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 A Study of the Safety and Immune Response of 2 Doses of a New Shigella Vaccine in Kenyan Adults (NCT02676895), a randomized phase 2 study. The primary outcome is Number of Subjects With Solicited Local and Systemic Adverse Reactions After Each Vaccination.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT02676895 |
| Phase | Phase 2 |
| Condition | Shigella Sonnei Infection |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | Quadruple |
| Enrollment | 74 |
| Arms in the primary outcome | n/a |
| Lead sponsor | GlaxoSmithKline |
| Results posted | Yes |
2. Clinical Question
Population
Healthy adults in a country where shigellosis is endemic were enrolled. The study title identifies the participants as Kenyan adults. The registry describes this as an early step toward testing the vaccine in children from developing countries where shigellosis is endemic; children were not the population studied in this trial.
Intervention
The intervention was the GVGH 1790GAHB vaccine against Shigella sonnei, given as two injections. The study compared a 25 μg formulation with a 100 μg formulation. The registry record does not report the interval between injections.
Comparator
The control group received one dose of Menveo and a second dose of Boostrix. The record does not describe these control vaccines as a placebo. It also does not report the allocation ratio among the groups.
Primary question
The primary outcome counted participants with solicited local and systemic adverse reactions after each vaccination. The study also assessed antibody responses to Shigella sonnei lipopolysaccharide. The registry record does not report a single summary comparison of the primary outcome or inferential analysis results.
3. Trial Design
This was a phase 2a, randomized, controlled, parallel-group, single-center study. The registry lists quadruple masking and an enrollment of 74. The study start date was 2016-08-08, primary completion was 2017-03-10, and the record lists the study as completed. The sponsor was GlaxoSmithKline.
Participants assigned to either vaccine group received two injections of 1790GAHB, containing 25 μg or 100 μg of Shigella sonnei, respectively. Participants in the control group received one dose of Menveo and a second dose of Boostrix. The interval between doses, the randomization ratio, and further details about allocation concealment are not reported in the registry record.
The study focused on safety, reactogenicity, and immunogenicity in adults from a country endemic for shigellosis. Its stated purpose included taking an early step toward testing the vaccine in the intended target population of children in developing countries where shigellosis is endemic. That future population is distinct from the adult population enrolled in this trial.
The registry record identifies 12 outcome measures, including solicited adverse reactions and several antibody-response outcomes. It lists zero analysis entries. It does not report a statistical analysis plan, the rationale for the enrollment target, or a detailed account of how participants were assigned to each group. Those omissions limit how fully the planned design can be reconstructed.
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.
Overall Study
| Stage | 1790GAHB 25 μg Group | 1790GAHB 100 μg Group | Control Group |
|---|---|---|---|
| STARTED | 22 | 26 | 24 |
| COMPLETED | 20 | 23 | 21 |
| NOT COMPLETED | 2 | 3 | 3 |
Reasons for not completing this period:
| Reason | 1790GAHB 25 μg Group | 1790GAHB 100 μg Group | Control Group |
|---|---|---|---|
| Administrative reason | 1 | 0 | 0 |
| Protocol Violation | 1 | 0 | 0 |
| Adverse Event | 0 | 3 | 1 |
| Lost to Follow-up | 0 | 0 | 1 |
| Withdrawal by Subject | 0 | 0 | 1 |
Analysis population for the primary outcome, as defined in the registry: This analysis was performed on the Solicited Safety Set, which included all enrolled subjects who received a study vaccination and for whom solicited adverse event data were available. Less subjects were available to receive the second dose, hence the number or participants analysed is lower for the second dose results.
