Persistence of Antibodies in Adolescents and Adults 15 to 23 Years Who Received One Dose of Menactra® or Menomune®: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Persistence of Antibodies in Adolescents and Adults 15 to 23 Years Who Received One Dose of Menactra® or Menomune® (NCT00269477), a non-randomized phase 2 study. The primary outcome is Participants With Serum Bactericidal Activity of ≥ 1:8 for Each Menactra® Vaccine Serogroups Pre-vaccination and 28 Days Post-booster or Post-primary Dose Vaccination..

2. Clinical Question

The study was designed around two related questions: whether bactericidal antibody measurements remained above the stated threshold several years after earlier vaccination, and how those measurements changed after a Menactra® dose. The registry record describes booster vaccination in participants previously given Menactra® and primary vaccination in vaccine-naive participants. It also describes comparisons with age-matched controls in its study summary, but the study was non-randomized, so those groups should not be treated as interchangeable randomized arms.

The record’s primary endpoint is a count of participants meeting a threshold for each vaccine serogroup, assessed before and after vaccination. It does not provide the resulting counts or a direct numerical comparison. Therefore, the clinical question can be described from the study objective and endpoint definition, but the posted registry information does not establish how many participants met the threshold or how results differed between groups.

3. Trial Design

This was a Phase 2, non-randomized, unmasked, parallel-group study. The registry lists enrollment as 145 and status as completed. The recorded study start was 2005-12, and primary completion was 2007-02. The sponsor was Sanofi Pasteur, a Sanofi Company. The conditions listed were meningitis and meningococcal infection.

The study followed participants aged 15 to 23 years who had received meningococcal vaccination five years earlier. The study summary says the previously vaccinated participants had been vaccinated in Study MTA02 and did not participate in Study MTA19. Two groups are described as having previously received Menactra® and then receiving a booster dose. Two additional groups are described as meningococcal vaccine-naive and receiving a primary Menactra® dose. The endpoint timeframe refers to measurements five years after Menactra® or Menomune® vaccination, while the available group descriptions specifically identify prior Menactra® recipients.

Blood sampling was scheduled around vaccination. For the vaccine-naive groups, the record describes a pre-vaccination sample on Day 0, a Menactra® dose on Day 0, and further samples on Day 3, Day 7, and Day 28 in one group, or Day 5, Day 14, and Day 28 in the other. The descriptions of sampling schedules for the previously vaccinated groups are truncated in the registry record, so their full schedules are not reported there.

Non-random allocation and no masking limit the strength of between-group interpretation. Participants were grouped by vaccination history and sampling schedule, rather than randomly assigned to comparable conditions. The registry record explicitly cautions that the arms are not a like-for-like control comparison. It does not report additional details about allocation procedures or a statistical 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.

Before assignment: A total of 145 participants who participated in a previous study MTA02 and other meningococcal-vaccine naive participants were enrolled.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: SBA-BR titer for each of the 4 meningococcal serogroups in the vaccine was evaluated in the per-protocol population.

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 Participants With Serum Bactericidal Activity of ≥ 1:8 for Each Menactra® Vaccine Serogroups Pre-vaccination and 28 Days Post-booster or Post-primary Dose Vaccination., measured over 28 days post-vaccination (5 years after Menactra® or Menomune® vaccination).

The primary endpoint is the number of participants with serum bactericidal activity (SBA) at or above 1:8 for each of the four meningococcal serogroups in the Menactra® vaccine. Measurements were specified before vaccination and at 28 days after booster vaccination in the previously vaccinated groups or primary vaccination in the vaccine-naive groups. The record identifies the endpoint unit as participants and the analysis population as the per-protocol population.

SBA is a laboratory measure of the ability of serum to produce bactericidal activity against meningococcal serogroups. Using a threshold turns a continuous or titre-based laboratory measurement into a binary endpoint: a participant either meets the stated threshold for a given serogroup at a given assessment or does not. Reporting results for each serogroup separately matters because a participant may meet the threshold for one serogroup but not another.

