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 and Efficacy Study of WRSS1, a Shigella Sonnei Vaccine Candidate (NCT01080716), a randomized phase 1, phase 2 study. The primary outcome is Number of Participants With Adverse Events.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT01080716 |
| Phase | Phase 1, Phase 2 |
| Condition | Dysentery, Shigella, Diarrhea |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | Triple |
| Enrollment | 30 |
| Arms in the primary outcome | n/a |
| Lead sponsor | U.S. Army Medical Research and Development Command |
| Results posted | Yes |
2. Clinical Question
Population
The study enrolled healthy Thai adults. The registry describes it as an inpatient trial and lists dysentery, Shigella, and diarrhea among its conditions. The recorded enrollment is 30. The registry record does not give further eligibility criteria or a detailed description of the analysis population for the primary outcome.
Intervention
In Part 1, one arm received WRSS1, a live attenuated S. sonnei vaccine candidate derived from the Mosely strain, and the other received placebo. In Part 2, the registry describes administration of S. sonnei 53G to volunteers from the WRSS1 arm and to naïve controls. The record’s intervention descriptions do not provide a complete account of how participants moved between parts or how alternates were handled in the outcome analysis.
Comparator
The Part 1 comparator was placebo. The Part 2 descriptions distinguish volunteers previously assigned to WRSS1 from naïve controls; both groups are described as receiving S. sonnei 53G. These are different comparisons from the vaccine-versus-placebo comparison in Part 1, so the recorded groups should not be treated as interchangeable arms of a single simple comparison.
Primary question
The primary outcome is the number of participants with adverse events, with a timeframe of up to 12 months. The registry says the overview highlights all adverse events, withdrawals, and deaths related to adverse events. The posted results give counts of participants affected by serious and other adverse events in the listed groups. They do not give a single statistical comparison that answers whether the groups differ, nor do they establish vaccine efficacy.
3. Trial Design
The registry describes a randomized, triple-masked, parallel study in Phase 1 and Phase 2. Its title identifies WRSS1 as a live attenuated Shigella sonnei vaccine candidate, and its brief summary describes an inpatient trial intended to assess safety, immunogenicity, and efficacy in healthy Thai adult volunteers. These stated aims are not equivalent to reported results: the recorded primary outcome concerns adverse events, and the posted information does not provide a complete efficacy or immunogenicity analysis.
Part 1 had a WRSS1 vaccine arm and a placebo arm. Part 2 had two groups described as receiving S. sonnei 53G: volunteers from the WRSS1 arm and naïve controls. The record says that 10 volunteers from the Part 1 WRSS1 arm plus 4 alternates were given 53G, and that 10 naïve controls plus 4 alternates were given 53G. Those descriptions identify the groups’ stated histories and challenge intervention, but do not fully explain the timing, participant flow, or which people contributed to each posted outcome count.
The registry records enrollment of 30 and a completed status. The recorded study start is 2010-05 and primary completion is 2010-09. The sponsor is the U.S. Army Medical Research and Development Command. One secondary outcome is the count of subjects with normal and abnormal clinical laboratory values during Parts 1 and 2. The record lists 3 outcome measures, but does not provide a statistical analysis for the primary outcome. A sample-size justification, detailed protocol, and fuller account of randomization and masking procedures 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: Part 1 - total of 20 volunteers (14 vaccinees and 6 controls) Part 2 - was started approximately 60 days after WRSS1 vaccination. 10 vaccinees from part 1 and 10 naïve controls
Part 1
| Stage | Arm 1: WRSS1 Vaccine | Arm 1: Placebo Vaccine | Arm 2: S. Sonnei 53G | Arm 2: S. Sonnei 53G (Naive Subjects) |
|---|---|---|---|---|
| STARTED | 14 | 6 | 0 | 0 |
| COMPLETED | 13 | 6 | 0 | 0 |
| NOT COMPLETED | 1 | 0 | 0 | 0 |
Reasons for not completing this period:
| Reason | Arm 1: WRSS1 Vaccine | Arm 1: Placebo Vaccine | Arm 2: S. Sonnei 53G | Arm 2: S. Sonnei 53G (Naive Subjects) |
|---|---|---|---|---|
| Physician Decision | 1 | 0 | 0 | 0 |
Part 2
| Stage | Arm 1: WRSS1 Vaccine | Arm 1: Placebo Vaccine | Arm 2: S. Sonnei 53G | Arm 2: S. Sonnei 53G (Naive Subjects) |
|---|---|---|---|---|
| STARTED | 0 | 0 | 10 | 10 |
| COMPLETED | 0 | 0 | 10 | 10 |