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 | 1790GAHB 25 μg Group | 1790GAHB 100 μg Group | Control Group | Total |
|---|---|---|---|---|---|
| Participants analysed | 22 | 26 | 24 | 72 | |
| Age, Continuous | Years | 24.6 (SD 5.81) | 26.9 (SD 8.44) | 28.3 (SD 8.23) | 26.7 (SD 7.7) |
| Sex: Female, Male: Female | Participants | 2 | 3 | 3 | 8 |
| Sex: Female, Male: Male | Participants | 20 | 23 | 21 | 64 |
| Race/Ethnicity, Customized: Black/African American | Participants | 21 | 26 | 24 | 71 |
| Race/Ethnicity, Customized: White | Participants | 1 | 0 | 0 | 1 |
6. Primary Endpoint
The registry lists the primary outcome as Number of Subjects With Solicited Local and Systemic Adverse Reactions After Each Vaccination, measured over From 30 minutes up to 7 days following each vaccination.
| Element | Registry entry |
|---|---|
| Result type | Count Of Participants |
| Measure of spread | not applicable |
| Unit | Participants |
| Endpoint classification | Binary Endpoint |
The primary endpoint was the number of participants with solicited local and systemic adverse reactions, assessed from 30 minutes up to 7 days following each vaccination. Local reactions included injection-site erythema, induration, and pain. Systemic symptoms included headache, arthralgia, chills, fatigue, malaise, myalgia, and temperature measured axillary. The endpoint counted a symptom regardless of intensity under the definition of “any.”
The record also defined severe symptoms by their impact or extent: specified systemic symptoms and pain had to prevent normal activity; severe redness or swelling had to spread beyond 100 millimeters of the injection site; and severe temperature was defined as body temperature above 40.0 °C. “Any temperature” was defined as body temperature at least 38.0°C.
Counting affected participants is a direct way to describe how often specified reactions were reported in a safety population. Comparing those counts across groups can help characterize observed reactogenicity, but interpretation depends on the relevant denominators, assessment periods, and uncertainty around the estimates. The registry record does not report a single combined primary-outcome estimate or inferential comparison. The posted primary outcome includes multiple reaction categories and vaccination time points, so it should not be treated as one unqualified result.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record describes the study design and certain safety counts, but it does not report a single primary-outcome comparison or statistical analysis results. In particular, the primary outcome covers multiple local and systemic reactions after each vaccination. The record notes that it was not reduced to one comparison. Without outcome-specific counts and an analysis, the primary endpoint cannot be summarized as a single comparative estimate from this record.
For serious adverse events, the registry lists 2 affected participants among 22 at risk in the 1790GAHB 25 μg group, 3 among 26 in the 1790GAHB 100 μg group, and 1 among 24 in the control group. It lists zero deaths in each group. These figures describe the recorded serious-event experience; by themselves, they do not establish whether a particular event was caused by vaccination or whether groups differ beyond what could occur through chance.
The record names neutropenia as the top serious term and reports 11.5%. It does not state in this information which group or denominator that percentage refers to. It should therefore not be assigned to a particular arm or interpreted as a group-specific risk. The detailed event-level account and statistical comparison are not reported in the registry record.
The secondary outcomes include geometric mean concentrations and ratios for anti-LPS Shigella sonnei IgG, seroresponse counts, and counts above a post-vaccination concentration threshold of 121 U/mL. These outcomes address immune response, a different question from the primary safety endpoint. The record does not provide the corresponding outcome estimates or analyses in the information available for this interpretation.
Consequently, the registry record supports a description of the trial’s structure and selected safety counts, not a conclusion about the relative frequency of all solicited reactions or the size and precision of antibody responses. A careful reading keeps the reported counts, the missing comparative analyses, and the intended future population separate.
9. Statistical Methods Explained
What does a participant count represent?
The primary endpoint is a participant-level count: it concerns how many participants experienced a specified reaction, rather than the total number of separate symptom episodes. This distinction matters because one participant may report more than one symptom, or the same symptom at more than one assessment period. A count of participants with any reaction therefore answers a different question from a count of all reaction episodes.
For a participant count to be interpretable, it needs a clear event definition, a time window, and a denominator identifying who was assessed. The registry describes the solicited symptoms, the window from 30 minutes up to 7 days following each vaccination, and a Solicited Safety Set made up of enrolled participants who received a study vaccination and had solicited adverse-event data available. It also notes that fewer participants were available to receive the second dose, so fewer participants were analyzed for that period. The exact per-outcome denominators are not reported in the registry record.
