This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for Antibody Persistence and Booster Dose Response in Subjects Who Received Menactra® Three Years Earlier in Study MTA26 (NCT00700713), a non-randomized phase 2 study. The primary outcome is Percentage of Participants With Serum Meningococcal Serogroups A, C, Y, and W-135 Bactericidal Antibody Titers ≥ 1:4 and ≥ 1:8 Before and Following Vaccination With Menactra®.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT00700713 |
| Phase | Phase 2 |
| Condition | Meningitis, Meningococcemia |
| Allocation | Non-Randomized |
| Design model | Parallel |
| Masking | None (open label) |
| Enrollment | 181 |
| Arms in the primary outcome | n/a |
| Lead sponsor | Sanofi Pasteur, a Sanofi Company |
| Results posted | Yes |
2. Clinical Question
Population
The study included toddlers who had participated in Study MTA26 and age-matched participants who had never received Menactra®. Antibody persistence and response were assessed in the Per-Protocol Analysis Set. The registry record describes an enrollment of 181 participants.
Intervention
Participants received a single Menactra® dose in this study. The study examined participants who had received one or two Menactra® doses in Study MTA26, as well as participants with no previous Menactra® vaccination.
Comparator
The groups differed by previous vaccination history: one prior dose, two prior doses, or no prior Menactra® vaccination. Allocation was non-randomized, so the groups should not be treated as equivalent randomized comparison arms.
Primary question
What proportion of participants had serum bactericidal antibody titers at or above the specified thresholds for serogroups A, C, Y, and W-135 before vaccination and 30 days after a single dose? The study also aimed to describe antibody persistence after earlier vaccination and the safety profile of a single dose.
The endpoint focuses on antibody measurements rather than a direct count of meningococcal disease cases. It therefore addresses whether measured antibody levels met prespecified titers at two time points: Day 0, before vaccination, and Day 30 after vaccination. The registry defines persistence using pre-vaccination titers and booster response using post-vaccination titers.
The central comparison is descriptive: how the measured antibody status differed across groups with different prior Menactra® histories. Because the study was non-randomized, any group differences could reflect differences between participants as well as vaccination history. The registry record does not report the endpoint percentages, group-specific antibody results, or statistical comparisons. Consequently, the posted record identifies the question and measurement approach but does not establish the size or precision of any observed antibody response.
3. Trial Design
This was a Phase 2, parallel-group study with non-randomized allocation and no masking. The registry lists the study as completed, with enrollment of 181. The study start is recorded as 2008-06 and primary completion as 2009-02. The sponsor was Sanofi Pasteur, a Sanofi Company.
Participants were divided according to prior Menactra® vaccination history. The One-Dose Menactra Group had received one dose in Study MTA26; the Two-Dose Menactra Group had received two doses in that study; and the Menactra vaccine-naïve Group had never received Menactra®. Participants received a single dose in the current study, for assessment of antibody response and safety.
The study objectives included assessing antibody persistence approximately three years after earlier vaccination, describing antibody responses after a single dose among participants with different prior vaccination histories, and describing safety after that dose. The primary endpoint description specifies assessment at Day 0 and Day 30 post-vaccination. The antibody measurements were made for meningococcal serogroups A, C, Y, and W-135 using a serum bactericidal assay with human complement.
Non-randomized allocation means that vaccination-history groups were not formed by random assignment in this study. Prior exposure defines group membership, so the design can describe patterns across those groups but does not provide the protection against confounding associated with randomized allocation. The registry record does not report further details of recruitment, eligibility criteria, masking procedures beyond the absence of masking, or a statistical analysis plan. It also does not report a sample-size justification.
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 181 participants who met all inclusion criteria and none of the exclusion criteria were enrolled and vaccinated.
Overall Study
| Stage | One-Dose Menactra Group | Two-Dose Menactra Group | Menactra-naïve Group |
|---|---|---|---|
| STARTED | 48 | 66 | 67 |
| COMPLETED | 47 | 66 | 65 |
| NOT COMPLETED | 1 | 0 | 2 |
Reasons for not completing this period:
| Reason | One-Dose Menactra Group | Two-Dose Menactra Group | Menactra-naïve Group |
|---|---|---|---|
| Protocol Violation | 1 | 0 | 1 |
| Withdrawal by Subject | 0 | 0 | 1 |
Analysis population for the primary outcome, as defined in the registry: Meningococcal serogroups A, C, Y, and W-135 antibody persistence and booster response were assessed in the Per-Protocol Analysis Set.
