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 Phase 2 Study to Evaluate the Safety and Immunogenicity of Two Oral Poliovirus Vaccine Candidates (NCT04544787), a randomized phase 2 study. The primary outcome is Number of Participants With Serious Adverse Events (SAEs) and Severe Adverse Events.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT04544787 |
| Phase | Phase 2 |
| Condition | Poliomyelitis |
| Allocation | Randomized |
| Design model | Sequential |
| Masking | Quadruple |
| Enrollment | 250 |
| Arms in the primary outcome | n/a |
| Lead sponsor | Pierre Van Damme |
| Results posted | Yes |
2. Clinical Question
Population
Healthy adults previously vaccinated with oral polio vaccine (OPV) or inactivated polio vaccine (IPV). The primary endpoint describes the total vaccinated population: randomized participants who received at least one dose of study vaccine.
Intervention
Novel live attenuated serotype 2 oral poliovirus vaccine candidates 1 and 2. OPV-vaccinated participants received one or two doses of either candidate; IPV-vaccinated participants received two doses of either candidate.
Comparator
IPV-vaccinated participants assigned to two doses of placebo form a placebo group. The official title also refers to historical controls given Sabin OPV2 or placebo; details of those historical controls are not reported in the registry record.
Primary question
How many participants experienced serious adverse events (SAEs) or severe adverse events during follow-up up to 42 days after each vaccination? The posted safety counts describe serious events and other affected participants, but the registry record does not present a single comparative estimate for the combined primary endpoint.
The study concerns safety and immunogenicity in adults with prior polio vaccination, not a direct comparison in an unvaccinated population. Its groups differ by prior vaccine type, candidate, dose schedule, and, for the IPV-vaccinated participants, placebo assignment. Those features define the clinical comparisons that could be considered, but they also mean that a contrast between any two groups must be interpreted in light of their different vaccination histories and schedules.
The record describes candidate vaccines as administered orally. For OPV-vaccinated participants, candidate 1 and candidate 2 were each evaluated as a one-dose and a two-dose schedule. For IPV-vaccinated participants, each candidate was evaluated as a two-dose schedule, alongside two doses of placebo. The primary question is therefore broad: it addresses serious and severe adverse events across multiple groups and follow-up after vaccination, rather than one plainly specified pairwise comparison.
3. Trial Design
This was a randomized, Phase 2, multicenter study with a sequential model. The registry lists quadruple masking, while the official title describes the study as partial blind. The record does not explain how those two descriptions relate to one another. Enrollment is recorded as 250. The study is marked completed, with a start date of 2018-10-22 and a primary completion date of 2019-01-31.
The groups were organized by participants’ previous polio vaccination. OPV-vaccinated participants were assigned one dose or two doses, 28 days apart, of candidate 1 or candidate 2. IPV-vaccinated participants were assigned two doses, 28 days apart, of candidate 1, candidate 2, or placebo. Vaccinations were oral. The record describes each vaccine dose as six drops, 0.3 mL total, and approximately 10⁶ CCID50; placebo was also given as six drops, 0.3 mL total.
The primary outcome was the number of participants with SAEs and severe adverse events, assessed up to 42 days after each vaccination. The registry defines SAEs by seriousness criteria, including death, life threat, inpatient hospitalization or its prolongation, persistent or significant disability or incapacity, congenital anomaly or birth defect, or medical importance. Severe adverse events were defined separately as events preventing normal everyday activities that were not classified as SAEs.
The registry lists 13 outcome measures and 12 analyses. Secondary outcomes include solicited and unsolicited adverse events, clinically relevant laboratory abnormalities, neutralizing antibody titers, and seroprotection measures. The brief summary describes evaluation of safety and immunogenicity in healthy volunteers previously vaccinated with Sabin monovalent OPV or IPV only. No further account of the sequential allocation process, site structure, randomization procedure, or masking implementation is 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: The novel OPV2-c2 candidate was prioritized so the first 100 OPV-vaccinated participants were randomly assigned 1:1 to Groups 3 and 4 to receive novel OPV2-c2. The second 100 OPV-vaccinated participants were randomly assigned 1:1 to Groups 1 and 2 to receive novel OPV2-c1. IPV-vaccinated adults were enrolled in parallel and randomly assigned 2:1 to Group 6 or Group 7 until Group 6 enrollment was complete, when 2:1 randomization was continued for Group 5 and Group 7.