| NOT COMPLETED | 0 | 0 | 0 | 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 | Part 1/Arm 1 of Study: WRSS1 Vaccine | Part 1/Arm 2 of Study: Placebo Vaccine | Part 2/Arm 1 of Study: S. Sonnei 53G | Part 2/Arm 2 of Study: S Sonnei 53G (Controls) | Total |
|---|---|---|---|---|---|---|
| Participants analysed | 13 | 6 | 10 | 10 | 39 | |
| Age, Categorical: <=18 years | Participants | 0 | 0 | 0 | 0 | 0 |
| Age, Categorical: Between 18 and 65 years | Participants | 13 | 6 | 10 | 10 | 39 |
| Age, Categorical: >=65 years | Participants | 0 | 0 | 0 | 0 | 0 |
| Sex: Female, Male: Female | Participants | 8 | 3 | 5 | 2 | 18 |
| Sex: Female, Male: Male | Participants | 5 | 3 | 5 | 8 | 21 |
| Region of Enrollment: Thailand | participants | 13 | 6 | 10 | 10 | 39 |
6. Primary Endpoint
The registry lists the primary outcome as Number of Participants With Adverse Events, measured over Up to 12 months.
| Element | Registry entry |
|---|---|
| Result type | Count Of Participants |
| Measure of spread | not applicable |
| Unit | Participants |
| Endpoint classification | Binary Endpoint |
The primary endpoint is the number of participants with adverse events during a timeframe of up to 12 months. It is a participant count: it concerns whether participants experienced an event, rather than the total number of event episodes. The endpoint description says the overview covers all adverse events, withdrawals, and deaths related to adverse events. However, the posted results do not give separate withdrawal counts or death counts, and the registry record does not report a detailed definition of which events were included in each category.
Counting participants with events is useful in a safety assessment because it describes how many people in each reported group were affected. It can be read alongside the distinction between serious adverse events and other adverse events in the posted results. A count alone does not convey event type, severity beyond the serious classification, duration, timing, or whether an event was judged related to vaccination or challenge. Those details are not reported in the registry record.
The outcome is not a direct measure of immunogenicity or protection against disease. Although the study summary names safety, immunogenicity, and efficacy as aims, this endpoint reports adverse-event counts. The registry record does not provide a primary efficacy estimate or a statistical comparison for this outcome. As a result, the counts describe the recorded safety observations but do not by themselves resolve comparisons between the groups.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The posted results separate serious adverse events from other adverse events. For Part 1/Arm 1, the WRSS1 vaccine group, 0 of 13 participants at risk had a serious adverse event, and 9 of 13 had an other adverse event. For Part 1/Arm 2, the placebo group, 0 of 6 had a serious adverse event, and 5 of 6 had an other adverse event. In Part 2/Arm 1, the group described as receiving S. sonnei 53G after WRSS1, 0 of 10 had a serious adverse event, and 8 of 10 had an other adverse event. In Part 2/Arm 2, the S. sonnei 53G control group, 0 of 10 had a serious adverse event, and 10 of 10 had an other adverse event.
These are descriptive counts. The registry record does not report a statistical test, confidence interval, adjusted estimate, or inferential comparison for them. The counts therefore do not establish whether the observed differences between groups reflect a real difference or chance variation. They also cannot be used to claim that WRSS1 caused, prevented, or had no effect on adverse events. In particular, Part 2 includes groups with different prior histories, and both are described as receiving 53G; it is not the same comparison as vaccine versus placebo in Part 1.
The reported serious adverse-event count is zero in each listed group, but the groups are small as recorded in the outcome data. A zero count means that no serious adverse events were reported among those at risk in these entries; it does not demonstrate that serious events are impossible or rule out uncommon risks. The registry record gives no serious-event terms. Death counts are recorded as unavailable, so they should not be interpreted as zero. Likewise, the endpoint description mentions withdrawals related to adverse events, but separate withdrawal counts are not reported in the registry record.
The other adverse-event counts indicate that events outside the serious category were recorded in each group. They do not indicate how many events each participant experienced, what the events were, when they occurred, or whether they were judged related to the study interventions. No conclusion about efficacy or immunogenicity follows from these safety counts. The registry’s stated study aims are broader than the outcome information available in these results.