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.
| Characteristic | Unit | One-Dose Menactra Group | Two-Dose Menactra Group | Menactra-naïve Group | Total |
|---|---|---|---|---|---|
| Participants analysed | 48 | 66 | 67 | 181 | |
| Age, Categorical: <=18 years | Participants | 48 | 66 | 67 | 181 |
| Age, Categorical: Between 18 and 65 years | Participants | 0 | 0 | 0 | 0 |
| Age, Categorical: >=65 years | Participants | 0 | 0 | 0 | 0 |
| Age, Continuous | Months | 57.4 (SD 2.89) | 51.6 (SD 1.96) | 52.5 (SD 11.8) | 53.4 (SD 7.75) |
| Sex: Female, Male: Female | Participants | 20 | 38 | 22 | 80 |
| Sex: Female, Male: Male | Participants | 28 | 28 | 45 | 101 |
| Region of Enrollment: United States | Participants | 48 | 66 | 67 | 181 |
6. Primary Endpoint
The registry lists the primary outcome as Percentage of Participants With Serum Meningococcal Serogroups A, C, Y, and W-135 Bactericidal Antibody Titers ≥ 1:4 and ≥ 1:8 Before and Following Vaccination With Menactra®, measured over Day 0 (pre-vaccination) and Day 30 post-vaccination.
| Element | Registry entry |
|---|---|
| Result type | Number |
| Measure of spread | not applicable |
| Unit | Percentage of participants |
| Endpoint classification | Binary Endpoint |
The primary endpoint is the percentage of participants with serum meningococcal bactericidal antibody titers at or above 1:4 and 1:8 for serogroups A, C, Y, and W-135. Measurements were specified before vaccination on Day 0 and 30 days after vaccination. The endpoint is therefore a binary summary at each threshold: each participant’s titer either meets the threshold or does not, and the group result is expressed as a percentage of participants meeting it.
The assay was a serum bactericidal assay using human complement, abbreviated SBA-HC in the registry record. The record defines antibody persistence by pre-vaccination titers at or above 1:4 and 1:8. It defines booster response by titers at or above those same thresholds 30 days after the single Menactra® dose. Considering two thresholds provides descriptions of the proportion meeting each specified level, rather than only one cutoff.
In general, antibody titers are used as laboratory measures of an immune response. A percentage above a threshold is an interpretable way to describe how many participants met a defined assay criterion. It is not itself a count of clinical meningitis or meningococcemia cases. The registry record does not report the percentages or participant-level results, so the actual endpoint values and their uncertainty cannot be described from the posted results.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record establishes the design, study groups, measurement method, time points, and endpoint definitions. It does not report the group-specific percentages of participants whose antibody titers met the 1:4 or 1:8 thresholds. No numerical results for the primary antibody endpoint are included in the posted record, and no confidence intervals or hypothesis-test results are reported. Accordingly, the record does not support a quantitative description of antibody persistence or the size of the response after vaccination.
The study’s group structure is informative for understanding its question: participants with one prior dose and participants with two prior doses were considered separately from participants who had never received Menactra®. But this is not a randomized comparison. A difference among groups, if reported, would be an association across histories and could not automatically be attributed to the prior dose count. The registry record does not provide adjusted comparisons or information about potential differences between groups beyond the description that the naïve group was age-matched.
The endpoint uses threshold-based percentages. Such percentages summarize whether participants meet a defined antibody criterion, but they do not show the full distribution of titers. Results at the 1:4 and 1:8 cutoffs may describe different degrees of threshold attainment; without the recorded values, neither the number meeting either cutoff nor the pattern across serogroups can be stated. The record also does not report separate quantitative results by serogroup, despite specifying all four serogroups in the endpoint.
The safety data list no serious adverse events in the at-risk counts for any of the three groups. Other adverse events are reported for the groups, but the registry record does not supply event terms or establish whether these events were related to vaccination. Death counts are not reported. These entries should be read as registry safety counts, not as a complete account of every possible adverse event or as evidence about comparative safety.
Overall, the posted information supports a description of what the investigators intended to measure and how the groups were defined. It does not provide the numerical primary endpoint results needed to estimate the observed antibody proportions, compare groups, or assess precision. The record’s stated objectives should therefore be distinguished from reported findings: objectives describe the questions planned for assessment, whereas the available results do not quantify the answers.
