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 Immunogenicity and Safety of Booster Dose of BoostrixTM Polio Vaccine in Previously Boosted Adults (NCT01323959), a non-randomized phase 4 study. The primary outcome is Number of Seroprotected Subjects Against Diphteria (D) and Tetanus (T) Antigens.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT01323959 |
| Phase | Phase 4 |
| Condition | Acellular Pertussis, Poliomyelitis, Diphtheria |
| Allocation | Non-Randomized |
| Design model | Parallel |
| Masking | None (open label) |
| Enrollment | 212 |
| Arms in the primary outcome | n/a |
| Lead sponsor | GlaxoSmithKline |
| Results posted | Yes |
2. Clinical Question
Population
Healthy adults who had received a booster vaccination in the earlier NCT01277705 study. The registry describes three groups according to the vaccine or vaccines received in that earlier study. The primary analysis population was the According-To-Protocol cohort for immunogenicity; further details about the cohort are not reported in the registry record.
Intervention
One additional dose of Boostrix Polio, given as an intramuscular injection into the deltoid region of the left arm. The study assessed immune responses and safety after this booster.
Comparator
There was no randomized comparator. All three groups received Boostrix Polio in this study, while their earlier booster vaccination histories differed: Boostrix Polio, co-administered Boostrix and Poliorix, or Revaxis. The registry cautions that these are not like-for-like control groups.
Primary question
At Month 1, how many subjects in the immunogenicity analysis cohort met the registry definition of seroprotection against both diphtheria and tetanus? A subject met that definition with anti-diphtheria and anti-tetanus antibody concentrations at least 0.1 international units per millilitre. The endpoint result is not reported in the registry record.
The broader study description also asks about persistence of immune responses ten years after an earlier booster and the immunogenicity and safety of another Boostrix Polio dose. The listed secondary outcomes cover booster responses and antibody measurements for pertussis, diphtheria, tetanus and polio, alongside symptom and adverse-event counts. Those aims provide context, but the available record details do not give the results for these outcomes. The study therefore poses an immunogenicity and safety question in previously boosted adults; it does not describe a randomized comparison of the current vaccine against an untreated or alternative-vaccine control group.
3. Trial Design
This was a Phase 4, non-randomized, unmasked, parallel-group study sponsored by GlaxoSmithKline. The registry lists enrollment of 212 and a completed status. The recorded study start was 2011-04-01, and primary completion was 2012-03-01. The study concerned healthy adults and evaluated a further Boostrix Polio booster after an earlier booster vaccination.
The groups were formed according to the prior study vaccination history. Subjects in the Boostrix Polio Group had received Boostrix Polio in NCT01277705. Those in the Boostrix+Poliorix Group had received co-administered Boostrix and Poliorix, while those in the Revaxis Group had received Revaxis. In the present study, each group received a dose of Boostrix Polio by intramuscular injection in the left deltoid region. Thus, the group labels distinguish prior histories rather than different current-study treatments.
Because allocation was not randomized and there was no masking, the groups should not be read as randomized treatment and control arms. The registry specifically cautions that they are not a like-for-like control comparison. Any differences between groups could reflect differences associated with their earlier vaccination histories or other group characteristics; the record does not report an adjustment strategy that would resolve such differences.
The primary endpoint was assessed at Month 1 in the According-To-Protocol cohort for immunogenicity. The record says this cohort included subjects who met eligibility criteria, complied with protocol procedures, received the booster, and had immunogenicity data. The rest of the population description is truncated in the registry record, so further inclusion details are not reported. The statistical analysis plan, allocation process beyond the non-randomized designation, and any planned interim analyses 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.
Before assignment: Out of the 212 subjects enrolled, 1 subject number was allocated without the study vaccine being administered to that subject, therefore the total number of subjects was 211.
