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 Tdap Vaccine Safety for Plasma Donors (NCT04142983), a na phase 2, phase 3 study. The primary outcome is Number of Participants With Treatment Emergent Adverse Events (TEAEs).
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT04142983 |
| Phase | Phase 2, Phase 3 |
| Condition | Tetanus |
| Allocation | Not applicable (single group) |
| Design model | Single Group |
| Masking | None (open label) |
| Enrollment | 110 |
| Arms in the primary outcome | n/a |
| Lead sponsor | GCAM Inc. |
| Results posted | Yes |
2. Clinical Question
Population
The study concerned plasma donors eligible for study participation and plasmapheresis. The registry describes the safety population as enrolled participants who received at least one vaccination and had safety data. Enrollment was 110, but the adverse-event figures list 100 participants at risk; the registry record does not explain this difference in denominators. The results therefore need to be read in relation to the population specified for each measure, rather than treating enrollment as the denominator for every reported count.
Intervention
Participants received Adacel, a licensed Tdap vaccine. The study description specifies a dose every 3 months ±1 week, for a total of 5 immunizations over 12 months, with follow-up after the final vaccination. The principal safety question concerns treatment-emergent adverse events, defined as events occurring after the first study treatment. The registry also names anti-tetanus antibody titers and post-vaccination antibody-range levels as secondary outcomes.
Comparator
There was no comparison group. The registry lists a single-group model, no allocation, and no masking. The results can describe events recorded among participants receiving the study vaccination, but they do not provide a randomized contrast with another vaccine, placebo, or an unvaccinated group. Without such a contrast, observed events cannot be separated statistically from events that might have occurred over the same period for other reasons.
Primary question
The primary endpoint asks how many participants experienced treatment-emergent adverse events during the stated timeframe of up to 18 months. The registry defines serious treatment-emergent events separately by specified consequences, including death, life-threatening events, hospitalization, persistent or significant incapacity, or an important medical event requiring intervention to prevent such outcomes. The registry record does not report a distinct result for the primary endpoint itself.
3. Trial Design
This was a prospective, open-label, single-arm, multicenter study of Tdap vaccination in plasma donors. The registry lists the phases as Phase 2 and Phase 3, while the brief summary describes the study as Phase 1. That difference in phase descriptions is present in the registry record and is not resolved there. Allocation is listed as not applicable, and masking is listed as none; the design therefore does not support a randomized comparison between treatment arms.
The planned regimen was Adacel vaccination every 3 months ±1 week, for 5 immunizations over 12 months. The study description includes a 6 month follow-up after the last vaccination. Participants were to be assessed for adverse events, with plasma samples collected for antibody titers at specified intervals. Routine plasmapheresis and donor eligibility assessments were part of the donor program, while the summary says the study collected data specifically required for its objectives.
Enrollment was 110. The registry lists the study as completed, with a start date of 2020-02-03 and a primary completion date of 2021-11-03. The primary endpoint timeframe is up to 18 months. The record does not report the number of participants who completed all vaccinations or follow-up, nor does it describe how many discontinued or why.
A single-group design can describe what was observed in participants who received the study regimen, but it does not estimate a comparative treatment effect. Open-label status also means participants and study personnel were not masked, as recorded. Whether particular steps were used to reduce observation or reporting bias is not reported in the registry record. The study's stated focus was safety and antibody responses; the registry lists two secondary antibody outcomes, but it does not provide their results in the registry record for this analysis.
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: All participants were "Qualified Donors" who had been qualified for continued plasma donations in accordance with Donor Eligibility requirements found in 21 CFR 630.10 and 630.15, and Source Plasma regulations under 21 CRF 640, Subpart G. A total of 110 participants were consented and screened for eligibility. Ten of these did not meet eligibility criteria.
Overall Study
| Stage | Tdap Vaccine |
|---|---|
| STARTED | 110 |
| Treatment Population | 100 |
| COMPLETED | 11 |
| NOT COMPLETED | 99 |
Reasons for not completing this period:
| Reason | Tdap Vaccine |
|---|---|
| Lost to Follow-up | 73 |
| Withdrawal by Subject | 10 |
| Physician Decision | 1 |
| Adverse Event | 1 |
| No longer eligible | 4 |
| Screen Failure | 10 |
Analysis population for the primary outcome, as defined in the registry: Population included all enrolled participants who received at least one vaccination and had safety data.
