessment, and direct or membrane mosquito feeding. These measurements are relevant to the study’s transmission question, but they are not the same as measuring clinical illness, patient-important outcomes, or transmission under ordinary conditions. The record does not report a basis for extending the findings to settings or groups outside the trial.

The study description states a proof-of-concept aim: to assess OZ439 as a gametocytocidal and transmission-blocking agent. The registry outcome counts should be read within that aim and the limits of the reported data. They do not, by themselves, settle whether the arms differed in transmission, establish the size or precision of any difference, or support conclusions about outcomes not measured in the record. The appropriate statistical reading is descriptive and cautious, with attention to the limited assessed group and the absent inferential analysis.

14. Why This Trial Matters Statistically

This trial is statistically notable because it measures a transmission-related endpoint in an experimental infection study rather than relying only on participant parasite measures. Mosquito oocyst detection provides a direct endpoint tied to the stated question of whether gametocytes can infect vector mosquitoes under the study’s feeding procedures. That makes the endpoint aligned with the proof-of-concept aim, while also making its interpretation dependent on the experimental assessment context.

The record illustrates why denominators and analysis populations matter. Total enrollment was 11, but the primary endpoint was determined for 7 participants. A reader needs both the number with transmission detected and the number assessed to understand the reported result. Because the record does not explain why the endpoint was unavailable for other enrolled participants, the observed findings cannot automatically be generalized to everyone enrolled.

It also shows the distinction between descriptive data and comparative inference. Randomization is a design feature, but the registry lists no posted analysis for the binary primary outcome. Without an estimate and uncertainty measure, the arm counts alone cannot answer how precise a between-group comparison would be. The small arm entries make this especially consequential: individual outcomes form a substantial part of the available evidence, and the record does not supply a formal method to quantify the uncertainty.

Finally, the record separates an experimental transmission endpoint from safety reporting. It lists serious-event and other adverse-event counts, but those counts are descriptive and limited to the recorded safety groups. Together, the trial’s endpoint and reporting gaps underscore the value of clear analysis plans, transparent missing-outcome handling, and uncertainty estimates when interpreting small clinical studies.

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 was assessed for 7 of the 11 enrolled participants, and the registry does not explain why it was not determined for the others. This limits the scope of the observed endpoint result and leaves uncertainty about whether unassessed participants could have changed the descriptive pattern. Missing-data methods and sensitivity analyses are not reported.

The registry lists small arm counts for the endpoint: n=3.0 in the Primaquine 15mg arm and n=4.0 in the OZ439 500mg arm. It does not post an inferential comparison, an uncertainty interval, or a p-value. As a result, precision cannot be evaluated from a sponsor-reported comparative analysis. The registry states that values are missing or not estimable for a two-arm comparison of this binary endpoint.

The trial was open-label, and masking was not used. Whether mosquito outcome assessors were masked is not reported. The record also does not report randomization methods or allocation concealment, and therefore does not permit detailed assessment of those design safeguards. Results are tied to experimental infection and the specified mosquito feeding procedures; separate results by feeding method are not reported.

Other limitations in the registry record include the absence of a reported sample-size justification, statistical analysis plan, multiplicity approach, interim analysis details, and defined analysis populations. The protocol description mentions up to 3 cohorts and n=2 per group at the time peak gametocytemia occurs, while final arm entries list different group sizes; how these descriptions relate is not explained. These limitations affect interpretation of both the endpoint counts and the broader study design.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Effectiveness of OZ439 as a Gametocytocidal and Transmission Blocking Agent — NCT02431650.
• Registry record last updated 2020-05-26; status last verified 2020-05.
• Results first posted 2020-05-26.
• 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.

19. Record Summary

NCT02431650 is a completed, randomized, open-label, parallel-group Phase 1 and Phase 2 study sponsored by Medicines for Malaria Venture. The registry lists enrollment of 11 and describes experimental Plasmodium falciparum blood-stage infection. Participants were assigned to OZ439 500mg or Primaquine 15mg, with piperaquine described in the infection study sequence.

The primary outcome was infection success in vector mosquitoes, assessed by oocyst detection after direct or membrane feeding from day 10 to 21 after piperaquine dosing. Transmission was assessed for 7 participants and observed in 5. The arm entries record 2.0 participants with the endpoint among 3.0 in the Primaquine group and 3.0 among 4.0 in the OZ439 group. No two-arm analysis is posted for this binary endpoint.

The registry lists safety as a secondary outcome and records no serious adverse events or deaths in either group. Reasons for unavailable primary endpoint assessments, missing-data handling, a statistical analysis plan, and a sample-size justification are not reported in the registry record.