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 Safety of a Booster Dose of GlaxoSmithKline (GSK) Biologicals' Boostrix™ Vaccine in Healthy Vietnamese Children (NCT01988857), a na phase 3 study. The primary outcome is Numbers of Subjects With Any and Grade 3 Solicited Local Symptoms.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT01988857 |
| Phase | Phase 3 |
| Condition | Diphtheria, Tetanus, Acellular Pertussis |
| Allocation | Not applicable (single group) |
| Design model | Single Group |
| Masking | None (open label) |
| Enrollment | 302 |
| Arms in the primary outcome | n/a |
| Lead sponsor | GlaxoSmithKline |
| Results posted | Yes |
2. Clinical Question
Population
Healthy Vietnamese children aged 6-10 years were enrolled. The record lists an enrollment of 302 participants. The registry description identifies the study population as children receiving a booster dose; further eligibility details are not reported in the registry record.
Intervention
Participants received a single injection of GSK Biologicals’ combined reduced-antigen-content diphtheria-tetanus-acellular pertussis vaccine, Boostrix™. The registry identifies one study group, called the dTpa Group or Boostrix Group.
Comparator
No concurrent comparator group is identified. This is a single-group study, not a randomized comparison, so its results do not estimate a difference between Boostrix™ and another vaccine, placebo, or no vaccination.
Primary question
The primary endpoint concerns how many participants experienced any solicited local symptom, or a Grade 3 solicited local symptom, within 4 days (Days 0-3) after vaccination. The assessed symptoms were pain, redness, and swelling. Primary endpoint result counts are not reported in the registry record.
The study was designed to evaluate safety and reactogenicity after a single injection. Its registry summary also says that globally available data for the age group from four to six years of age would be used to bridge the age gap and support registration of the vaccine for children from the age of four years. That statement describes the stated rationale; it does not supply evidence about the present study’s symptom counts or establish how the age-bridging analysis was performed. The registry record does not report a comparison that could separate symptoms associated with vaccination from symptoms that might occur for other reasons.
3. Trial Design
This was a phase 3, completed, single-group study sponsored by GlaxoSmithKline. The registry reports an enrollment of 302 and identifies Boostrix™ as the sole intervention. Allocation is recorded as not applicable, and masking is recorded as none. These features are consistent with a study that followed one group rather than assigning participants at random to competing treatments. The record does not identify a control group.
The study evaluated a single injection of combined reduced-antigen-content diphtheria-tetanus-acellular pertussis vaccine in healthy Vietnamese children aged 6-10 years. The recorded study start was 2014-02-22, and primary completion was 2014-05-10. The status is completed. The record lists diphtheria, tetanus, and acellular pertussis as conditions.
The primary outcome concerns the count of participants with any and Grade 3 solicited local symptoms during the period within 4 days (Days 0-3) after vaccination. The record identifies four outcome measures overall, but the other outcome definitions and their results are not reported in the registry record. No analysis is listed in the registry results record.
Because there is only one study group, the design can describe observed outcomes among participants with available data, but it cannot provide a randomized treatment contrast. There is no like-for-like control comparison in the record. The number enrolled and the number included in the safety figures are not the same: enrollment is 302, while the safety denominator is 300. The reason for that difference is not reported in the registry record. Further protocol details, including eligibility criteria beyond the population description, 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: During the screening the following steps occurred: check for inclusion/exclusion criteria, contraindications/precautions, medical history of the subjects and signing informed consent forms.
Overall Study
| Stage | Boostrix Group |
|---|---|
| STARTED | 300 |
| COMPLETED | 300 |
| NOT COMPLETED | 0 |
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 Group |
|---|---|---|
| Participants analysed | 300 | |
| Age, Categorical: <=18 years | Participants | 300 |
| Age, Categorical: Between 18 and 65 years | Participants | 0 |
| Age, Categorical: >=65 years | Participants | 0 |
| Age, Continuous | Years | 7.9 (SD 1.38) |
| Sex: Female, Male: Female | Participants | 151 |
| Sex: Female, Male: Male | Participants | 149 |
| Race/Ethnicity, Customized: Asian - South East Asian Heritage | Participants | 300 |
6. Primary Endpoint
The registry lists the primary outcome as Numbers of Subjects With Any and Grade 3 Solicited Local Symptoms, measured over Within 4 days (Days 0-3) post vaccination period.
| Element | Registry entry |
|---|---|
| Result type | Count Of Participants |
| Measure of spread | not applicable |
| Unit | Participants |
| Endpoint classification | Binary Endpoint |
The primary endpoint counts participants with any and Grade 3 solicited local symptoms after vaccination. The symptoms assessed were pain, redness, and swelling at or around the injection site. “Any” means that the symptom occurred regardless of intensity grade. Grade 3 pain was defined as pain that prevented normal activity. Grade 3 redness or swelling was defined as redness or swelling spreading beyond 100 millimeters of the injection site. The observation period was within 4 days (Days 0-3) after vaccination.
