A Study to Evaluate AAV9 Neutralizing Antibody Seroconversion in Household Contacts.: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for A Study to Evaluate AAV9 Neutralizing Antibody Seroconversion in Household Contacts. (NCT04543357), a registered phase not stated study. The primary outcome is Number of Participants (Previously Seronegative for Neutralizing Antibodies [NAbs] to AAV9) Who Developed NAb to AAV9 at Day 28 After the Interventional Study Patient Was Dosed.

2. Clinical Question

This question is specific to a selected household-contact population and a defined period after the patient’s dose. It is not a direct evaluation of the gene therapy’s effect in patients, and it does not by itself establish how any antibody change occurred. The outcome is a laboratory-defined antibody event, not a clinical outcome. The registry record does not report an estimate comparing contacts with people outside the household or with an untreated patient group.

3. Trial Design

NCT04543357 is a low-interventional study of AAV9 neutralizing antibody seroconversion in household contacts associated with C3391003. Pfizer is listed as the sponsor. The record gives a start date of 2022-08-17, a primary completion date of 2024-02-27, and a status of TERMINATED. A reason for termination is not reported in the registry record.

The described participants lived or worked in the same household as a patient in one of the fordadistrogene movaparvovec interventional studies. The brief summary says that up to 5 participants from the same household may be enrolled. The recorded enrollment is 8, but the registry record does not explain how many households contributed participants or how participants were distributed among households. The single listed group is “All participants,” described as household contacts of a DMD patient in an interventional study of fordadistrogene movaparvovec.

The listed intervention is a blood draw, categorized as OTHER. The study objective was to estimate the likelihood of AAV9 neutralizing antibody seroconversion in household contacts of a patient treated with fordadistrogene movaparvovec gene therapy in an interventional study. This is an observational antibody-monitoring question in contacts, not a randomized assignment of gene therapy to those contacts. The record does not give a comparator group, allocation procedure, blinding plan, or visit schedule beyond the outcome timeframes it names.

The registry lists four outcome measures and zero analyses. The primary outcome is a count of participants previously seronegative for AAV9 neutralizing antibodies who developed them at Day 28 after the interventional study patient was dosed. Named secondary outcomes concern anti-drug antibodies to AAV9 at Day 28 and Day 56. Detailed results for these outcomes are not reported in the registry record. Nor are a protocol, statistical analysis plan, sample-size justification, interim-analysis plan, or reason for study termination reported. The study dates and status describe the registry record; they do not establish why the study ended or whether every planned assessment was completed.

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 was a low-interventional study to assess development of neutralizing Antibodies (NAbs) to adeno associated virus serotype 9 (AAV9) in household contacts of Duchenne Muscular Dystrophy (DMD) Patients Treated with fordadistrogene movaparvovec.

Overall Study

Analysis population for the primary outcome, as defined in the registry: "Number of participants analyzed" signifies number of participants evaluable for the outcome measure: Participants with a NAb titer undetectable (ie, titer \<1) or detectable, but negative test (ie, titer \>=1 and \<4) at Baseline were included in the analysis.

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: All participants who signed the informed consent document, and 1) who were household members of interventional study participants (including siblings) who were assigned to fordadistrogene movaparvovec or placebo and received a single dose of study treatment and 2) who had at least one day of contact with the interventional study participant during the first 2 weeks.

6. Primary Endpoint

The registry lists the primary outcome as Number of Participants (Previously Seronegative for Neutralizing Antibodies [NAbs] to AAV9) Who Developed NAb to AAV9 at Day 28 After the Interventional Study Patient Was Dosed, measured over Day 28 after the interventional study participant was dosed.

The primary endpoint is the number of participants who were previously seronegative for AAV9 neutralizing antibodies and developed a neutralizing antibody to AAV9 at Day 28 after the interventional study patient was dosed. The outcome unit is participants, and the parameter is a count. The registry identifies the analysis population as participants with an undetectable baseline titer or a detectable but negative baseline test. The primary outcome result itself is not reported in the registry record.

Development is defined using a change from baseline. For a participant with a detectable but negative baseline test, defined as a titer of at least 1 and below 4, development requires an increase of at least 6-fold above the baseline titer. For a participant with an undetectable baseline titer, defined as below 1, development requires a titer of at least 6. These criteria distinguish a defined antibody event from simply having any detectable result. They also make baseline status central to deciding who is eligible for the primary analysis and how a subsequent measurement is classified.

A count is useful for reporting how many eligible participants meet a prespecified laboratory definition at a particular assessment time. It does not, on its own, express the event frequency in the eligible analysis population, quantify uncertainty, or compare risk with a control group. Those interpretations require the relevant denominator and, for uncertainty or comparison, appropriate statistical results. The registry record does not report the primary count, outcome-specific denominator, or an interval estimate.