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 | Tdap Vaccine |
|---|---|---|
| Participants analysed | 100 | |
| Age, Continuous | years | 38.2 (SD 9.17) |
| Sex: Female, Male: Female | Participants | 48 |
| Sex: Female, Male: Male | Participants | 52 |
| Ethnicity (NIH/OMB): Hispanic or Latino | Participants | 100 |
| Ethnicity (NIH/OMB): Not Hispanic or Latino | Participants | 0 |
| Ethnicity (NIH/OMB): Unknown or Not Reported | Participants | 0 |
| Race (NIH/OMB): American Indian or Alaska Native | Participants | 0 |
| Race (NIH/OMB): Asian | Participants | 0 |
| Race (NIH/OMB): Native Hawaiian or Other Pacific Islander | Participants | 0 |
| Race (NIH/OMB): Black or African American | Participants | 0 |
| Race (NIH/OMB): White | Participants | 100 |
| Race (NIH/OMB): More than one race | Participants | 0 |
| Race (NIH/OMB): Unknown or Not Reported | Participants | 0 |
| Region of Enrollment: United States | participants | 100 |
6. Primary Endpoint
The registry lists the primary outcome as Number of Participants With Treatment Emergent Adverse Events (TEAEs), measured over Up to 18 months.
| Element | Registry entry |
|---|---|
| Result type | Number |
| Measure of spread | not applicable |
| Unit | participants |
| Endpoint classification | Binary Endpoint |
The primary endpoint is the number of participants with treatment-emergent adverse events, with a timeframe of up to 18 months. A treatment-emergent event is defined as an adverse event occurring after the first study treatment. An adverse event is an untoward medical occurrence in a participant who received study drug, regardless of whether a causal relationship is considered possible. The endpoint is therefore based on events recorded after vaccination, not solely on events judged to have been caused by vaccination.
Counting participants with events is a binary-outcome approach at the participant level: each participant either has at least one event meeting the endpoint definition or does not. This can make the safety summary easier to interpret than a count of every event, particularly if one participant experiences multiple events. The registry definition does not, however, establish that all event types have equal clinical importance, or convey their duration, severity, or frequency within a participant.
The endpoint is used to characterize observed safety experience over the stated follow-up period. The registry record does not report a distinct primary-endpoint count or a confidence interval for that endpoint. The adverse-event listing reports 71 participants affected by other events among 100 at risk, but the record does not explicitly identify that figure as the primary endpoint result. It should not be substituted for a separately reported primary-endpoint result without that link being stated.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry describes a study intended to collect safety and antibody-response information from plasma donors receiving repeated Adacel vaccinations. Its design is descriptive: participants received the vaccine in a single group, without a randomized control group. Consequently, the posted event counts describe what was recorded among participants at risk in the study; they do not quantify how the event experience differs from a comparator group.
The adverse-event listing reports 0 participants with serious events among 100 at risk and 71 participants with other events among 100 at risk. It also reports 0 deaths. These are counts as recorded, not estimates of comparative risk. The registry record does not provide a confidence interval for these counts, details of event timing, or a breakdown of the other events by type or severity. The serious-event term listing is empty. The figure of 71 for other events should not be assumed to be the primary endpoint result, because the registry does not explicitly connect that adverse-event category to the primary endpoint definition.
The enrolled total is 110, whereas the adverse-event listing uses 100 as the number at risk. The record does not explain why those denominators differ. The primary endpoint population is described as enrolled participants who received at least one vaccination and had safety data, but the record does not give the count meeting that definition. Thus the relevant denominator and participant flow cannot be fully reconstructed from the posted information.
Three outcome measures are listed, including the primary safety endpoint and two secondary antibody outcomes. No analyses are listed. The record does not report antibody-titer values, the number of participants in antibody ranges, or inferential results for those outcomes. It also does not report the statistical analysis plan, confidence intervals, or any hypothesis-testing results. Absence of those results from the registry record is not evidence that an outcome was absent or that a particular statistical result was obtained.
General statistical interpretation: event counts from one group can describe frequency in that observed group, but they do not isolate the effect of an intervention from background events, selection into the study, or changes over time. A confidence interval would describe the uncertainty associated with an estimated quantity under a statistical model; no such interval is reported for the adverse-event figures in the registry record. Without uncertainty estimates and a comparison group, the counts have limited use for judging how precisely the observed experience represents other plasma donors or what would have occurred without vaccination.