Solicited symptoms are actively assessed rather than limited to events that participants happen to mention. As a general statistical concept, this approach can make the measurement of specified short-term symptoms more systematic, provided that the assessment procedure is applied consistently. A count of participants with a symptom is a binary-outcome summary at the participant level: each participant either meets the endpoint definition or does not. It is distinct from counting every symptom episode, and a participant may experience more than one symptom.
The endpoint is relevant to a safety and reactogenicity study because it records specified local experiences during a defined period after injection. However, the registry record does not report the primary endpoint counts, denominators, or an analysis estimate. It therefore does not allow a reader to quantify the frequency of any or Grade 3 local symptoms from the primary endpoint. The record also states that relationship analysis was not performed, so the endpoint description does not establish whether a symptom was judged related to vaccination.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record describes the question and endpoint, but does not report the primary endpoint results. In particular, counts of participants with any solicited local symptom and with Grade 3 solicited local symptoms are not reported in the registry record. No estimate, confidence interval, or hypothesis test for that endpoint is available in the posted results. The endpoint’s definition can therefore be explained, but the observed frequency and its precision cannot be assessed from the primary outcome information in this record.
The safety summary does contain a separate set of counts for the Boostrix Group. It reports 0 serious adverse events among 300 participants at risk, and 133 other adverse events among 300 participants at risk. These are descriptive counts. The record does not provide serious adverse event terms, and the top serious terms list is empty. The other adverse event count should not be substituted for the solicited local-symptom endpoint: the categories and assessment descriptions are different.
The enrollment count is 302, whereas the safety figures use 300 participants at risk. The reason for the difference is not reported in the registry record. Without an explanation of the analysis population and available follow-up, it is not possible to determine how participants outside the safety denominator were handled or whether missing outcome information affected the estimates.
As a general statistical principle, a confidence interval communicates uncertainty around an estimate; it does not guarantee that the underlying event rate lies within the interval. No confidence interval is posted for the primary endpoint or the adverse-event counts, so the precision of those rates cannot be judged. The design also has no concurrent control group, limiting interpretation to outcomes observed in the single group rather than a comparative treatment effect.
The record identifies the study as completed and states that relationship analysis was not performed for the primary endpoint. It does not report the detailed statistical analysis plan, an interim analysis plan, or analysis populations. Consequently, no claim about statistical significance, adjusted effects, or causation follows from the registry information. The data describe a study intended to assess safety and reactogenicity, but the posted primary endpoint results are insufficient to describe the frequency of the specified local symptoms.
9. Statistical Methods Explained
What kind of outcome is being counted? The primary outcome is a participant count for a binary event definition. Each participant can be classified according to whether any specified symptom occurred during the observation period, and separately according to whether a Grade 3 symptom occurred. These are distinct summaries: “any” includes symptoms regardless of intensity, while Grade 3 uses the severity definitions stated in the record. The endpoint counts participants, not the total number of symptom episodes. If a participant experienced several of the assessed symptoms, the participant-level count would still be about whether the endpoint criterion was met.
Why is the observation period important? The primary endpoint applies within 4 days (Days 0-3) after vaccination. A defined window makes clear which reports qualify for this endpoint and which do not. It also restricts what can be inferred: a short-term solicited symptom count does not describe events outside that window or every possible safety outcome. The registry record gives the window and symptom definitions, but the primary endpoint counts and denominators are not reported in the registry record.
What does a single-group study estimate? In general, a single-group study can describe the number or proportion of participants meeting an outcome definition in that group, when the relevant counts and denominator are available. It does not by itself estimate the difference that would have occurred under a different treatment or under no intervention. A concurrent control group can help distinguish outcomes associated with the intervention from background events and other influences. No such comparator is identified in this record, and the study is not a randomized comparison.
How should counts and rates be distinguished? A count is the number of participants meeting a definition. A rate or proportion relates that count to a specified denominator. The primary endpoint is described as a count of participants, but its results are absent. The separate safety figures include both counts and participants at risk: 0 serious adverse events among 300 at risk, and 133 other adverse events among 300 at risk. No further rates or comparisons are calculated in this interpretation. As a general matter, choosing the correct denominator is essential: enrollment, participants at risk, and participants with complete endpoint assessment may refer to different populations. The record does not explain why enrollment of 302 differs from the safety denominator of 300.
What does a confidence interval contribute? In general, an estimate based on a sample is subject to uncertainty because the observed participants are not necessarily identical to all participants who could meet the study criteria. A confidence interval presents a range of values compatible with the data under a statistical procedure and its assumptions. Its width conveys precision: wider intervals indicate less precise estimation, and narrower intervals indicate more precision. A confidence interval is not a guarantee about an individual participant’s outcome. The registry record does not report a confidence interval for the primary endpoint, so precision for that endpoint cannot be assessed.