The endpoint is an antibody measurement, not a clinical health outcome. It addresses whether antibody status changes by the specified time, not the consequences of that change. The registry record does not state that the endpoint is a surrogate for a clinical outcome, nor does it report any clinical effect inferred from it.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registered primary measure is a count: the number of eligible participants classified as developing an AAV9 neutralizing antibody by Day 28. A count records the number of people meeting a definition. To interpret it as a frequency, readers also need the number of people eligible for analysis and assessed at the relevant time. That denominator is not reported in the registry record. The enrollment figure is not necessarily the endpoint denominator because the record restricts eligibility for analysis according to baseline antibody status.

How does the endpoint classify development?

The registry defines the event by comparing antibody findings with baseline. Among participants whose baseline titer was detectable but negative, meaning at least 1 and below 4, development requires an increase of at least 6-fold above baseline. Among participants whose baseline titer was undetectable, meaning below 1, development requires a titer of at least 6. The criteria recognize that participants can begin with different baseline measurement states. They are classification rules for this endpoint; they should not be generalized to other laboratory tests or other studies without evidence that the same rules apply.

Baseline eligibility and outcome classification are related but separate steps. Eligibility determines which participants are included in the analysis population. The event definition then determines which eligible participants count as having developed the antibody. A participant who does not satisfy the baseline eligibility criteria is not part of the population described for the primary endpoint, regardless of the later measurement. The record does not report participant-level measurements or the number meeting either baseline category.

What can a count tell the reader?

A count can describe the number of observed events in the analysis population. By itself, it does not provide a proportion, because a proportion requires a denominator. It also does not measure precision: a count does not show how uncertain the result is as an estimate beyond the participants observed. Confidence intervals are a general statistical tool for expressing uncertainty around an estimate, but no interval for the primary outcome is reported in the registry record. No numerical inferential result is available to interpret.

For a binary outcome such as whether a participant meets an event definition, methods may estimate an event probability or compare probabilities across groups. Those approaches require careful definition of the analysis population and, for a comparison, appropriate groups and a prespecified contrast. This registry record identifies one group of household contacts and does not describe a like-for-like control comparison. It therefore does not provide a randomized treatment contrast for the primary outcome.

Why does over-dispersion matter in general?

In general, a simple count model may assume that the variability in counts follows a particular relationship to the expected count. If observed variability is greater than that assumption allows, the data are called over-dispersed relative to the model. Ignoring over-dispersion can make uncertainty estimates too small and statistical evidence appear more precise than it is. The issue often matters when counts vary substantially across settings or clusters. No count model, over-dispersion assessment, or model-based result is reported for this study. The primary measure is a participant count, and the registry record does not give enough outcome data to assess the distribution of counts.

Household membership could be relevant to statistical independence in a study with participants grouped within households: measurements from contacts in the same household might be more similar than measurements from unrelated households. This is a general design consideration, not a finding about this study. The brief summary allows up to 5 participants from the same household, but the record does not report the number of contributing households, household-level results, or whether an analysis accounted for clustering. It would therefore be inappropriate to assert that a particular dependence adjustment was used.

What is known about the planned sample-size illustration?

The record’s planning assumptions describe an illustration based on the observed effect, with a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. The effect to detect is described as a stated fraction of the observed effect. These assumptions are planning illustrations, not the trial’s own design or observed power. The registered study has a single listed group of household contacts, and the record does not report a trial-specific sample-size justification or design using those two-arm assumptions. No calculated illustration values are reported in the registry record information, so they cannot be used to infer an actual enrollment target or a result.

In general, a sample-size calculation asks what amount of information a planned design would need under specified assumptions. Its output depends on assumptions about the effect, variability, error rates, allocation, and analysis. A planning calculation does not show that a study had a particular probability of detecting an effect after data collection, and it does not replace an observed effect estimate or confidence interval. The registry record does not report the protocol assumptions that guided enrollment or any assessment of power using the final data.

Which statistical tests or models were used?

The registry record lists zero analyses. It does not report a statistical analysis plan, hypothesis test, regression model, adjustment strategy, interim analysis, or approach for multiplicity. No test statistic or p-value is available. A two-sided significance level in a planning illustration is not evidence that a particular analysis was conducted or that a result met a significance threshold. Statistical procedures should not be inferred from the endpoint’s count format or from the planning assumptions.

In general, an unadjusted analysis summarizes observed outcomes without controlling for other variables, while an adjusted analysis incorporates additional measured factors according to a model. Adjustment can be useful for particular research questions and designs, but it cannot create a randomized comparison when none is described. Since the record does not provide a model or adjusted estimate, neither an adjusted nor an unadjusted treatment effect can be attributed to this study. The central statistical limitation is not simply the choice of method: the primary outcome data and analysis results are not reported.