The registry also includes sample-size planning assumptions based on detecting a fraction of an observed effect, with two-sided significance level 0.05, equal allocation between two arms, and a normal approximation. These are planning illustrations, not the stated design of this single-group study. The registry record does not report a trial-specific sample-size justification, and these assumptions should not be read as evidence that the trial had a two-arm comparison or a particular degree of power.
9. Statistical Methods Explained
The primary outcome is a participant-level event count: the number of participants who had treatment-emergent adverse events. In general, an endpoint of this kind converts a participant's event history into a yes-or-no classification for the stated period. That summary is different from counting all adverse-event episodes. If one participant has multiple events, a participant-level count would still count that person once, whereas an event-level total could count each episode. The registry identifies the endpoint as a number of participants, but does not provide detailed event-level results.
What does a single-group design estimate?
General explanation: a single-group safety summary describes the observed experience among participants receiving the intervention. It does not estimate a difference between treatment groups because there is no concurrently assigned control group. A randomized comparison can help distinguish differences associated with treatment assignment from differences due to participant characteristics or other influences. This study is listed as single group, with allocation not applicable and no masking, so a comparative treatment effect is not available from the design as described.
The study description says participants would be assessed for adverse events and followed after vaccination. The registry defines treatment-emergent events by timing after the first study treatment, while its definition of an adverse event does not require a causal relationship to be considered possible. Accordingly, treatment-emergent describes when an event occurred relative to treatment; it does not by itself establish that treatment caused it. Causal attribution rules or adjudication procedures beyond the registry definition are not reported in the registry record.
How should event counts and denominators be read?
The adverse-event information gives 100 participants at risk for serious events and 0 affected, and 100 at risk for other events and 71 affected. The record also reports 0 deaths. These figures should be read as category-specific counts, not as a comparison between groups. The enrolled total is 110, and the registry record does not explain the difference between that total and the 100 participants at risk shown in the adverse-event information. It also does not report whether participants with missing safety data were excluded, whether the denominator changes by event category, or how incomplete follow-up was handled.
General explanation: a count has meaning only in relation to the population and observation period to which its denominator applies. An at-risk denominator indicates the group considered eligible for the relevant event summary, but it does not necessarily equal the number enrolled or the number completing follow-up. If the denominator is smaller than enrollment, participant flow and missingness details help explain which observations contribute to the result. Those details are not reported in the registry record, so the reason for the denominator difference remains unknown.
What would uncertainty measures add?
General explanation: a confidence interval gives a range of values compatible with the observed data under a specified statistical method. For an event proportion, it conveys uncertainty arising from the finite number of observed participants. A confidence interval does not address all sources of uncertainty: it cannot remove bias from selection, incomplete follow-up, outcome measurement, or the lack of a comparator. The registry record does not report confidence intervals for the adverse-event figures, so their statistical precision cannot be assessed from an interval estimate.
General explanation: when event data are sparse, conventional approximations can be unreliable, and exact or otherwise suitable methods may be considered. The registry record does not identify a method for estimating uncertainty around the serious-event count. No method should be attributed to this study without a reported analysis plan or result.
What is the role of the antibody outcomes?
The registry lists anti-tetanus antibody titers over time and the number of participants with post-vaccination anti-tetanus antibody range levels as secondary outcomes. These are different kinds of measures: titers are intended to describe antibody measurements across time, while range levels classify participants according to antibody categories. The registry record does not provide the measurements, category thresholds, analysis methods, or results for these outcomes. It is therefore not possible to evaluate their numerical patterns or precision from the information recorded.
Repeated measurements can raise methodological questions about within-participant correlation, the timing of measurements, and incomplete follow-up. General explanation: measurements from the same participant are not necessarily statistically independent, so analyses of change over time often need to account for that dependence. The particular approach used for these antibody outcomes is not reported in the registry record. Nor is it reported how measurements taken at irregular times, if any, would be handled.
How do the planning assumptions relate to this study?