Why do the reaction categories matter?
The endpoint includes multiple local and systemic symptoms, intensity definitions, and vaccination occasions. Each category can have a different frequency and clinical meaning. Combining categories can make a compact summary, but a combined measure must be defined in advance and interpreted as the specific combination it represents. A broad “any reaction” measure, for example, does not describe which symptom occurred or its severity. The registry record does not report one primary comparison collapsed across all categories and time points.
When many outcomes or categories are examined, the chance of seeing an apparently unusual result somewhere can increase. Statistical approaches for handling multiple comparisons may include prespecifying a primary contrast, adjusting significance thresholds, or treating secondary findings as exploratory. Which approach was planned or used is not reported in the registry record. The registry lists 12 outcome measures and zero analysis entries, so the record does not establish a multiplicity strategy or provide inferential results to assess.
How should uncertainty be understood?
A confidence interval is a general statistical tool for expressing the range of estimates reasonably compatible with the observed data under the model and procedure used. A narrow interval indicates greater precision than a wide interval, while an interval that spans a range of plausible effects may leave substantial uncertainty. A confidence interval does not establish causation, correct bias, or resolve differences in how outcomes were collected. No confidence intervals for the primary outcome are reported in the registry record.
For binary outcomes such as whether a participant experienced a reaction, estimates can be sensitive to the number of participants assessed and the number of events. In small groups, a modest change in the observed count can materially affect the estimated proportion. The study’s listed enrollment is 74, but the primary outcome’s group- and time-specific denominators and reaction counts are not reported in the information. It would therefore be inappropriate to calculate or infer a comparative estimate from the enrollment figure alone.
Why are the antibody outcomes expressed differently?
Antibody concentration outcomes are not the same kind of measure as reaction counts. A geometric mean concentration summarizes values on a multiplicative scale and is commonly used when measurements are positive and may be skewed. A geometric mean ratio compares concentrations across two conditions or time points on that scale. These are general interpretations of the measures named in the registry; the record does not state the transformation, model, or analysis procedure used for these outcomes.
The listed immune-response outcomes also include seroresponse and the number of participants with a post-vaccination concentration at least 121 U/mL. A threshold count answers how many participants crossed a specified cutoff; it does not reveal the full distribution of concentrations. The registry record does not provide the outcome values, definitions beyond those listed, or uncertainty estimates needed to interpret these immune-response measures quantitatively.
What does the planning illustration mean?
The stated sample-size assumptions describe a planning illustration based on a fraction of the observed effect, with a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. The illustration is not the trial’s own design justification, and the record does not report the study’s original sample-size rationale. Sample-size illustrations are hypothetical planning quantities, not observed power. They should not be read as evidence that the study had a particular probability of detecting an effect after the data were collected. Specific planning estimates are not reported in the registry record.
10. Multiplicity, Missing Data and Analysis Populations
The trial listed 12 outcome measures, including multiple safety categories and immune-response measures. The primary safety endpoint itself spans several local and systemic reactions and vaccination time points. Examining several outcomes can create multiplicity: even when each test uses a conventional decision threshold, the chance of at least one chance finding across many tests may be higher than for a single prespecified test. The registry record does not report whether multiplicity was controlled, which outcomes were treated as confirmatory, or what comparisons were prespecified.
The registry lists zero analysis entries and does not report p-values, confidence intervals, adjusted estimates, or a statistical analysis plan. Therefore, it is not possible to determine from this record how uncertainty was quantified or how any multiple comparisons were handled.
The stated Solicited Safety Set included enrolled participants who received a study vaccination and had solicited adverse-event data available. The record notes that fewer participants were available to receive the second dose, resulting in fewer participants analyzed for that period. The reason for this reduction, exact outcome-specific denominators, and the handling of missing observations are not reported in the registry record. The definition does not establish whether every participant was included in every analysis or how participants with incomplete follow-up were treated.