Only the first 6 of 7 groups are shown.
Overall Study
| Stage | Group 1: OPV-vaccinated - One Dose of Novel OPV2 Candidate 1 | Group 2: OPV-vaccinated - Two Doses of Novel OPV2 Candidate 1 | Group 3: OPV-vaccinated - One Dose of Novel OPV2 Candidate 2 | Group 4: OPV-vaccinated - Two Doses of Novel OPV2 Candidate 2 | Group 5: IPV-vaccinated - Two Doses of Novel OPV2 Candidate 1 | Group 6: IPV-vaccinated - Two Doses of Novel OPV2 Candidate 2 |
|---|---|---|---|---|---|---|
| STARTED | 50 | 50 | 50 | 50 | 17 | 16 |
| Received First Dose of Vaccine | 50 | 50 | 50 | 50 | 17 | 16 |
| Received Second Dose of Vaccine | 0 | 49 | 0 | 49 | 17 | 15 |
| COMPLETED | 50 | 50 | 50 | 50 | 17 | 16 |
| NOT COMPLETED | 0 | 0 | 0 | 0 | 0 | 0 |
Analysis population for the primary outcome, as defined in the registry: The total vaccinated (TV) population includes all randomized participants who received at least one dose of study vaccine.
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.
Population: All enrolled participants
Only the first 6 of 8 groups are shown.
| Characteristic | Unit | Group 1: OPV-vaccinated - One Dose of Novel OPV2 Candidate 1 | Group 2: OPV-vaccinated - Two Doses of Novel OPV2 Candidate 1 | Group 3: OPV-vaccinated - One Dose of Novel OPV2 Candidate 2 | Group 4: OPV-vaccinated - Two Doses of Novel OPV2 Candidate 2 | Group 5: IPV-vaccinated - Two Doses of Novel OPV2 Candidate 1 | Group 6: IPV-vaccinated - Two Doses of Novel OPV2 Candidate 2 |
|---|---|---|---|---|---|---|---|
| Participants analysed | 50 | 50 | 50 | 50 | 17 | 16 | |
| Age, Continuous | years | 31 (SD 10) | 31 (SD 10) | 32 (SD 10) | 34 (SD 10) | 23 (SD 10) | 31 (SD 9) |
| Sex: Female, Male: Female | Participants | 22 | 29 | 28 | 32 | 11 | 13 |
| Sex: Female, Male: Male | Participants | 28 | 21 | 22 | 18 | 6 | 3 |
| Race/Ethnicity, Customized: White | Participants | 49 | 49 | 49 | 49 | 16 | 16 |
| Race/Ethnicity, Customized: Asian | Participants | 0 | 0 | 1 | 0 | 0 | 0 |
| Race/Ethnicity, Customized: Black or African American | Participants | 0 | 0 | 0 | 0 | 0 | 0 |
| Race/Ethnicity, Customized: Other | Participants | 1 | 1 | 0 | 1 | 1 | 0 |
| Number of Prior OPV Vaccinations: None | Participants | 0 | 0 | 0 | 0 | 17 | 16 |
| Number of Prior OPV Vaccinations: Three | Participants | 49 | 50 | 41 | 40 | 0 | 0 |
| Number of Prior OPV Vaccinations: Four | Participants | 1 | 0 | 9 | 9 | 0 | 0 |
| Number of Prior OPV Vaccinations: Five | Participants | 0 | 0 | 0 | 1 | 0 | 0 |
| Number of Prior IPV Vaccinations: None | Participants | 46 | 49 | 48 | 47 | 0 | 0 |
| Number of Prior IPV Vaccinations: One | Participants | 4 | 1 | 2 | 3 | 0 | 0 |
| Number of Prior IPV Vaccinations: Four | Participants | 0 | 0 | 0 | 0 | 6 | 4 |
| Number of Prior IPV Vaccinations: Five | Participants | 0 | 0 | 0 | 0 | 10 | 5 |
| Number of Prior IPV Vaccinations: Six or more | Participants | 0 | 0 | 0 | 0 | 1 | 7 |
6. Primary Endpoint
The registry lists the primary outcome as Number of Participants With Serious Adverse Events (SAEs) and Severe Adverse Events, measured over Up to 42 days after each vaccination.
| 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 serious adverse events and severe adverse events. An SAE is defined by its consequences or clinical importance: it may involve death, a life-threatening event, inpatient hospitalization or its prolongation, persistent or significant disability or incapacity, a congenital anomaly or birth defect, or another medically important event. A severe adverse event is defined by its effect on daily functioning: it prevents normal everyday activities and is not classified as an SAE.