Overall Study
| Stage | Boostrix Polio Group | Boostrix+Poliorix Group | Revaxis Group |
|---|---|---|---|
| STARTED | 67 | 72 | 72 |
| COMPLETED | 67 | 72 | 72 |
| NOT COMPLETED | 0 | 0 | 0 |
Analysis population for the primary outcome, as defined in the registry: The analysis was performed on the According-To-Protocol (ATP) cohort for immunogenicity, which included subjects who met all eligibility criteria, complied with the procedures defined in the protocol, who received the booster dose of Boostrix™ Polio vaccine and for whom data concerning immunogenicity outcome measures were available.
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 | Boostrix Polio Group | Boostrix+Poliorix Group | Revaxis Group | Total |
|---|---|---|---|---|---|
| Participants analysed | 67 | 72 | 72 | 211 | |
| Age, Continuous | Years | 50.4 (SD 12.82) | 49.2 (SD 12.53) | 51.4 (SD 13.06) | 50.33 (SD 12.78) |
| Sex: Female, Male: Female | Participants | 35 | 47 | 39 | 121 |
| Sex: Female, Male: Male | Participants | 32 | 25 | 33 | 90 |
6. Primary Endpoint
The registry lists the primary outcome as Number of Seroprotected Subjects Against Diphteria (D) and Tetanus (T) Antigens, measured over At Month 1.
| Element | Registry entry |
|---|---|
| Result type | Number |
| Measure of spread | not applicable |
| Unit | Subjects |
| Endpoint classification | Binary Endpoint |
The primary endpoint is the number of subjects seroprotected against both diphtheria and tetanus antigens at Month 1. The registry defines a seroprotected subject as a vaccinated subject whose anti-diphtheria and anti-tetanus antibody concentrations are each at least 0.1 international units per millilitre. The endpoint is therefore a binary classification at the subject level: each person either meets the stated combined threshold or does not. The endpoint itself is expressed as a count of subjects.
Antibody measurements provide a way to describe immune responses after vaccination. A prespecified threshold turns continuous concentration measurements into an interpretable category, while the combined diphtheria-and-tetanus definition requires the subject to meet the criterion for both antigens. This can be useful for reporting the proportion or count meeting a threshold, but it does not convey the full distribution of antibody concentrations. A count alone also does not show how far individual measurements lie above or below the threshold.
The endpoint is defined for the According-To-Protocol cohort for immunogenicity and is assessed at Month 1. The registry record does not report the observed count, group-specific endpoint results, uncertainty intervals, or a comparison estimate. It therefore supports a description of what was intended to be measured, but not a conclusion about the observed level of seroprotection.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The record identifies the study question, endpoint definition, study groups, and selected safety counts, but it does not report the primary endpoint result. No group-specific count of subjects meeting the combined diphtheria and tetanus seroprotection definition is available in the registry record. Nor are estimates of differences between groups, confidence intervals, or p-values reported. The key immunogenicity question therefore cannot be answered from the record details.
The group structure also limits comparative interpretation. All groups received Boostrix Polio in the current study, and their earlier vaccine histories differed. Since allocation was non-randomized, the groups cannot be treated as exchangeable by design. A contrast between them, if reported elsewhere, would not automatically isolate an effect of the earlier vaccine history or establish a causal difference. The registry explicitly cautions against treating the arms as a like-for-like control comparison.
The safety figures list zero serious adverse events in each group, with 67, 72, and 72 subjects respectively in the safety denominators. These are observed counts in the registry record, not proof that serious events cannot occur. Counts of zero describe what was recorded in the reported groups; without further information on follow-up, ascertainment, and uncertainty, they cannot quantify the range of possible event rates. Death counts are not reported in the registry record.
The record also lists other adverse-event counts of 52, 54, and 54 in the three groups, with the corresponding denominators of 67, 72, and 72. The meaning and classification details for those counts are not described in the registry record, so they should not be assigned a more specific interpretation. The record lists secondary outcomes involving local and general symptoms, unsolicited adverse events, and multiple antibody measures, but their results are not reported in the registry record.
In general, an estimate is more informative when accompanied by an uncertainty interval and a clear definition of the analysis population. An interval indicates the precision compatible with the data and analysis; a point estimate alone cannot show that precision. Neither endpoint estimates nor such intervals are reported for the primary outcome in this registry record. Consequently, interpretation should remain at the level of study design and recorded counts, not conclusions about comparative immunogenicity or safety.