As a general statistical point, a threshold-based endpoint is straightforward to describe as a count and proportion, but it does not show how far measurements lie above or below the cutoff. Its interpretation also depends on the chosen threshold and on complete, consistently timed measurements. The registry record does not provide the observed endpoint counts, proportions, uncertainty intervals, or detailed laboratory-analysis methods. Consequently, the endpoint’s definition is available, but its numerical findings cannot be interpreted from the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is binary at each serogroup and assessment: a participant either has an SBA result meeting the stated threshold or does not. A natural descriptive summary for such an outcome is the count meeting the threshold, alongside the number assessed. A proportion can also be useful, but interpreting one requires knowing its denominator and how missing measurements were handled. The registry record defines the endpoint as a participant count and identifies the per-protocol population, but it does not report the numerical outcome data or denominator for each analysis.

What does a threshold-based endpoint capture?

A cutoff makes laboratory results easier to summarize and compare, but it reduces detail. Participants with results just below the threshold and participants with much lower results fall into the same category; similarly, values just above and well above the threshold are counted together. This is a general feature of dichotomizing a measurement, not a finding specific to this study. The registry record does not provide the underlying titre distributions, so it is not possible to assess how close measurements were to the threshold or how sensitive conclusions might be to the cutoff.

There are four vaccine serogroups in the endpoint definition. Analyses across several serogroups can produce multiple related results. As a general statistical matter, examining multiple outcomes raises the question of whether the analysis plan controls the chance of false-positive findings across those outcomes. The registry record does not report a multiplicity procedure or describe how the serogroup-specific results were to be interpreted together.

Why does the non-randomized design matter?

Random allocation, when used appropriately, can help balance participant characteristics across groups. This study was non-randomized, and the groups were formed around prior vaccination status and dose context. Prior vaccination is central to the study question, but groups may also differ in other ways. As a general principle, a group difference in a non-randomized study cannot automatically be attributed to the exposure or vaccination history being compared. The registry record’s warning that the arms are not a like-for-like control comparison is consistent with that limitation.

The groups also received different types of vaccination in the study: previously vaccinated participants received a booster, while vaccine-naive participants received a primary dose. Thus, a direct comparison would combine differences in prior history and vaccination context. The record does not report an adjusted analysis that could account for measured differences, and it does not report details of any such model. No causal interpretation should be inferred from the design description alone.

How should uncertainty be considered?

A confidence interval is, in general, a range of values that reflects sampling uncertainty under a statistical model and analysis procedure. Narrower intervals usually indicate greater precision, while wider intervals indicate greater uncertainty. Confidence intervals for binary outcomes depend on the number of observations and the observed event proportion, among other choices. No confidence intervals for the primary endpoint are reported in the registry record, so the precision of the antibody findings cannot be judged from it.

Counts alone, even when available, would not answer whether a difference is precise or compatible with a range of possible effects. The primary result would need to be read with its analysis denominator, uncertainty estimate, and the design limitations. Here, numerical primary endpoint results and inferential analyses are not reported in the registry record. The record lists zero analyses, so no sponsor-reported primary endpoint test or estimate is available in the registry record.

What do the planning assumptions mean?

The record describes a planning illustration based on the observed effect, not the trial’s own design. Its stated assumptions are a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation; the effect to detect is expressed as a stated fraction of the observed effect. Such calculations are hypothetical planning aids. They do not describe the number of participants actually analyzed, do not show how the study was designed, and are not observed power. The record does not report a sample-size justification for the trial itself.

More generally, a planning calculation depends on assumptions about the effect size, allocation, outcome variability, significance level, and desired power. If the observed effect is used as the reference for a planning illustration, that effect may be an unstable estimate, especially when based on limited data. A planning result should therefore be understood as conditional on its assumptions, not as a guarantee that a future study will detect an effect or as evidence that the completed trial was adequately powered. The registry record does not report the numerical planning outputs in the registry record for this explanation.