These gaps matter because missing observations can affect both the denominator and the interpretation of a participant count. If availability differs by dose or group, comparisons may reflect differences in who was observed as well as differences in recorded events. The record does not provide enough detail to assess that possibility. No assumptions about missing outcomes or analysis populations beyond the stated safety-set description can be established from 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 |
|---|---|---|---|
| 1790GAHB 25 μg Group | 2 | 22 | 9.1% |
| 1790GAHB 100 μg Group | 3 | 26 | 11.5% |
| Control Group | 1 | 24 | 4.2% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| 1790GAHB 25 μg Group | 0 of 22 |
| 1790GAHB 100 μg Group | 0 of 26 |
| Control Group | 0 of 24 |
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 |
|---|---|
| 1790GAHB 25 μg Group | 22 of 22 |
| 1790GAHB 100 μg Group | 26 of 26 |
| Control Group | 24 of 24 |
Most frequent serious adverse event terms
| Event term | Organ system | 1790GAHB 25 μg Group | 1790GAHB 100 μg Group | Control Group |
|---|---|---|---|---|
| Neutropenia | Blood and lymphatic system disorders | 2 of 22 | 3 of 26 | 1 of 24 |
Most frequent non-serious adverse event terms
| Event term | Organ system | 1790GAHB 25 μg Group | 1790GAHB 100 μg Group | Control Group |
|---|---|---|---|---|
| Injection site pain | General disorders | 21 of 22 | 25 of 26 | 19 of 24 |
| Injection site induration | General disorders | 17 of 22 | 22 of 26 | 18 of 24 |
| Injection site erythema | General disorders | 15 of 22 | 18 of 26 | 14 of 24 |
| Headache | Nervous system disorders | 11 of 22 | 14 of 26 | 11 of 24 |
| Fatigue | General disorders | 3 of 22 | 9 of 26 | 9 of 24 |
| Limb discomfort | Musculoskeletal and connective tissue disorders | 5 of 22 | 7 of 26 | 6 of 24 |
| Malaise | General disorders | 3 of 22 | 3 of 26 | 10 of 24 |
| Chills | General disorders | 5 of 22 | 5 of 26 | 5 of 24 |
| Arthralgia | Musculoskeletal and connective tissue disorders | 1 of 22 | 5 of 26 | 5 of 24 |
| Myalgia | Musculoskeletal and connective tissue disorders | 1 of 22 | 3 of 26 | 7 of 24 |
Serious events with the highest arm-level rate: neutropenia (11.5%).
The registry lists participants with serious adverse events and the corresponding numbers at risk. In the 1790GAHB 25 μg group, 2 participants were affected among 22 at risk; in the 1790GAHB 100 μg group, 3 were affected among 26 at risk; and in the control group, 1 was affected among 24 at risk. The recorded number of deaths was zero in each group.
These are descriptive counts. They do not show whether an event was caused by a study vaccine, and they are not a statistical test of differences between groups. Serious adverse events are also distinct from the solicited local and systemic reactions that make up the primary endpoint. The two kinds of information should not be combined as if they measured the same outcome.
The registry identifies neutropenia as the top serious term and reports 11.5%. The group or denominator associated with that percentage is not stated in the record information, so it cannot be interpreted as an arm-specific figure. Detailed event descriptions, timing, and a comparative analysis are not reported in the registry record.
12. What the Result Does, and Does Not, Mean
This trial’s record documents a randomized, controlled study of two 1790GAHB dose levels in adults and describes a control group receiving Menveo and Boostrix. It identifies solicited reactions as the primary outcome and antibody measures as secondary outcomes. These features clarify the questions the study was designed to address, but they are not themselves evidence of a particular effect.
The serious adverse-event counts provide a limited descriptive account for the groups, along with zero recorded deaths in each group. They do not establish that an event was caused by a vaccine, rule out uncommon harms, or establish equivalence between groups. The registry record does not report the complete primary safety results or an inferential comparison. It also does not report the listed immune-response estimates in the information used for this interpretation.