9. Statistical Methods Explained
Several statistical ideas help clarify what the registry results can and cannot show. The observed values are participant counts, not effect estimates from a statistical model. They summarize the number of people recorded as affected in each group. A count can be informative as a direct description, but interpreting it as evidence of a comparative effect requires additional information about the outcome definitions, the participants included, and the analysis used.
What does a participant count represent?
A participant-level adverse-event count records whether a person had an event in the relevant category during the stated observation period. It is distinct from an event count: a participant with repeated events may still contribute once to a participant count. The registry outcome is titled as the number of participants with adverse events, and the posted results distinguish serious adverse events from other adverse events. The record does not describe how repeated events, event timing, or multiple event types were handled, so those aspects cannot be reconstructed from the counts.
Counts are often accompanied by denominators, which identify the number of participants at risk for the outcome. The posted group entries include those at-risk counts. Reading the count together with its denominator gives context for the amount of observed information, but it does not by itself supply a confidence interval or a formal test. No such inferential result is reported for the primary endpoint in the registry record.
Why do small groups limit precision?
In general, estimates based on small groups tend to be less precise than estimates based on larger groups, because each participant’s outcome has more influence on the observed group result. A zero count is compatible with the absence of recorded events in that group, but it is not proof that the underlying risk is zero. The registry’s serious-event counts are zero across the listed groups, while the recorded at-risk counts remain limited. Without a confidence interval or other uncertainty estimate, the degree of precision cannot be quantified from the posted results.
General statistical interpretation also distinguishes absence of evidence from evidence of no difference. A formal comparison would need an estimand, such as a specified contrast between groups, and an analysis suited to the outcome and study design. The registry record reports no analysis for the primary outcome. It therefore does not provide the information needed to assess statistical evidence for a difference between the WRSS1 and placebo groups, or between the Part 2 groups.
What would a confidence interval add?
In general, a confidence interval expresses the uncertainty around an estimated effect under a stated statistical method. It can show which effect values are reasonably compatible with the data and method, while helping readers distinguish a precise estimate from a highly uncertain one. A confidence interval is not reported for these adverse-event counts. No interval should be inferred from the raw counts alone in this interpretation.
Similarly, a p-value would summarize how compatible the data are with a specified null hypothesis under a particular model. It does not state the probability that the null hypothesis is true or measure clinical importance. The registry record reports no p-value or test for the primary outcome. Any comparison of the displayed counts by eye is descriptive, not a substitute for the trial’s own analysis.
What do the sample-size assumptions mean?
The record describes a planning illustration based on the observed effect, with a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. It says the effect to detect is a stated fraction of the observed effect. These are assumptions for an illustrative planning calculation, not evidence about the study’s original design or its actual power. The registry record does not report the trial’s own sample-size justification, and the planning illustration should not be read as observed power. A calculation based on an observed effect also depends on that effect and does not repair missing inferential analysis.
The stated method distinguishes participants per arm for non-time-to-event outcomes from total events for time-to-event outcomes. The primary endpoint is a participant count, not a time-to-event measure. No numerical planning result is needed to interpret the posted safety counts, and such planning quantities do not constitute observed trial outcomes.
Why do design details matter?
Randomization can support a fair comparison by balancing prognostic factors on average, while masking can reduce some forms of influence on care, reporting, and assessment. These are general purposes of those design features. The registry identifies the trial as randomized and triple-masked, but does not report the detailed procedures, concealment method, or which roles were masked. The parallel-model designation describes the registered design classification; it does not explain all transitions between the Part 1 and Part 2 groups.
Part 2 is described as giving 53G to volunteers from the WRSS1 arm and to naïve controls. That means the groups have different prior histories as described in the record. A comparison of their adverse-event counts would need to account for the question being asked and the sequence of study procedures. The registry record does not provide a statistical analysis plan specifying such a comparison. Consequently, the most defensible interpretation is to retain the group-specific descriptive counts and avoid attributing differences to a particular intervention.
10. Multiplicity, Missing Data and Analysis Populations
The registry record lists 3 outcome measures and identifies a secondary outcome concerning normal and abnormal clinical laboratory values during Parts 1 and 2. It does not report a complete hierarchy of primary and secondary hypotheses, a multiplicity adjustment, or a statistical analysis plan. When a study examines multiple outcomes or comparisons, general statistical practice recognizes that the chance of a false-positive finding can increase if each is tested without accounting for the full set. Whether and how that issue was handled in this trial is not reported in the registry record.