9. Statistical Methods Explained
The registry describes a binary primary outcome, even though it reports the outcome concept as a number of subjects. The underlying classification is whether each subject met the joint antibody threshold for diphtheria and tetanus at Month 1. For a binary outcome, common summaries include the number meeting the criterion and the number assessed, with a proportion sometimes used to express frequency. The registry record does not report the primary outcome counts or proportions, so no numerical summary can be interpreted.
What does the endpoint threshold mean?
The stated threshold converts antibody concentrations into a category. This is useful when the scientific question is framed around meeting a specified level rather than comparing average concentrations. However, categorization discards information: subjects just above and well above the threshold are counted in the same category, while subjects just below it are grouped together despite potentially different concentrations. The secondary outcomes include antibody concentrations and titers, which address measurement scales beyond the primary binary classification, but their results are not reported in the registry record.
What can a confidence interval tell a reader?
General statistical context: a confidence interval describes the precision of an estimate under the assumptions of the method used. For a count or proportion, an interval can show that estimates based on limited observations may be compatible with a range of underlying values. It does not guarantee that the true value lies in the interval, and it does not correct bias caused by non-randomized group formation or missing data. No confidence interval for the primary endpoint is reported in the registry record.
What would a group comparison require?
General statistical context: a comparison of binary outcomes might be expressed as a difference in proportions or a ratio of proportions, accompanied by an uncertainty interval. The choice of measure and its interpretation depend on the scientific question and analysis plan. The registry record does not report a comparative estimate or identify a method used to estimate one. In this study, non-randomized allocation and differing prior vaccine histories are especially important: a numerical contrast would describe the observed groups, but would not by itself establish that the prior history caused any difference.
General statistical context: a p-value is a measure of how incompatible observed data are with a specified null hypothesis under a statistical model. It is not the probability that the null hypothesis is true, nor a measure of effect size or clinical importance. A p-value is not reported for the primary outcome in the registry record. The testing procedure, if any, is not reported in the registry record.
How should the planning illustration be read?
The registry’s planning assumptions describe an illustration based on the observed effect, not the trial’s own design. They specify 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. For non-time-to-event outcomes, the illustration is expressed as participants per arm for a chosen power level. These assumptions do not establish that the study was designed using this approach, and they are not observed power. The registry entries do not give the resulting planning values or the observed effect needed to interpret them.
General statistical context: planning calculations depend on assumptions about the effect size, variability or event frequency, allocation, significance level, and target power. A planning result is a conditional illustration: if the assumptions hold, it estimates the sample size needed under the chosen method. It does not describe the precision actually achieved after a study, and it cannot substitute for reporting the observed estimate and its uncertainty.
Why does over-dispersion matter?
General statistical context: over-dispersion occurs when observed variability is greater than a statistical model assumes. It can make standard errors too small if the model does not account for that extra variability, which may make intervals too narrow and tests too optimistic. This concept is more directly relevant to count models than to a simple binary classification, and the registry does not report a count-model analysis or an over-dispersion assessment for this endpoint. It should not be presumed to have been part of the study analysis.
The registry record does not report the statistical model, hypothesis tests, confidence-interval method, multiplicity procedure, missing-data approach, or sensitivity analyses. Those omissions prevent a fuller appraisal of how endpoint estimates would have been produced and how robust they might be. The primary endpoint definition and analysis cohort are available, but the numerical outcome and inferential methods are not reported in the registry record.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists 17 outcome measures and 6 analyses. The outcomes span several antibody measures and safety measures, including booster responses, concentrations or titers, local and general symptoms, and unsolicited adverse events. The record details do not identify which secondary outcomes were designated as confirmatory, how many tests were planned for each, or whether any adjustment for multiple testing was used. A multiplicity procedure is not reported in the registry record.
General statistical context: when many outcomes or comparisons are examined, the chance of at least one apparently unusual result can increase if each is assessed separately using the same threshold. Adjustment methods can address that issue, but may also change precision or the testing threshold. Without a stated analysis plan, the reader cannot determine whether or how multiplicity was handled. The primary endpoint result itself is not reported in the registry record.