What can a hypothesis test say? In general, a hypothesis test evaluates data relative to a specified null hypothesis and model assumptions. A p-value measures how unusual data at least as extreme as those observed would be under that null model; it is not the probability that the null hypothesis is true, nor does it measure clinical importance. The registry record lists no analyses, and no primary endpoint p-value is reported. Therefore, no statistical-significance conclusion can be drawn from the posted primary outcome information. The absence of a reported test is not evidence that an effect is absent.
How should planning illustrations be understood? Any sample-size planning illustrations use assumptions that differ from this study’s single-group design. The stated illustration assumes a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation, with the effect to detect expressed as a stated fraction of an observed effect. Those are planning assumptions, not a description of the study’s allocation or analysis. The record does not report its own sample-size justification. Planning sample sizes are hypothetical design calculations; they are not observed power and do not establish the probability that this completed study detected an effect.
Why do model assumptions matter? General statistical methods rely on assumptions about the data and sampling process. For binary outcomes, methods typically need a clearly defined event, denominator, and participant-level analysis. A model may also rely on assumptions about independence and how participants were selected or observed. Over-dispersion is a general concern when variation in counts exceeds what a chosen model expects; it is not automatically a feature of every binary endpoint. The registry record does not identify a statistical model, diagnostics, covariate adjustment, or method for handling repeated symptoms. No particular modeling approach should therefore be attributed to this study.
What do the posted analyses support? The registry record reports four outcome measures and no listed analyses. The primary outcome description is available, but its results are not. The safety summary gives the adverse-event counts and denominators, without an inferential comparison. A careful reading separates an outcome definition from an outcome result, and a descriptive count from a comparative or adjusted effect. Only the information actually recorded can support interpretation; additional analytic details are not reported in the registry record.
10. Multiplicity, Missing Data and Analysis Populations
The registry record lists four outcome measures, but only the primary outcome definition is described in the record details used for this interpretation. The other outcome definitions and results are not reported in the registry record. No analyses are listed, and no multiplicity procedure is reported. Multiplicity refers, in general, to the increased chance of at least one false-positive finding when several hypotheses are tested. Statistical plans may address it through prespecified outcome hierarchies, adjusted testing, or other approaches. None of those approaches can be attributed to this study from the available registry information.
Missing-data handling is also not reported in the registry record. The enrollment count is 302, while the safety figures use 300 participants at risk. The record does not say why these counts differ, whether the difference reflects missing assessments, or how participants without relevant data were treated. It also does not specify whether the primary endpoint denominator differs from the safety denominator. Those details matter because an outcome count is interpretable only in relation to the population assessed and the way unavailable observations are handled.
Analysis populations, such as an intention-to-treat population or a safety population, are not described for the primary endpoint. The terms should not be inferred from the fact that a safety denominator is listed. The registry record also does not report interim analyses, stopping rules, or a statistical analysis plan. These omissions prevent assessment of whether outcome selection, missing-data procedures, and analysis choices were prespecified. They do not establish that such procedures were absent from the full study documentation; they are simply 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 Group | 0 | 300 | 0.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Boostrix Group | 0 of 300 |
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 Group | 133 of 300 |
Most frequent non-serious adverse event terms
| Event term | Organ system | Boostrix Group |
|---|---|---|
| Pain | General disorders | 105 of 300 |
| Redness | General disorders | 55 of 300 |
| Fatigue | General disorders | 42 of 300 |
| Swelling | General disorders | 40 of 300 |
| Headache | General disorders | 33 of 300 |
| Gastrointestinal symptoms | General disorders | 15 of 300 |
The safety summary identifies one Boostrix Group and reports 0 serious adverse events among 300 participants at risk. It also reports 133 other adverse events among 300 participants at risk. These counts should be read as descriptive safety information, not as a comparison with another group. The record provides no top serious adverse event terms, and the reason that the safety denominator is 300 while enrollment is 302 is not reported in the registry record.
The count of serious adverse events is not the same measure as the primary endpoint. The primary endpoint covers solicited local symptoms—pain, redness, and swelling—within 4 days (Days 0-3), including a separate Grade 3 definition. The safety summary does not provide the primary endpoint results, and the 133 other adverse events should not be treated as a count of those solicited local symptoms.
As a general statistical point, a zero count in an observed group does not demonstrate that the underlying risk is zero. The ability to characterize uncommon events depends on the amount and completeness of observation, and the record does not provide a confidence interval or further detail about follow-up for these safety figures. The counts describe what was recorded in the registry summary; they do not alone establish comparative safety or causation.