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("Participants With Potential Fordadistrogene Movapa")
n      <- c(3)
events <- c(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  Participants With Potential Fordadistrogene Movapa  3  0  0.0  0.0  70.8  0.0  56.1  0.6  60.2

11. Multiplicity, Missing Data and Analysis Populations

The registry record identifies four outcome measures, including the primary Day 28 count of participants developing AAV9 neutralizing antibodies and named secondary measures of anti-drug antibodies to AAV9 at Day 28 and Day 56. It does not report results for these outcomes, nor does it describe how the outcomes were prioritized for statistical testing beyond identifying one as primary. The details of the other outcome measures are not reported in the registry record.

Multiplicity arises in general when several outcomes, time points, subgroups, or statistical tests are examined. If many hypotheses are tested, the chance of at least one apparently notable result can increase unless the analysis plan addresses that issue. A prespecified hierarchy, adjustment procedure, or clear distinction between confirmatory and exploratory analyses can help readers understand how to interpret multiple findings. The registry record does not report a multiplicity procedure, a hypothesis-testing plan, or whether any secondary findings were intended to be confirmatory. With no analyses or outcome results reported, there is no basis to evaluate how multiplicity was handled in practice.

The outcome population is defined for the primary measure as participants who were baseline-seronegative under the registry’s titer criteria. The record does not report the number meeting those criteria, the number with an observed Day 28 result, or the handling of participants whose outcome measurement was missing. It also does not report whether participants withdrew, whether any measurements were invalid, or whether missingness was addressed through imputation or another method. These details are not reported in the registry record.

In general, missing outcome data can affect interpretation when availability is related to participant characteristics or the unobserved outcome. A complete-case analysis includes participants with observed measurements, whereas imputation methods use assumptions to represent missing values. Neither approach can be presumed. The recorded enrollment of 8 is not a substitute for the number analyzed for the primary endpoint, and no analysis population beyond the baseline eligibility description is documented in the available record.

The registry record does not report a protocol, statistical analysis plan, interim analyses, or rules governing analysis populations. As a result, it is not possible to determine whether the listed outcomes and time points were analyzed as originally planned, whether additional analyses were conducted, or how any such analyses would affect interpretation. The absence of these details limits assessment of selective reporting and the reproducibility of the statistical approach.

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 5% reporting threshold.

The registry lists a group titled “Participants With Potential Fordadistrogene Movaparvovec Exposure.” For serious events, it reports 8 participants at risk and 0 affected. For other events, it reports 8 participants at risk and 0 affected. The record also lists 0 deaths and no top serious-event terms. These are descriptive counts for the listed group, not evidence from a comparative safety analysis.

“At risk” identifies the group size used in the safety listing; it does not indicate that an event occurred. The count of 0 affected means that no such events are recorded for this group in the registry information. It does not establish that the underlying risk is zero or that an event could not occur in another population or under other circumstances. A zero count can remain compatible with uncertainty, particularly when the observation group is limited and no comparison group is described.

The registry record does not report event definitions, the duration of safety observation, event-level descriptions, or a comparison with an unexposed group. The exposure label refers to potential fordadistrogene movaparvovec exposure in the context of household contacts; it does not establish that the contacts themselves received the gene therapy. These safety counts are separate from the primary antibody endpoint and do not answer the seroconversion question.

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

The record establishes a research question and a laboratory definition: whether previously seronegative household contacts developed AAV9 neutralizing antibodies by Day 28 after the interventional study patient was dosed. It also describes an enrollment of 8, a blood-draw intervention, named antibody outcomes, and safety counts for a group with potential fordadistrogene movaparvovec exposure. These registry entries describe the registered study and its planned or listed measures.

The record does not report the observed primary outcome count, the number evaluable for that outcome, or a statistical estimate of seroconversion. Therefore, it does not show how many eligible contacts met the endpoint definition or how precisely the likelihood was estimated. The stated enrollment cannot fill that gap because the primary analysis population depends on baseline titer and an outcome assessment. No p-value, confidence interval, or model-based estimate is reported.

The result also cannot establish that any antibody change was caused by exposure through household contact. The listed group is not a randomized control comparison, and the record does not describe a comparable group without the relevant exposure. A laboratory change occurring after a patient’s dose would establish timing only if the data were available; timing alone would not isolate cause. The registry record does not report the data needed for that assessment.

The primary endpoint is an antibody classification, not a clinical outcome. The record does not establish that a change in this measure predicts a health outcome, has clinical consequences, or represents a broader effect of treatment. Nor does the study assess the treatment effect of fordadistrogene movaparvovec in the patients receiving it; the participants of interest are household contacts.