For safety outcomes, the registry gives counts of participants affected and numbers at risk by group. These are descriptive counts. General comparisons of adverse-event proportions require attention to denominators, follow-up, event definitions, and uncertainty. The record does not report a formal comparative safety analysis, and no such inference should be drawn from the simple counts alone.

10. Multiplicity, Missing Data and Analysis Populations

The primary endpoint covers four meningococcal serogroups and includes assessments before vaccination and at 28 days after booster or primary vaccination. That structure creates several related measurements. As a general statistical matter, when multiple outcomes or comparisons are examined, a prespecified approach can help clarify whether results are confirmatory, exploratory, or adjusted for multiplicity. The registry record does not report a multiplicity adjustment, a hierarchy among serogroups, or a plan for interpreting several serogroup-specific results together.

The primary analysis population is identified as the per-protocol population. The registry record does not give the size of that population, its inclusion criteria, or the number of participants with evaluable measurements at each assessment. It also does not report how protocol deviations, incomplete blood samples, or missing endpoint values were handled. Imputation methods, if any, are not reported in the registry record.

These omissions matter because a per-protocol analysis can include fewer participants than enrolled, and the reasons for exclusion or missing measurement can affect interpretation. As a general principle, complete-case results may be biased if the availability of an outcome is related to the outcome itself or to participant characteristics. That possibility cannot be assessed without information on missingness and the analysis population.

The registry record lists no analyses. It does not report an analysis plan, a primary hypothesis-testing procedure, or whether any interim analyses were conducted. Those details are not reported in the registry record, so no specific testing strategy or missing-data assumption can be attributed to the study.

11. Safety Results

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

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 5.0% reporting threshold.

Most frequent non-serious adverse event terms

The registry record reports serious adverse-event counts by group. It lists zero participants with a serious adverse event among 9 at risk in Menactra® Vaccine Group 1, zero among 18 at risk in Menactra® Vaccine Group 2, zero among 58 at risk in Meningococcal Vaccine-naive Group 3, and zero among 60 at risk in Meningococcal Vaccine-naive Group 4.

These entries mean that no serious adverse events were recorded in the registry’s reported counts for these groups. They do not establish that the risk of a serious event is absent. A study with no recorded serious events can still be compatible with an underlying risk, and the registry counts alone do not quantify the precision of that risk estimate. The record does not provide confidence intervals or a formal comparison of serious adverse events between groups.

The registry also lists other adverse-event counts: 1 in Group 1, 5 in Group 2, 32 in Group 3, and 23 in Group 4. The registry record does not give the event terms in the registry record, so these counts cannot describe which events occurred or their severity. Death counts are not reported in the registry record. Differences in group size and non-random allocation also make simple count comparisons unsuitable as evidence of relative safety.

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

The study addresses persistence of bactericidal antibodies after earlier meningococcal vaccination and measurements after booster or primary Menactra® vaccination. Its primary endpoint is clearly specified as the number of participants meeting an SBA threshold for each vaccine serogroup before vaccination and at 28 days afterward. The study design and group descriptions provide context for those questions.

However, the registry record does not report the numerical primary endpoint findings. It does not show the counts meeting the threshold, corresponding analysis denominators, group comparisons, or estimates of uncertainty. Therefore, it cannot establish from these registry entries whether the threshold was commonly met, how results varied by serogroup, or how much measurements changed after vaccination. No conclusion about the magnitude or precision of the antibody findings is supported by the registry record alone.

The non-randomized design further limits between-group interpretation. Previously vaccinated participants received a booster, while vaccine-naive participants received a primary dose. Those groups differ in prior vaccination history by design and are not a like-for-like control comparison. A difference between them would not, on its own, isolate the effect of prior vaccination.