12. What the Result Does, and Does Not, Mean
The registry record establishes that a completed phase 3 study evaluated a single Boostrix™ injection in healthy Vietnamese children aged 6-10 years, with a primary focus on solicited local symptoms within 4 days (Days 0-3). It also provides a separate safety summary with 0 serious adverse events among 300 participants at risk and 133 other adverse events among 300 participants at risk. These are the observations the record makes available for interpretation.
The primary endpoint results are not reported in the registry record. Without the counts and denominator for participants with any or Grade 3 local symptoms, the frequency of those outcomes cannot be described from this record. No confidence intervals or hypothesis tests for the primary endpoint are reported. It is therefore not possible to judge the precision of the primary endpoint estimate or to claim a statistically significant result from the posted information.
The single-group design also sets a boundary on interpretation. Observed outcomes can be described for the study group, but there is no concurrent control group for estimating how outcomes would differ under another intervention or without vaccination. The record does not report relationship analysis for the primary endpoint, so the endpoint counts, even if available, would not by themselves establish that vaccination caused each symptom.
The registry summary says global data for the age group from four to six years of age would be used to bridge the age gap and aid registration for children from the age of four years. That stated aim should be distinguished from evidence about the results in this study: the details and results of any age-bridging analysis are not reported in the registry record. Overall, the posted information supports a description of the study design and selected safety counts, but not a complete assessment of the primary symptom outcomes or comparative effects.
13. Why This Trial Matters Statistically
This study illustrates why a clearly defined endpoint and a posted result are both needed for statistical interpretation. The registry specifies the local symptoms, the Grade 3 thresholds, and the post-vaccination observation period. That detail tells readers what the primary outcome was intended to measure. However, because the primary counts and denominators are not reported in the registry record, the outcome definition cannot be converted into an estimate of how often participants experienced those symptoms.
It also illustrates the distinction between enrollment and an analysis denominator. The record lists 302 enrolled participants but uses 300 participants at risk for the safety figures. A denominator is not a minor detail: readers need to know which participants contributed data to each result and why. The reason for the difference is not reported in the registry record.
The single-group design is another key statistical feature. It can describe outcomes within the vaccinated group, but it cannot provide a randomized comparison with another treatment. This boundary matters whenever results are read as evidence about an intervention rather than as a description of recorded events. In addition, a zero count for serious adverse events is a finite study observation, not proof that an event cannot occur.
Finally, the record distinguishes study intent from available analysis. It describes safety and reactogenicity as aims and notes an age-bridging rationale, but does not post the primary endpoint results, analysis details, or age-bridging results. Careful statistical reading keeps those aims separate from the evidence that can be quantified from the registry record.
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 consequential limitation of the posted record is that the primary endpoint results are not reported. Although the endpoint is defined in detail, the counts and denominators for any and Grade 3 solicited local symptoms are unavailable. No estimate or precision measure can be assessed for the primary question.
The study is single-group and has no identified comparator. Its descriptive findings cannot estimate a randomized contrast or distinguish outcomes in the study group from what might have occurred under another condition. The record also states that relationship analysis was not performed for the primary endpoint, which limits interpretation of symptom counts as evidence of causation.
Enrollment is 302, while the safety denominator is 300; the reason for this difference is not reported in the registry record. Missing-data procedures and analysis populations are also not reported, so the handling of participants without available outcome information cannot be evaluated. The registry lists four outcome measures, but the other outcome definitions and results are not reported in the registry record. No analyses are listed, and details of the statistical plan, multiplicity handling, or interim analyses are not reported.
The serious adverse event summary gives a count of 0 among 300 at risk, but no confidence interval or event-term detail is available. A finite safety summary cannot characterize every possible event or establish comparative safety. The age-bridging aim is described, but the related analysis and results are not reported in the registry record. These limitations concern the information available in the registry record and do not establish what may be available in other study documentation.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Safety of a Booster Dose of GlaxoSmithKline (GSK) Biologicals' Boostrix™ Vaccine in Healthy Vietnamese Children — NCT01988857.
- Registry record last updated 2018-08-02; status last verified 2018-06.
- Results first posted 2016-12-12.
- 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 3 study evaluated a single injection of Boostrix™ in healthy Vietnamese children aged 6-10 years. It enrolled 302 participants and used a single-group design with no masking and no concurrent comparator. The primary endpoint counted participants with any and Grade 3 solicited local symptoms within 4 days (Days 0-3) after vaccination, including pain, redness, and swelling.
Primary endpoint results are not reported in the registry record, and no analyses are listed. The safety summary reports 0 serious adverse events and 133 other adverse events among 300 participants at risk. The difference between enrollment and the safety denominator is not explained in the registry record. The record describes an age-bridging rationale using global data, but does not report the details or results of that analysis.