The primary analysis population is described as the According-To-Protocol cohort for immunogenicity, including subjects meeting eligibility criteria, following protocol procedures, receiving the booster, and having immunogenicity data. The available description is truncated, and further criteria are not reported in the registry record. The numbers included in that primary analysis are not reported as endpoint denominators. The approach to missing antibody measurements, protocol deviations, or subjects excluded from the cohort is also not reported in the registry record.
General statistical context: an analysis restricted to participants with adequate protocol adherence and measurements may answer a different question from an analysis of everyone enrolled. Missing outcome data can affect both the estimated result and its precision, particularly if missingness is related to response or safety. A clear account of exclusions, missingness, and sensitivity analyses is needed to judge that possibility. Those details are not reported in the registry record.
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 |
|---|---|---|---|
| Boostrix Polio Group | 0 | 67 | 0.0% |
| Boostrix+Poliorix Group | 0 | 72 | 0.0% |
| Revaxis Group | 0 | 72 | 0.0% |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 5% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Boostrix Polio Group | 52 of 67 |
| Boostrix+Poliorix Group | 54 of 72 |
| Revaxis Group | 54 of 72 |
Most frequent non-serious adverse event terms
| Event term | Organ system | Boostrix Polio Group | Boostrix+Poliorix Group | Revaxis Group |
|---|---|---|---|---|
| Pain | General disorders | 42 of 67 | 49 of 72 | 46 of 72 |
| Redness | General disorders | 22 of 67 | 26 of 72 | 32 of 72 |
| Swelling | General disorders | 18 of 67 | 21 of 72 | 19 of 72 |
| Fatigue | General disorders | 12 of 65 | 16 of 71 | 15 of 71 |
| Headache | General disorders | 7 of 65 | 11 of 71 | 11 of 71 |
| Gastrointestinal symptom | General disorders | 7 of 65 | 9 of 71 | 4 of 71 |
The serious adverse-event figures list zero affected subjects in each group. The corresponding numbers at risk are 67 in the Boostrix Polio Group, 72 in the Boostrix+Poliorix Group, and 72 in the Revaxis Group. These are group-specific registry counts, and the groups are defined by prior vaccination history. They are not randomized treatment-control comparisons.
A recorded count of zero means no serious adverse event was listed for that group in these figures; it does not establish that the underlying risk is zero. Event counts are sensitive to the number followed and the duration and completeness of observation. Follow-up details for the safety figures are not reported in the registry record. Death counts are also not reported in the registry record, and no serious-event terms are listed.
The registry also gives other adverse-event counts of 52, 54, and 54 for the three groups. The classification and specific meaning of these figures are not reported in the registry record, so they should not be interpreted as a particular event category without that context. Overall, the serious-event figures are descriptive counts; they do not on their own establish comparative safety or exclude uncommon events.
12. What the Result Does, and Does Not, Mean
The record establishes that this completed Phase 4 study evaluated a further Boostrix Polio booster in healthy adults with different prior booster histories. Its primary endpoint was the number of subjects meeting the stated combined diphtheria and tetanus seroprotection threshold at Month 1. The record also identifies a broad set of secondary immunogenicity and safety outcomes. These details clarify what the study set out to measure.
The primary result is not reported in the registry record. Without the endpoint counts and analysis details, the record cannot show how many subjects met the seroprotection criterion, how estimates varied among groups, or how precisely any estimate was measured. It also cannot support a conclusion about whether responses differed according to prior vaccination history.
The study design does not support treating the three groups as randomized comparators. All received Boostrix Polio in the current study, and their earlier vaccination histories differed. Any group contrast would need to be interpreted with caution, even if numerical results were available, because non-randomized groups may differ for reasons other than the prior vaccine history. The registry itself warns that the arms are not a like-for-like control comparison.
The listed zero serious adverse-event counts describe the recorded observations for the groups. They do not prove that serious adverse events cannot occur, nor do they establish that risks are identical across groups. The other adverse-event counts lack enough classification detail in the registry entries to support a more specific interpretation.