9. Statistical Methods Explained
In general, a binary percentage endpoint classifies each participant according to whether an outcome criterion is met. Here the criterion is an antibody titer at or above a stated threshold. The percentage communicates the share of participants meeting that criterion, while the denominator is the number of participants assessed for that endpoint. The registry identifies the Per-Protocol Analysis Set as the population used for antibody persistence and booster response. It does not report the endpoint denominators or percentages, so the group-level estimates cannot be reconstructed from the record.
What does a threshold-based antibody endpoint represent?
In general, converting a continuous measurement into a threshold outcome makes the result easier to express as the proportion meeting a defined criterion. It also discards information about how far individual measurements lie above or below the cutoff. Two groups could have similar percentages at a particular threshold while having different underlying titer distributions, or different percentages while having measurements clustered near that threshold. The registry record defines two cutoffs, 1:4 and 1:8, and specifies four serogroups. It does not provide the underlying titer distributions or the resulting percentages for these thresholds.
The endpoint distinguishes pre-vaccination status from the post-vaccination measurement. The registry calls pre-vaccination threshold attainment persistence and defines booster response by threshold attainment on Day 30. These definitions indicate how the outcomes were categorized; they do not by themselves demonstrate that a participant’s titer increased. A before-and-after change requires paired values or a specified change measure, neither of which is reported in the registry record.
Why does non-randomized allocation matter?
In general, random allocation helps balance measured and unmeasured participant characteristics across treatment groups, on average. With non-randomized group formation, characteristics associated with previous vaccination can also differ across groups and influence outcomes. In this study, the groups were defined by previous Menactra® exposure. Thus, comparisons across the one-dose, two-dose, and naïve groups are descriptive unless a suitable analysis addresses confounding. The registry record does not report an adjusted analysis, covariate set, or statistical model, and it does not provide inferential comparisons.
The parallel-group structure means the study considered distinct groups during the current study period. The absence of masking is also reported. In general, masking can reduce the influence of knowledge about group assignment on some aspects of study conduct or assessment. The registry record does not describe a masking procedure, consistent with its designation of no masking. Since the endpoint is a laboratory measurement, the record alone does not establish whether laboratory personnel were blinded.
How should uncertainty be assessed?
In general, a confidence interval describes the range of estimates compatible with the data under a statistical procedure and its assumptions. It helps convey precision, which a point estimate alone cannot show. For a percentage, precision depends in part on the number of participants assessed and on the observed proportion. The record does not report confidence intervals, endpoint denominators, or endpoint percentages. Therefore, neither the magnitude nor precision of the antibody estimates can be evaluated from the posted results.
In general, a p-value assesses the compatibility of data with a specified null hypothesis under a model; it is not a measure of effect size or clinical importance. No p-values or hypothesis tests for antibody outcomes are reported. The registry record also does not report whether the intended analysis was descriptive or inferential beyond the stated objectives to assess persistence and describe response.
What does the stated analysis population imply?
The Per-Protocol Analysis Set is the population identified for antibody outcomes. In general, a per-protocol analysis includes participants meeting specified study requirements, but the exact rules depend on the protocol. The registry record does not report the membership rules, exclusions, or numbers included in this set. It is therefore not possible to assess how the analysis population differed from all enrolled participants or whether exclusions could affect interpretation.
Sample-size calculations and power are design concepts, not substitutes for observed results. In general, a planning calculation depends on assumptions about the effect to detect, allocation, significance level, and statistical method. The registry record does not report the trial’s own sample-size justification or statistical plan. Any planning illustration associated with the study should not be interpreted as observed power or as evidence that the study detected an effect. The actual endpoint findings and their uncertainty would be needed to assess what the study observed.
10. Multiplicity, Missing Data and Analysis Populations
The primary endpoint covers four serogroups and two antibody thresholds, measured at two time points. Considering multiple outcomes can raise multiplicity questions when formal hypothesis tests are conducted. In general, testing several hypotheses without an adjustment can increase the chance of at least one false-positive result. Whether that concern applies, and how it should be handled, depends on the planned estimands and analysis strategy.