The safety listing reports no serious or other events in the listed group, while also giving the number at risk. These counts are descriptive and do not demonstrate that risk is absent. The study status is TERMINATED, but the reason is not reported in the registry record. Termination should not be interpreted as evidence for or against the endpoint, safety, or feasibility without further information.

The appropriate conclusion is limited: the registry record documents a planned assessment of AAV9 antibody status in household contacts and defines how the primary event would be classified, but it does not report the primary result or an analysis. That absence prevents a quantitative answer to the study’s central question. It is not evidence that seroconversion occurred, and it is not evidence that it did not occur.

14. Why This Trial Matters Statistically

This study is statistically distinctive because the question concerns antibody status in household contacts rather than treatment assignment among patients. The primary measure is defined as a participant count at a specified time after the interventional study patient was dosed. That framing makes population definition, baseline eligibility, and outcome ascertainment central to interpretation. Without knowing how many participants met the baseline criteria and had a Day 28 measurement, a count alone would not be enough to assess the event frequency.

The endpoint definition also illustrates why laboratory outcomes require operational rules. The registry distinguishes an undetectable baseline titer from a detectable but negative test, and applies a separate development criterion to each. This makes the outcome reproducible in principle, but the record does not report the participant-level or aggregate measurements needed to check how the rule was applied. A well-defined endpoint and a reported result are both necessary for readers to evaluate a study; one does not replace the other.

The study’s household context raises a general question about whether contacts from the same household may have related observations. The brief summary allows up to 5 participants from the same household. If observations are dependent within households, treating every person as statistically independent can understate uncertainty. The registry record does not report household-level data or an analysis accounting for such dependence, so this remains a design consideration rather than a confirmed analytical problem.

Finally, the record shows the difference between a scientific objective and an available statistical conclusion. It names an intended estimate, a primary endpoint, and secondary antibody time points, but lists zero analyses and reports no primary outcome result. The safety counts are also descriptive rather than comparative. This makes transparent reporting of analysis populations, missing measurements, effect estimates, and uncertainty especially important to any future interpretation of the study.

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 main limitation for interpreting this specific study is that the registry record does not report the primary outcome count or its analysis denominator. Although enrollment is 8, the primary endpoint includes participants meeting defined baseline seronegativity criteria, and the record does not say how many did so or had a Day 28 measurement. The record also does not report individual titer results, outcome summaries, or an estimate of seroconversion likelihood.

The study lists a single group of household contacts and does not describe a randomized or like-for-like control comparison. This limits what can be inferred about the source of any antibody change, even if an outcome result were available. The record does not report household-level distributions, so the extent to which participants were clustered within households is unknown. It also does not state whether statistical analyses accounted for potential within-household dependence.

The status is TERMINATED, but a reason for termination is not reported in the registry record. The record does not explain whether all planned outcome assessments were completed or whether termination affected data collection. It also does not report a protocol or statistical analysis plan, details of missing outcomes, rules for handling missingness, or any analysis population beyond the baseline eligibility description.

The record lists four outcome measures but does not report outcome results or analyses. It does not describe how multiplicity was handled across outcomes and assessment times, or whether the secondary outcomes were intended as confirmatory or exploratory. The named secondary antibody measures concern anti-drug antibodies, whereas the primary outcome concerns neutralizing antibodies; the registry record does not provide results that would permit their relationship to be assessed.

These limitations concern the information available in the registry record. They should not be read as proof that data were never collected or that no analysis exists elsewhere. The reason for termination, the complete analysis, and any further study results are not reported in the registry record.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: A Study to Evaluate AAV9 Neutralizing Antibody Seroconversion in Household Contacts. — NCT04543357.
• Registry record last updated 2025-02-26; status last verified 2025-02.
• Results first posted 2025-02-26.
• 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

NCT04543357 is a Pfizer-sponsored, low-interventional study of AAV9 neutralizing antibody seroconversion in household contacts of patients in an interventional study of fordadistrogene movaparvovec. The registry reports enrollment of 8, a blood draw, a start date of 2022-08-17, a primary completion date of 2024-02-27, and status TERMINATED. The reason for termination is not reported in the registry record.

The primary endpoint counts previously seronegative participants who developed AAV9 neutralizing antibodies at Day 28 after the interventional study patient was dosed. The registry defines baseline eligibility and antibody development criteria, but does not report the primary result, outcome denominator, or statistical analysis. Named secondary outcomes assess anti-drug antibodies at Day 28 and Day 56. Safety listings report 0 serious events and 0 other events among 8 participants at risk in the potential-exposure group. The record does not support a comparative safety conclusion or a quantitative answer to the primary research question.