The posted results do not give an analysis population for the adverse-event endpoint, such as a detailed rule for including participants who did not complete all study procedures. The registry record also does not report missing outcome data, participant-level follow-up completeness, or a method for handling missing values. The stated timeframe is up to 12 months, but the record does not describe individual observation times or whether all participants were observed for the same duration.
These omissions matter because an adverse-event count depends on who was followed and for how long. If follow-up differs, simple counts may not represent comparable observation opportunities. This is a general consideration, not a claim that follow-up differed in this study. Without the missing details, the posted counts should be read as registry-reported summaries rather than as a fully specified comparative analysis.
No primary-outcome analysis is listed in the record. Accordingly, no adjustment, missing-data method, or population definition should be presumed. The registry record does not report whether interim analyses were planned or conducted.
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 |
|---|---|---|---|
| Part 1/Arm 1 of Study: WRSS1 Vaccine | 0 | 13 | 0.0% |
| Part 1/Arm 2: Placebo | 0 | 6 | 0.0% |
| Part 2/Arm 1 of Study: S. Sonnei 53G | 0 | 10 | 0.0% |
| Part 2/Arm 2 of Study: S Sonnei 53G (Controls) | 0 | 10 | 0.0% |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 0% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Part 1/Arm 1 of Study: WRSS1 Vaccine | 9 of 13 |
| Part 1/Arm 2: Placebo | 5 of 6 |
| Part 2/Arm 1 of Study: S. Sonnei 53G | 8 of 10 |
| Part 2/Arm 2 of Study: S Sonnei 53G (Controls) | 10 of 10 |
Most frequent non-serious adverse event terms
| Event term | Organ system | Part 1/Arm 1 of Study: WRSS1 Vaccine | Part 1/Arm 2: Placebo | Part 2/Arm 1 of Study: S. Sonnei 53G | Part 2/Arm 2 of Study: S Sonnei 53G (Controls) |
|---|---|---|---|---|---|
| Headache | Nervous system disorders | 8 of 13 | 2 of 6 | 4 of 10 | 2 of 10 |
| Diarrheic stool | Gastrointestinal disorders | 2 of 13 | 4 of 6 | 4 of 10 | 2 of 10 |
| Water stool | Gastrointestinal disorders | 2 of 13 | 1 of 6 | 1 of 10 | 6 of 10 |
| Feverish | General disorders | 3 of 13 | 0 of 6 | 2 of 10 | 3 of 10 |
| Dizziness | Nervous system disorders | 0 of 13 | 0 of 6 | 4 of 10 | 4 of 10 |
| Myalgia | Musculoskeletal and connective tissue disorders | 1 of 13 | 0 of 6 | 1 of 10 | 5 of 10 |
| Common cold | Respiratory, thoracic and mediastinal disorders | 0 of 13 | 1 of 6 | 2 of 10 | 3 of 10 |
| Malaise | General disorders | 0 of 13 | 1 of 6 | 3 of 10 | 2 of 10 |
| Abdominal pain | Gastrointestinal disorders | 1 of 13 | 2 of 6 | 0 of 10 | 1 of 10 |
| Insomnia (sleep difficulty) | Psychiatric disorders | 1 of 13 | 0 of 6 | 2 of 10 | 1 of 10 |
The serious adverse-event entries report 0 affected participants in each listed group: WRSS1 vaccine, placebo, S. sonnei 53G after WRSS1, and S. sonnei 53G controls. The corresponding at-risk counts are 13, 6, 10, and 10. These values describe the posted serious-event results; they do not establish that the risk of a serious event is zero.
The registry lists no serious-event terms. Death fields are unavailable, so deaths are not reported in the registry record rather than confirmed absent. Although the primary-outcome description mentions withdrawals related to adverse events, separate withdrawal figures are not reported. The other adverse-event counts are reported separately and should not be mistaken for serious adverse events.
In general, safety counts need context about event definitions, timing, severity, relatedness, and completeness of follow-up. Those details are not reported in the registry record. The counts are descriptive and do not provide a formal comparison or establish the cause of any event.
12. What the Result Does, and Does Not, Mean
The posted results establish that the registry records adverse-event counts for four group entries. They show zero reported serious adverse events in each entry and report other adverse events in each. The registry identifies Part 1 as a WRSS1-versus-placebo comparison and Part 2 as groups receiving S. sonnei 53G with different described prior histories. This information supports a factual description of the recorded safety observations.