The registry record does not report a multiplicity adjustment, a testing hierarchy, or a statistical analysis plan specifying how the serogroups, thresholds, time points, or groups would be handled. It also does not report inferential test results. It is therefore not possible to determine whether formal multiplicity control was planned or used. The endpoint description alone does not establish that each listed measure was treated as a separate confirmatory hypothesis.
Missing-data methods are also not reported in the registry record. The record does not describe missing antibody measurements, reasons for missingness, imputation, or sensitivity analyses. Without those details and the endpoint denominators, the impact of incomplete measurements cannot be assessed. The named Per-Protocol Analysis Set indicates the population designated for antibody outcomes, but its inclusion and exclusion rules and size are not reported.
These omissions limit assessment of how analyses were selected and how robust the endpoint summaries might be to missing observations. They do not establish that multiplicity or missing-data problems occurred; they mean the registry record does not describe how those issues were handled.
11. Safety Results
The registry reports serious adverse events as affected participants divided by participants at risk.
| Arm | Participants with serious adverse events | Participants at risk | Percentage |
|---|---|---|---|
| One-Dose Menactra Group | 0 | 48 | 0.0% |
| Two-Dose Menactra Group | 0 | 66 | 0.0% |
| Menactra-naïve Group | 0 | 67 | 0.0% |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 5.00% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| One-Dose Menactra Group | 26 of 48 |
| Two-Dose Menactra Group | 43 of 66 |
| Menactra-naïve Group | 41 of 67 |
Most frequent non-serious adverse event terms
| Event term | Organ system | One-Dose Menactra Group | Two-Dose Menactra Group | Menactra-naïve Group |
|---|---|---|---|---|
| Injection-site Pain | General disorders | 26 of 47 | 43 of 66 | 41 of 65 |
| Injection-site Erythema | General disorders | 11 of 47 | 26 of 66 | 25 of 65 |
| Irritability | Psychiatric disorders | 9 of 47 | 20 of 66 | 22 of 65 |
| Injection-site Swelling | General disorders | 9 of 47 | 20 of 66 | 21 of 65 |
| Drowsiness | Nervous system disorders | 9 of 47 | 16 of 66 | 7 of 65 |
| Arthralgia | Musculoskeletal and connective tissue disorders | 4 of 47 | 9 of 66 | 11 of 65 |
| Anorexia | Metabolism and nutrition disorders | 2 of 47 | 8 of 66 | 12 of 65 |
| Diarrhea | Gastrointestinal disorders | 4 of 47 | 7 of 66 | 6 of 65 |
| Headache | Nervous system disorders | 4 of 47 | 7 of 66 | 4 of 65 |
| Fever | General disorders | 6 of 47 | 4 of 66 | 3 of 65 |
The registry safety counts give the number at risk and the number affected for serious and other adverse events in each group. For serious adverse events, the counts are 0 of 48 in the One-Dose Menactra Group, 0 of 66 in the Two-Dose Menactra Group, and 0 of 67 in the Menactra-naïve Group. The record does not report deaths for these groups.
For other adverse events, the registry lists 26 of 48 participants in the One-Dose Menactra Group, 43 of 66 in the Two-Dose Menactra Group, and 41 of 67 in the Menactra-naïve Group. These are counts of participants affected, not counts of individual events. No serious adverse event terms are listed among the top serious terms.
In general, a zero count in a study group means that no event was recorded in that group during the reported observation; it does not establish that the underlying risk is zero. The record does not give event-level descriptions, severity or relatedness for the other adverse events, or details of the safety observation period. Since the groups were not randomized, the counts should not be read as a controlled comparison of safety between prior-vaccination histories.
12. What the Result Does, and Does Not, Mean
The registry record documents a study designed to assess persistence of antibodies and response after a single Menactra® dose among participants with different histories of prior vaccination. It specifies the assay, serogroups, thresholds, time points, and analysis population. It also reports group-level safety counts. These registry entries describe the intended measurements and some safety observations, but they do not include the numerical results for the primary antibody endpoint.
Without the endpoint percentages, the record cannot show how many participants met either threshold, how those proportions differed across groups, or how results varied by serogroup. Because no confidence intervals or inferential comparisons are reported, the precision of the antibody findings and the statistical uncertainty around group differences are also unavailable. The absence of a reported result should not be mistaken for a zero response or for no difference.