The registry’s safety counts show no recorded serious adverse events in the reported groups, alongside counts in an other-adverse-event category. These descriptive entries are not a complete comparative safety analysis and should not be read as proof that serious events cannot occur. The record also does not report death counts or the details needed to interpret the other adverse events.

In short, the registry record establishes what the investigators intended to measure and describes the study’s structure, but it does not contain the numerical primary result needed to judge the antibody endpoint. The trial’s findings should not be treated as evidence for or against a clinical outcome that was not reported in the record.

13. Why This Trial Matters Statistically

This study is statistically notable because its question involves antibody persistence over time and response after a subsequent dose, while its groups differ in prior vaccination history. That makes the distinction between a descriptive comparison and a causal comparison important. Non-randomized groups can be useful for describing measurements in specific participant groups, but between-group differences require careful interpretation when group membership is tied to prior exposure.

The endpoint also illustrates a common analytic choice: converting a laboratory measurement into a threshold-based count. Such an outcome is easy to communicate, but it discards information about the distance of each measurement from the cutoff. Results for each of the four serogroups must also be considered individually, and the registry record does not state how multiple related results were handled statistically.

The analysis population is identified as per-protocol, which highlights why enrollment and analysis denominators are not interchangeable. Without reported per-protocol counts, outcome counts, or handling of missing measurements, readers cannot assess how much data contributed to the primary endpoint or whether exclusions could affect interpretation.

Finally, the registry record describes no analyses and contains no numerical primary endpoint results in the registry record for this account. This limits what can be learned from the record despite its detailed objective and endpoint definition. The study is a useful example of why a trial’s question, design, analysis population, and posted numerical results all matter: a defined endpoint alone cannot establish the observed result or its precision.

14. 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 central limitation for interpretation is that the registry record does not report numerical results for the primary endpoint. It defines the outcome and assessment time but gives no group-specific counts, denominators, estimates, or uncertainty intervals. The antibody-persistence question therefore cannot be answered quantitatively from this record.

The study is non-randomized and unmasked. Previously vaccinated participants and vaccine-naive participants differ in prior vaccination history and received a booster dose or primary dose, respectively. The groups are not a like-for-like control comparison, as the registry record notes. Potential differences between groups cannot be separated from the effects of vaccination history using the design description alone.

The primary endpoint is based on a threshold for each serogroup. The registry record does not report underlying antibody measurements, laboratory-analysis details, or numerical results by serogroup. It also does not describe a multiplicity strategy, an analysis plan, or any statistical model. The analysis population is stated to be per-protocol, but its size and criteria are not reported in the registry record.

Handling of missing measurements and protocol deviations is not reported. The group descriptions for the previously vaccinated participants are truncated, so their full blood-sampling schedules are not available in the registry record. The record also does not report a trial-specific sample-size justification, interim analyses, or a detailed comparative safety analysis. These gaps constrain both the evaluation of the antibody findings and the interpretation of adverse-event counts.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Persistence of Antibodies in Adolescents and Adults 15 to 23 Years Who Received One Dose of Menactra® or Menomune® — NCT00269477.
• Registry record last updated 2016-04-14; status last verified 2016-04.
• Results first posted 2009-12-14.
• 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.

18. Record Summary

This completed Phase 2 study was non-randomized, unmasked, and parallel-group, with registry enrollment of 145. It examined antibody persistence after earlier meningococcal vaccination and measurements after booster Menactra® vaccination in previously vaccinated participants or primary Menactra® vaccination in vaccine-naive participants. The primary endpoint was the number meeting an SBA threshold for each of four vaccine serogroups before vaccination and at 28 days afterward, in the per-protocol population.

The registry record does not report numerical primary endpoint results or analyses. It lists zero serious adverse events in each reported group, with group-specific at-risk counts, but does not provide a formal comparative safety analysis. Non-randomized group assignment, absent primary results, and unreported details about missing data and analysis procedures limit interpretation.