The results do not establish that WRSS1 is safe or unsafe in a broader population, and they do not establish whether the vaccine prevents disease. The study summary names immunogenicity and efficacy as aims, but the results described in the registry record do not include an efficacy estimate, immunogenicity result, or formal statistical comparison of adverse-event counts. No statistical analysis is reported for the primary outcome. The raw counts therefore cannot answer whether group differences are statistically distinguishable from chance.
Nor do zero serious-event counts prove that serious events cannot occur. They indicate that none were reported among the participants at risk in the listed entries. Death counts are not available, and withdrawal counts are not separately reported. The record does not provide event descriptions, relatedness judgments, follow-up completeness, or the analysis population. These gaps limit both clinical interpretation and statistical precision.
Interpretation should also preserve the distinction between study parts. The Part 1 vaccine and placebo groups are not identical in size in the posted outcome entries, and Part 2 compares groups with different prior histories who are both described as receiving 53G. Without a stated analysis that defines the intended contrast, these groups should not be collapsed into a single effect estimate. The registry information is best read as a limited descriptive safety record, not as a complete account of the trial’s planned or achieved inferential conclusions.
13. Why This Trial Matters Statistically
This trial illustrates why registry results require attention to the level of detail behind a reported count. A participant count is easy to understand, but its meaning depends on the event definition, observation period, denominator, and analysis population. Here, the primary endpoint is described as the number of participants with adverse events over up to 12 months, while the posted entries distinguish serious from other adverse events. The registry does not supply all the details needed to interpret those categories fully.
The study also has more than one kind of comparison. Part 1 contrasts WRSS1 with placebo; Part 2 describes 53G administration to volunteers with different prior histories. Treating all entries as if they formed a single parallel comparison would obscure those distinctions. This is a useful statistical lesson: a design label alone does not define the estimand, and a group label does not substitute for a prespecified contrast.
Finally, the record separates descriptive results from inferential claims. It lists adverse-event counts but no analysis for the primary outcome, confidence interval, or p-value. Small-group safety observations can identify what was recorded, but cannot on their own quantify uncertainty or rule out uncommon events. The record’s planning illustration is not a substitute for the trial’s own sample-size justification or an analysis of observed outcomes. These distinctions matter when registry records are used to understand what a study can support and what remains uncertain.
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 adverse-event data are reported as counts by group, but the registry record does not give event terms, onset times, duration, severity beyond the serious classification, or judgments about relation to study interventions. It does not report separate withdrawal counts or deaths; the death fields are unavailable. These limits prevent a fuller characterization of the safety profile from the recorded summaries.
The record does not describe whether all participants had the same duration of observation within the timeframe of up to 12 months, or how missing follow-up was handled. It also does not specify the analysis population or explain how the Part 2 alternates contributed to the outcome entries. The intervention descriptions identify prior WRSS1 recipients and naïve controls, but do not fully document participant flow between parts.
Although the study is registered as randomized, triple-masked, and parallel, detailed randomization and masking procedures are not reported in the registry record. A statistical analysis plan, primary-outcome comparison, confidence interval, and hypothesis test are also not reported. The efficacy and immunogenicity aims in the summary are not accompanied by results in the registry record used for this analysis. Therefore, interpretation is limited to the recorded adverse-event counts and the study descriptions, rather than conclusions about comparative effects or efficacy.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Safety and Efficacy Study of WRSS1, a Shigella Sonnei Vaccine Candidate — NCT01080716.
- Registry record last updated 2018-11-13; status last verified 2018-10.
- Results first posted 2018-11-13.
- 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.
Continue through the Clinical Biostats statistical pathway
Use this trial's endpoint as a starting point for deeper study of effect measures, confidence intervals, and sample-size planning.
18. Record Summary
The registry record identifies a completed randomized, triple-masked, parallel Phase 1 and Phase 2 study of WRSS1 in healthy Thai adults. Part 1 compared WRSS1 vaccine with placebo; Part 2 described S. sonnei 53G administration to volunteers previously assigned to WRSS1 and to naïve controls. The primary endpoint was the number of participants with adverse events up to 12 months.
Posted results report zero serious adverse events in each listed group and nonzero counts for other adverse events. The record does not report a statistical analysis of the primary outcome, separate death or withdrawal counts, or detailed event descriptions. It also does not provide a formal efficacy or immunogenicity result in the information used for this analysis. The counts should therefore be interpreted as descriptive registry results, with substantial limits on comparative and causal conclusions.