The non-randomized design further limits causal interpretation. Prior vaccination history defined the groups, rather than random allocation in this study. Any difference in antibody measures across groups could reflect prior vaccination, other differences between the groups, or both. The registry record does not report adjusted comparisons that would clarify this issue.
The safety counts indicate that no serious adverse events were recorded in the listed at-risk groups, while other adverse events affected participants in each group. Those counts alone do not establish causal attribution or comparative safety, and the registry record does not report deaths. They are also not a substitute for the missing antibody outcome results.
In short, the available record supports a careful description of the design and outcome definitions, but not a conclusion about the magnitude or precision of the antibody persistence or booster response. It does not establish clinical protection against meningitis or meningococcemia, because the primary endpoint is an antibody measure and clinical disease outcomes are not reported as results.
13. Why This Trial Matters Statistically
This study raises several useful statistical issues in a compact setting. First, its main outcome is a threshold-based percentage derived from laboratory measurements. Readers need to distinguish the proportion meeting a cutoff from the full distribution of antibody titers and from a direct clinical outcome. The endpoint’s two thresholds and four serogroups make clear why the definition of the outcome matters to interpretation.
Second, the study compares groups defined by prior vaccination history without randomized allocation. This design can describe patterns in antibody persistence and post-dose measurements, but it does not make the groups exchangeable. A descriptive difference is not, on its own, a causal estimate of the effect of one versus two prior doses or of prior vaccination versus no prior vaccination.
Third, the registry record illustrates the difference between a detailed endpoint definition and a report of endpoint findings. The record specifies when measurements were made, what assay was used, and how persistence and booster response were defined. Yet the actual percentages and uncertainty measures are not reported. Without those values, the central quantitative question remains unanswered in the posted record.
Finally, safety counts require attention to denominators and event definitions. The record distinguishes serious adverse events from other adverse events and gives at-risk group counts, but it does not report event details or deaths. Reading these entries descriptively avoids overstating what small-group safety summaries can establish. Together, these features make the study a useful example of how design, outcome construction, analysis reporting, and the limits of registry data shape statistical interpretation.
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 principal limitation for interpreting the antibody endpoint is that the registry record does not report the endpoint percentages, confidence intervals, or hypothesis-test results. It therefore does not permit quantitative assessment of the primary outcome, its precision, or differences across prior-vaccination groups. Although the objective and measurement plan are described, the posted results do not provide the numerical findings needed to answer the stated antibody questions.
The non-randomized allocation limits causal interpretation of differences between groups. Participants were grouped according to their earlier Menactra® exposure, and the registry provides no adjusted analysis or details on potential confounders. Age matching is noted for the vaccine-naïve participants, but the record does not provide further information about matching or balance across other characteristics.
The registry identifies the Per-Protocol Analysis Set but does not report its size, membership rules, exclusions, or relationship to the 181 enrolled participants. Missing-data handling is not reported. The record also does not describe a multiplicity strategy for the several serogroups, thresholds, time points, and groups involved in the endpoint.
Safety reporting is limited to counts of participants affected by serious and other adverse events. The record does not report deaths, detailed adverse-event terms, event severity or relatedness, or the safety observation period. The absence of recorded serious events in the listed groups does not establish that the risk was zero.
Finally, the registry record does not report the statistical analysis plan, sample-size justification, or further details on outcome-analysis methods. These limitations concern what can be assessed from the registry record and should not be taken as evidence that particular procedures were or were not used outside the information reported.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Antibody Persistence and Booster Dose Response in Subjects Who Received Menactra® Three Years Earlier in Study MTA26 — NCT00700713.
- Registry record last updated 2016-02-15; status last verified 2016-01.
- Results first posted 2016-02-15.
- 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.
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18. Record Summary
This completed Phase 2 study examined antibody persistence and response after a single Menactra® dose among participants with one prior dose, two prior doses, or no prior Menactra® vaccination. It was non-randomized, parallel-group, and unmasked, with enrollment of 181.
The primary endpoint concerned the percentage meeting serum bactericidal antibody titer thresholds of 1:4 and 1:8 for serogroups A, C, Y, and W-135 at Day 0 and Day 30 post-vaccination. Antibody outcomes were assessed in the Per-Protocol Analysis Set. The registry record does not report the endpoint percentages or inferential results.
No serious adverse events were recorded in the group counts. Other adverse events affected participants in all three groups; deaths are not reported. The non-randomized design and lack of reported antibody results limit comparative and causal interpretation.