The registry states that sample-size planning illustrations use 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 fraction of the observed effect. It distinguishes participants per arm for ordinary outcomes from total events for time-to-event outcomes. These assumptions describe planning illustrations, not the conduct or analysis of this single-group trial. The record does not report the numerical illustration results or a trial-specific sample-size justification. The illustrations are not observed power and do not establish the precision of the posted safety counts.
General explanation: power is a design concept tied to a specified comparison, effect size, variability, and analysis. It is not a measure of whether a study has demonstrated an effect after data are collected. In this record, a two-arm planning framework does not match the listed single-group design. No trial-specific power calculation or statistical analysis plan is reported in the registry record, so neither should be inferred from the planning assumptions.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists three outcome measures: the primary treatment-emergent adverse-event count and two secondary antibody outcomes. It reports no analyses. A multiplicity strategy—such as a hierarchy for testing outcomes, an adjustment to control the chance of false-positive findings, or a distinction between confirmatory and exploratory analyses—is not reported in the registry record. Without reported analyses, there are no posted hypothesis tests to interpret as a family of statistical claims.
Missing-data methods are also not reported. The study description refers to repeated antibody sampling and follow-up, but the record does not state how missed visits, unavailable samples, early withdrawal, or incomplete adverse-event follow-up were handled. It does not report participant flow after enrollment or the number completing each assessment. The difference between enrollment of 110 and the adverse-event denominator of 100 is unexplained; it should not be attributed to a particular form of missingness or exclusion.
The primary endpoint population is defined as enrolled participants who received at least one vaccination and had safety data. The registry does not report the number meeting that definition, nor does it describe other analysis populations. The record therefore does not establish whether outcomes were analyzed in all enrolled participants, only vaccinated participants, or another defined set, beyond the stated safety-population description. Statistical methods for antibody outcomes, handling of repeated measurements, and sensitivity analyses are not reported in the registry record.
General explanation: multiplicity matters when several outcomes or comparisons are tested, because repeated testing can increase the chance of at least one false-positive result. Missing-data handling matters because analyses may depend on which observations are available and why others are absent. These are interpretive considerations, not claims about procedures used in this study.
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 |
|---|---|---|---|
| Tdap Vaccine | 0 | 100 | 0.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Tdap Vaccine | 0 of 100 |
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 |
|---|---|
| Tdap Vaccine | 71 of 100 |
Most frequent non-serious adverse event terms
| Event term | Organ system | Tdap Vaccine |
|---|---|---|
| Injection site pain | General disorders | 37 of 100 |
| Injection site bruising | General disorders | 26 of 100 |
| Red blood cells urine positive | Investigations | 18 of 100 |
| Urine leukocyte esterase positive | Investigations | 17 of 100 |
| Injection site erythema | General disorders | 14 of 100 |
| Protein urine present | Investigations | 14 of 100 |
| Hemoglobin urine present | Investigations | 11 of 100 |
| Injection site induration | General disorders | 8 of 100 |
| Glucose urine present | Investigations | 7 of 100 |
| Injection site swelling | General disorders | 6 of 100 |
The safety information lists 0 participants with serious events among 100 at risk, 71 participants with other events among 100 at risk, and 0 deaths. The registry defines serious events by specified outcomes or important medical events that may require intervention. The list of top serious-event terms is empty. These figures should be read as the recorded counts within the categories and denominators stated; they do not establish that no event of any kind occurred, because other events are separately listed.
The 71 other events are not broken down by type, severity, duration, or timing in the registry information available for this analysis. The record does not explicitly identify this count as the primary endpoint result, even though the primary endpoint concerns participants with treatment-emergent adverse events. The count therefore should not be relabeled as the primary result without a clear registry link between the categories.
The adverse-event denominator is 100, while enrollment is 110. The registry record does not explain the difference, and it does not state how incomplete follow-up or missing safety data were addressed. The figures describe observed events in the listed group; they do not provide a comparison with an unvaccinated group or another treatment. No confidence intervals are reported for these counts.
12. What the Result Does, and Does Not, Mean
The posted information establishes the broad design and the categories of results recorded for this study. It describes a prospective, open-label, single-group vaccination study in plasma donors and defines a primary safety outcome based on participants experiencing treatment-emergent adverse events. The adverse-event listing reports 0 serious events and 0 deaths among the stated group of 100 at risk, and 71 participants with other events among 100 at risk. These counts are descriptive observations from the registry record.