These categories capture different aspects of harm. Seriousness is based on specified outcomes or medical importance, whereas severity in this registry definition is based on interference with everyday activities. An event can therefore be serious without being described as severe under this particular definition, and a severe event need not meet an SAE criterion. Keeping the categories distinct avoids treating them as interchangeable labels.
Counting participants with events is useful for describing how many people in each group experienced an event during the stated follow-up. It does not, by itself, describe event duration, recurrence, intensity beyond the definitions, or the time until an event. Nor does a count establish whether a vaccine caused an event. The registry’s separate definition of a related event relies on the investigator’s judgment that the event was probably or possibly caused by study vaccine, based on temporal association or lack of attribution to other conditions.
The endpoint’s timeframe is up to 42 days after each vaccination. The record does not report a single combined comparative result for serious and severe events, so the posted group counts should be read as descriptive safety information rather than as a complete estimate of a treatment contrast.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The posted serious-event counts are low in several groups, but the groups are not all the same size and their vaccination histories and dose schedules differ. Among OPV-vaccinated participants, the serious-event count was 1 among 50 at risk for one dose of candidate 1, 1 among 50 for two doses of candidate 1, 0 among 50 for one dose of candidate 2, and 1 among 50 for two doses of candidate 2. Among IPV-vaccinated participants, the count was 0 among 17 for two doses of candidate 1, 1 among 16 for two doses of candidate 2, and 0 among 17 for two doses of placebo. No deaths are recorded in any of these groups.
The record also lists counts for other affected participants: 44 among 50, 48 among 50, 47 among 50, 47 among 50, 17 among 17, 15 among 16, and 17 among 17, respectively, across the groups as described. Those counts should not be relabeled as severe events unless their category is explicitly established. The primary endpoint includes both SAEs and severe adverse events, but the registry record does not provide a single combined result that resolves how the categories contribute to that endpoint.
Influenza Like Illness is listed among the top serious terms at 6.2%; Crohn's Disease, Vomiting, and Anaphylactic Reaction are each listed at 2.0%. These entries describe the terms and percentages recorded, but the registry excerpt does not state the denominator or additional detail needed to interpret those percentages as group-specific risks. They should not be used to rank candidate groups or infer causation.
Small event counts are compatible with substantial uncertainty about the underlying frequency of uncommon events. A zero count means no such event was recorded in that group during the stated observation period; it does not establish that the true risk is zero. Similarly, a count of one does not demonstrate a difference between groups. A comparison would require a defined estimand, an analysis method, and uncertainty measures, none of which are reported for the primary outcome as one consolidated comparison.
The registry’s outcome information also includes immunogenicity measures, but their numerical results are not reported in the registry record. Consequently, these safety counts cannot support conclusions about antibody response or seroprotection. They describe recorded events within the specified study groups and follow-up, not definitive evidence of comparative safety or vaccine effect.
9. Statistical Methods Explained
Statistical interpretation begins by identifying what is being counted and the population to which the count applies. The primary outcome is a participant count, not an event rate over person-time. Its stated population is the total vaccinated population, defined as randomized participants who received at least one dose of study vaccine. The group figures pair affected-participant counts with participants at risk, allowing the reader to see the count in relation to the group’s recorded denominator without turning it into a new estimate.
What does a participant count capture?
A participant count records whether people experienced an event according to the endpoint definition. It is different from counting every occurrence: one participant may have more than one event, but a participant-based endpoint does not necessarily display the number of occurrences. The posted information does not give event-level timelines, recurrence, or person-time, so those features cannot be reconstructed from the counts.
The SAE definition uses consequences and clinical importance, while the severe-event definition uses interference with normal everyday activities and excludes events classified as SAEs. This distinction matters because seriousness and severity are not identical statistical categories. Combining them could conceal which criterion an event met. The record names the primary endpoint as participants with SAEs and severe adverse events, but the results do not present a single combined group comparison. That limits interpretation of the primary endpoint as a unified measure.