In general, a randomized design can support a comparative interpretation when outcomes, denominators, analysis methods, and uncertainty estimates are reported and the analysis is appropriate. Randomization alone does not supply those missing results. Nor does a small set of recorded serious-event counts answer the separate question of how often solicited reactions occurred after each dose.
The findings described in the registry are specific to adults in a country endemic for shigellosis. The study’s stated longer-term aim concerned testing in children from developing countries where shigellosis is endemic, but this adult trial does not directly report outcomes in children. The record therefore describes an early adult study, not evidence about outcomes in that future population.
Overall, the record allows readers to understand the trial’s question and selected serious-event counts, while leaving the comparative primary endpoint, immune-response estimates, and their precision unreported. No conclusion about the relative benefits or harms of the vaccine doses can be drawn from the information recorded alone.
13. Why This Trial Matters Statistically
The trial is statistically informative as an example of how a clear study question can involve several different outcome families. Solicited reactions are participant-level safety outcomes, serious adverse events are a separate safety category, and antibody concentrations and response thresholds address immunogenicity. Each needs its own definition, denominator, and interpretation. Treating them as interchangeable would obscure what was actually measured.
The registry also illustrates why reporting the analysis matters as much as reporting the design. Random allocation and masking describe how the study was structured, but they do not reveal the estimates, uncertainty, or comparison used to answer the primary question. With several symptoms and assessment periods, the choice of summary and approach to multiplicity can affect how results should be read. Those details are not reported in the registry record.
Another statistical issue is changing availability across vaccination periods. The record notes that fewer participants were available for the second dose and that fewer were analyzed for that period. Reporting the exact denominators and explaining missing observations would help readers distinguish the observed reaction pattern from changes in the population contributing data.
Finally, the study’s adult population and stated longer-term aim in children are not the same. Statistical evidence is tied to the population observed and the outcomes reported. Making that boundary explicit helps prevent an early adult study from being interpreted as if it directly answered questions about children or provided a complete comparative safety analysis.
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 registry record contains incomplete primary-outcome information for a full statistical interpretation. The primary endpoint covers several reactions and vaccination time points, but the record does not report a single comparison, outcome-specific counts, or uncertainty estimates. The listed analysis count is zero, and a detailed statistical analysis plan is not reported.
Participant availability differed by vaccination period: the record says fewer subjects were available to receive the second dose and that fewer participants were analyzed for that period. It does not give the reason, the precise denominators for each outcome, or the methods used to handle missing data. These omissions prevent assessment of whether the analyzed groups remained comparable for each period.
The registry lists serious-event counts and deaths by group, but it does not provide an inferential comparison or establish causality. The reported 11.5% for neutropenia is not linked to a stated group or denominator in the record information. The full context of that term is therefore unclear.
The study was conducted in adults, while the stated future target population is children in developing countries where shigellosis is endemic. Results in adults cannot automatically be applied to that distinct population. The record also does not report the interval between vaccine doses, the allocation ratio, the original sample-size rationale, or whether and how interim analyses were planned.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: A Study of the Safety and Immune Response of 2 Doses of a New Shigella Vaccine in Kenyan Adults — NCT02676895.
- Registry record last updated 2019-02-18; status last verified 2018-10.
- Results first posted 2019-02-18.
- 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 2a randomized, controlled, parallel-group, single-center study evaluated two doses of the GVGH 1790GAHB Shigella sonnei vaccine in adults from a country endemic for shigellosis. The vaccine groups received two injections containing 25 μg or 100 μg; the control group received Menveo followed by Boostrix. The registry lists quadruple masking and enrollment of 74.
The primary outcome counted solicited local and systemic adverse reactions after each vaccination. Secondary outcomes included anti-LPS Shigella sonnei IgG concentrations, ratios, seroresponse, and a post-vaccination concentration threshold. The registry lists 12 outcome measures and zero analysis entries. It reports serious adverse-event counts of 2 among 22, 3 among 26, and 1 among 24 across the three groups, with zero deaths in each. A single primary-outcome comparison, analysis results, and uncertainty estimates are not reported in the registry record.