They do not, by themselves, establish whether events were caused by vaccination. The registry's adverse-event definition does not require a possible causal relationship, and treatment-emergent status is based on an event occurring after the first study treatment. Events occurring after treatment can have other explanations. With no comparison group, the study cannot estimate how these counts differ from what might have been observed under another condition.
The record also does not report the antibody outcome values, confidence intervals, statistical tests, or a distinct primary-endpoint result. The adverse-event denominator of 100 is lower than the enrollment total of 110, and the reason is not reported. These gaps limit assessment of precision, participant flow, and the relationship between the category-specific safety counts and the primary endpoint.
Nothing in these registry entries establishes a broader conclusion about safety in all plasma donors or about antibody response beyond the outcomes named. The study's single-group findings cannot be treated as comparative evidence. The registry record supports a description of the listed observations and study procedures, while conclusions requiring unreported results, uncertainty estimates, or a comparator remain unresolved.
13. Why This Trial Matters Statistically
This study illustrates an important distinction between describing safety experience and estimating a comparative effect. In a single-group study, event counts can document what was recorded among participants who received an intervention. Without a control group, however, those counts cannot show whether the observed experience differs from that expected without the intervention or under an alternative. That distinction is especially important when the endpoint includes events that are not required to be judged causally related to treatment.
The registry also makes clear why denominator definitions matter. Enrollment is 110, whereas the adverse-event figures use 100 at risk. Since the record does not explain the difference, readers cannot tell from the posted information which participants are represented in each safety summary or why others are not included. A clear account of participant flow and analysis populations is central to interpreting any count.
The study includes repeated antibody outcomes as well as a safety endpoint, but the registry record does not report their results or analysis methods. That illustrates the difference between listing an outcome and reporting evidence about it. For longitudinal outcomes, the statistical method must account appropriately for repeated observations and any incomplete follow-up; the particular methods used in this study are not reported.
Finally, planning assumptions should not be confused with the actual study design. The registry's sample-size illustrations describe a two-arm planning framework, while the listed trial is single group. These illustrations do not demonstrate observed power or supply a trial-specific justification. Keeping design, planning, and reported results distinct helps prevent unsupported conclusions from being drawn from registry information.
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 main design limitation is the absence of a comparison group. With a single group, observed adverse events cannot be contrasted with events in participants receiving another treatment or no study vaccination. The open-label design is also recorded, and the registry does not describe additional procedures intended to reduce the possibility that knowledge of treatment influenced event reporting or assessment.
The safety denominator requires caution: enrollment was 110, while 100 participants are listed at risk in the adverse-event information. The registry record does not explain the difference, report participant flow, or state how missing safety information was handled. The population definition for the primary endpoint requires receipt of at least one vaccination and safety data, but the number meeting that definition is not reported.
The posted safety categories are limited. The record gives 0 serious events, 71 other events, and 0 deaths for the stated denominators, but does not provide detailed terms for other events, their severity, timing, duration, or participant-level overlap. The empty serious-event term listing does not provide further characterization. The record also does not explicitly connect the other-event count to the primary endpoint result.
Although two secondary antibody outcomes are listed, their results and analysis methods are not reported. Confidence intervals, statistical tests, the analysis plan, multiplicity handling, and missing-data methods are also not reported in the registry record. Finally, the phase description differs: the registry phase listing identifies Phase 2 and Phase 3, while the brief summary calls the study Phase 1. The record does not reconcile these descriptions.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Tdap Vaccine Safety for Plasma Donors — NCT04142983.
- Registry record last updated 2022-12-06; status last verified 2022-11.
- Results first posted 2022-12-06.
- 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
NCT04142983 is a completed, prospective, open-label, single-group, multicenter study of Adacel vaccination in plasma donors. Enrollment was 110. The regimen described was 5 immunizations over 12 months, given every 3 months ±1 week, with a 6 month follow-up after the last vaccination. The primary endpoint was the number of participants with treatment-emergent adverse events over up to 18 months.
The adverse-event information reports 0 serious events and 0 deaths among 100 at risk, and 71 participants with other events among 100 at risk. The registry record does not explain why the adverse-event denominator differs from enrollment or identify the other-event count as the primary-endpoint result. Two secondary antibody outcomes are listed, but their results are not reported. No analyses are listed. The phase information differs between the registry phase listing and the brief summary.