General statistical context: a study result is best understood through the endpoint estimate, its uncertainty, the population analyzed, the handling of missing data, and the design used to make comparisons. The registry record contains some design and endpoint information but does not report the primary result or many analysis details. The appropriate conclusion is therefore limited: the study addressed a defined immunogenicity and safety question, while the available record details do not establish the magnitude or precision of the primary outcome.
13. Why This Trial Matters Statistically
This study is statistically notable because its groups share the current booster intervention but differ in earlier vaccination history. That arrangement can describe responses following a further booster across histories, but it is not equivalent to random assignment to competing current treatments. The distinction matters because the observed group differences, if any, could reflect characteristics linked to group membership rather than a causal effect of prior vaccination.
The primary endpoint also illustrates the trade-off involved in threshold-based outcomes. A seroprotection classification is straightforward to interpret against a defined antibody threshold, and the combined endpoint requires criteria for both diphtheria and tetanus. At the same time, a binary classification does not preserve the detail in the underlying antibody concentrations. The listed secondary antibody outcomes could provide complementary information, but their numerical results are not reported in the registry record.
The study’s stated focus on persistence ten years after an earlier booster and response to another booster raises questions about both prior immune response and subsequent response. However, the registry entries do not report results that quantify persistence or post-booster change. The design description and endpoints should not be mistaken for evidence of the size of either response.
Finally, the record demonstrates why endpoint definitions, analysis populations, and results must be considered together. The Month 1 endpoint has a clear threshold definition and a named protocol-based cohort, but its result, uncertainty, and detailed analysis methods are not reported. The serious-event counts are also descriptive rather than comparative evidence. These limits are central to any statistical reading of the study.
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 most important limitation for interpreting the registry record is that the primary endpoint result is not reported. The record defines seroprotection and names the Month 1 analysis population, but does not provide the number meeting the definition, the denominator analyzed, or uncertainty around the result. The listed secondary outcomes likewise lack reported results in the registry record.
The study was non-randomized and unmasked. Its groups were based on earlier vaccination histories, and all received Boostrix Polio in the current study. The registry cautions that the groups are not like-for-like controls. These design features limit causal interpretation of any between-group difference and make it inappropriate to frame the groups as randomized alternatives.
The description of the According-To-Protocol cohort is incomplete in the registry record. Further eligibility or analysis details, numbers excluded, and the handling of missing immunogenicity measurements are not reported. Without these details, the reader cannot assess how the analysis population relates to all enrolled subjects or whether exclusions could affect the results.
Details of statistical methods are also not reported: these include the model or test, interval estimation, multiplicity handling, and sensitivity analyses. The registry lists multiple outcome measures and analyses but does not explain how findings across them were interpreted. The safety figures provide serious-event counts and denominators, but the safety follow-up details and death counts are not reported. The classification for the other adverse-event counts is also not described in the registry entries.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Immunogenicity and Safety of Booster Dose of BoostrixTM Polio Vaccine in Previously Boosted Adults — NCT01323959.
- Registry record last updated 2018-06-06; status last verified 2017-04.
- Results first posted 2017-08-03.
- 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
NCT01323959 was a completed Phase 4, non-randomized, unmasked, parallel-group study sponsored by GlaxoSmithKline. It evaluated a Boostrix Polio booster in healthy adults whose earlier booster histories came from NCT01277705. The registry lists enrollment of 212, a start date of 2011-04-01, and primary completion on 2012-03-01.
The primary endpoint was the number of subjects seroprotected against diphtheria and tetanus at Month 1, defined using an antibody threshold of at least 0.1 international units per millilitre for both antigens. The record identifies an According-To-Protocol cohort for immunogenicity, but the primary endpoint result and further cohort details are not reported in the registry record.
The safety figures list zero serious adverse events in each group. Because the groups were non-randomized and differed in prior vaccination history, they are not like-for-like controls. The record does not report the primary result, comparative estimates, confidence intervals, or detailed statistical methods.