Why do denominators matter?
A count should be read alongside its at-risk group size. The groups have different denominators, and an identical count would not represent the same observed proportion in groups of different sizes. A proportion can be calculated from a count and denominator, but no additional proportions should be inferred beyond those explicitly recorded. Even a correctly calculated proportion would remain an estimate based on the observed participants; it would not remove uncertainty about the underlying frequency.
For uncommon outcomes, a small number of observed events gives limited information about the range of plausible underlying event frequencies. A confidence interval, when reported, expresses statistical uncertainty around an estimate under the assumptions of the analysis. The registry record does not report confidence intervals for the primary endpoint. Without them, the precision of comparative estimates cannot be assessed from the posted counts alone. General statistical principle: lack of an observed event in a group does not prove that the event cannot occur.
What can a comparison establish?
A randomized design can support comparisons between assigned groups when the comparison, analysis population, and statistical method are specified and when follow-up and outcome ascertainment are appropriately handled. Randomization does not make the observed counts self-interpreting. Here the groups include different prior vaccination backgrounds and dose schedules, and the primary outcome spans multiple categories and time points. The record’s note indicates that this endpoint was not reduced to one comparison. The registry record does not report a primary comparative estimate, hypothesis test, confidence interval, or statistical model for it.
General statistical principle: a p-value, if available, would describe how compatible the observed data are with a specified null model under its assumptions. It would not measure clinical importance, prove causality, or state the probability that a hypothesis is true. No primary-outcome p-value is reported in the registry record, so no significance claim is warranted.
How should planning illustrations be understood?
Planning calculations based on an observed effect are not the trial’s original design justification and are not observed power. The registry record describes an illustration using a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation, with a target effect defined as a stated fraction of the observed effect. For non-time-to-event outcomes, such illustrations are expressed as participants per arm for a specified power; time-to-event illustrations instead concern total events. The record does not include numerical planning results in the information available for this interpretation. These calculations therefore cannot be used to describe the trial’s achieved power or establish that its enrollment was adequate for a particular comparison.
Over-dispersion is relevant generally when count data vary more than a chosen model expects; ignoring it can make uncertainty appear too small. It is not possible to assess over-dispersion for this endpoint from participant counts alone, and the registry record does not report a count model or dispersion parameter. Likewise, the record does not report whether any adjustment for baseline factors was used. The most defensible reading is descriptive: the observed counts and denominators characterize the posted groups, while inferential and model-based conclusions remain unavailable.
10. Multiplicity, Missing Data and Analysis Populations
The study includes several outcomes: the registry lists 13 outcome measures and 12 analyses. These include safety measures, laboratory abnormalities, antibody titers, and seroprotection. When a study assesses many outcomes or comparisons, the chance of at least one apparently notable result can increase if each is interpreted without regard to the full testing plan. General statistical approaches can address multiplicity by prioritizing outcomes, adjusting inference, or interpreting results as exploratory. Which approach was planned or used is not reported in the registry record.
The primary outcome includes more than one adverse-event category and is observed across follow-up up to 42 days after each vaccination. The record indicates that it was not reduced to one comparison. It does not report a hierarchy among categories or time points, an adjustment for multiple comparisons, interim analyses, or a statistical analysis plan. These details should not be inferred from the Phase 2 designation or from the listed outcomes.
Missing-data handling is also not reported in the registry record. The record defines the total vaccinated population, but it does not describe how missing safety assessments, incomplete follow-up, withdrawals, or unavailable laboratory measurements were treated. The number of participants at risk is listed for the safety groups, but that alone does not explain whether all participants contributed equally across the full follow-up period.
The registry record does not report an intention-to-treat analysis definition, a per-protocol population, or a detailed method for handling participants who did not receive all planned doses. The stated total vaccinated population includes randomized participants who received at least one dose; this definition should not be assumed to apply to every secondary outcome. Without analysis-population and missing-data details, it is difficult to determine how fully the reported groups represent all randomized participants or how incomplete observations may affect results.
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 |
|---|---|---|---|
| Group 1: OPV-vaccinated - One Dose of Novel OPV2 Candidate 1 | 1 | 50 | 2.0% |
| Group 2: OPV-vaccinated - Two Doses of Novel OPV2 Candidate 1 | 1 | 50 | 2.0% |
| Group 3: OPV-vaccinated - One Dose of Novel OPV2 Candidate 2 | 0 | 50 | 0.0% |
| Group 4: OPV-vaccinated - Two Doses of Novel OPV2 Candidate 2 | 1 | 50 | 2.0% |
| Group 5: IPV-vaccinated - Two Doses of Novel OPV2 Candidate 1 | 0 | 17 | 0.0% |
| Group 6: IPV-vaccinated - Two Doses of Novel OPV2 Candidate 2 | 1 | 16 | 6.2% |
| Group 7: IPV-vaccinated - Two Doses of Placebo | 0 | 17 | 0.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Group 1: OPV-vaccinated - One Dose of Novel OPV2 Candidate 1 | 0 of 50 |
| Group 2: OPV-vaccinated - Two Doses of Novel OPV2 Candidate 1 | 0 of 50 |
| Group 3: OPV-vaccinated - One Dose of Novel OPV2 Candidate 2 | 0 of 50 |
| Group 4: OPV-vaccinated - Two Doses of Novel OPV2 Candidate 2 | 0 of 50 |
| Group 5: IPV-vaccinated - Two Doses of Novel OPV2 Candidate 1 | 0 of 17 |
| Group 6: IPV-vaccinated - Two Doses of Novel OPV2 Candidate 2 | 0 of 16 |
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 |
|---|---|
| Group 1: OPV-vaccinated - One Dose of Novel OPV2 Candidate 1 | 44 of 50 |
| Group 2: OPV-vaccinated - Two Doses of Novel OPV2 Candidate 1 | 48 of 50 |
| Group 3: OPV-vaccinated - One Dose of Novel OPV2 Candidate 2 | 47 of 50 |
| Group 4: OPV-vaccinated - Two Doses of Novel OPV2 Candidate 2 | 47 of 50 |
| Group 5: IPV-vaccinated - Two Doses of Novel OPV2 Candidate 1 | 17 of 17 |
| Group 6: IPV-vaccinated - Two Doses of Novel OPV2 Candidate 2 | 15 of 16 |
Most frequent serious adverse event terms
| Event term | Organ system | Group 1: OPV-vaccinated - One Dose of Novel OPV2 Candidate 1 | Group 2: OPV-vaccinated - Two Doses of Novel OPV2 Candidate 1 | Group 3: OPV-vaccinated - One Dose of Novel OPV2 Candidate 2 | Group 4: OPV-vaccinated - Two Doses of Novel OPV2 Candidate 2 | Group 5: IPV-vaccinated - Two Doses of Novel OPV2 Candidate 1 | Group 6: IPV-vaccinated - Two Doses of Novel OPV2 Candidate 2 |
|---|---|---|---|---|---|---|---|
| Crohn's Disease | Gastrointestinal disorders | 1 of 50 | 0 of 50 | 0 of 50 | 0 of 50 | 0 of 17 | 0 of 16 |
| Vomiting | Gastrointestinal disorders | 0 of 50 | 1 of 50 | 0 of 50 | 0 of 50 | 0 of 17 | 0 of 16 |
| Anaphylactic Reaction | Immune system disorders | 0 of 50 | 0 of 50 | 0 of 50 | 1 of 50 | 0 of 17 | 0 of 16 |
| Influenza Like Illness | General disorders | 0 of 50 | 0 of 50 | 0 of 50 | 0 of 50 | 0 of 17 | 1 of 16 |
Most frequent non-serious adverse event terms
| Event term | Organ system | Group 1: OPV-vaccinated - One Dose of Novel OPV2 Candidate 1 | Group 2: OPV-vaccinated - Two Doses of Novel OPV2 Candidate 1 | Group 3: OPV-vaccinated - One Dose of Novel OPV2 Candidate 2 | Group 4: OPV-vaccinated - Two Doses of Novel OPV2 Candidate 2 | Group 5: IPV-vaccinated - Two Doses of Novel OPV2 Candidate 1 | Group 6: IPV-vaccinated - Two Doses of Novel OPV2 Candidate 2 |
|---|---|---|---|---|---|---|---|
| Headache | Nervous system disorders | 11 of 50 | 14 of 50 | 16 of 50 | 14 of 50 | 6 of 17 | 5 of 16 |
| Upper Respiratory Tract Infection | Infections and infestations | 9 of 50 | 4 of 50 | 7 of 50 | 13 of 50 | 0 of 17 | 5 of 16 |
| Oropharyngeal Pain | Respiratory, thoracic and mediastinal disorders | 3 of 50 | 8 of 50 | 7 of 50 | 5 of 50 | 3 of 17 | 1 of 16 |
| Diarrhoea | Gastrointestinal disorders | 4 of 50 | 3 of 50 | 3 of 50 | 6 of 50 | 6 of 17 | 3 of 16 |
| Blood Creatine Phosphokinase Increased | Investigations | 3 of 50 | 5 of 50 | 4 of 50 | 5 of 50 | 1 of 17 | 0 of 16 |
| Nasopharyngitis | Infections and infestations | 4 of 50 | 4 of 50 | 1 of 50 | 2 of 50 | 5 of 17 | 1 of 16 |
| Hypophosphataemia | Metabolism and nutrition disorders | 2 of 50 | 4 of 50 | 3 of 50 | 5 of 50 | 0 of 17 | 2 of 16 |
| Abdominal Pain | Gastrointestinal disorders | 0 of 50 | 3 of 50 | 3 of 50 | 4 of 50 | 1 of 17 | 2 of 16 |
| Nasal Congestion | Respiratory, thoracic and mediastinal disorders | 1 of 50 | 3 of 50 | 3 of 50 | 3 of 50 | 0 of 17 | 1 of 16 |
| Dizziness | Nervous system disorders | 0 of 50 | 2 of 50 | 2 of 50 | 2 of 50 | 0 of 17 | 4 of 16 |
Serious events with the highest arm-level rate: influenza like illness (6.2%), crohn's disease (2.0%), vomiting (2.0%), anaphylactic reaction (2.0%).
For the serious-event figures, read each group’s affected count together with its stated at-risk count. The OPV-vaccinated groups report serious-event counts of 1 among 50, 1 among 50, 0 among 50, and 1 among 50, in the order of the candidate and dose schedules described. The IPV-vaccinated groups report 0 among 17, 1 among 16, and 0 among 17 for candidate 1, candidate 2, and placebo. The registry records no deaths in any group.
The record separately reports other affected-participant counts for each group. These are not interchangeable with the serious-event counts, and the available descriptions do not establish that the “other” category is exactly the primary endpoint’s severe-event component. The primary endpoint includes SAEs and severe adverse events, so a complete reading would require clarity about how these categories were tabulated together.
These are descriptive counts, not proof that an event was caused by a study vaccine. The registry defines relatedness as an investigator judgment of probable or possible relationship based on temporal association or attribution to other conditions, but group-specific related-event results are not reported in the registry record. A zero count is limited to the events recorded in that group during follow-up; it is not evidence that an event is impossible or that groups are equivalent.
12. What the Result Does, and Does Not, Mean
The posted results establish that the registry records serious adverse-event counts for each study group, along with other affected-participant counts and no deaths. They also show that serious-event counts were low in the listed groups during follow-up up to 42 days after each vaccination. These observations describe what was recorded among the participants at risk; they do not by themselves establish comparative safety, causal attribution, or the absence of uncommon harms.
The study’s randomized design and placebo group are relevant features for comparative evaluation, but the registry record does not report a single primary-endpoint comparison, its uncertainty, or a statistical test. The groups also differ in prior vaccination status and dose schedule. A simple comparison across all groups would therefore not answer one clearly defined question without specifying which population, schedule, outcome category, and contrast are intended.
The record identifies immunogenicity as an objective and lists antibody and seroprotection outcomes. Their numerical results are not reported in the registry record. The safety counts therefore cannot be used to infer antibody responses or seroprotection. Nor can a planning illustration based on observed effects be interpreted as evidence of observed power; it is a planning calculation, not a result about the trial’s actual ability to detect an effect.
In general, a statistical estimate is more informative when paired with a measure of uncertainty and a clearly stated analysis population. Those elements help distinguish a small observed count from a precisely estimated low frequency. Such comparative estimates and uncertainty measures for the primary endpoint are not reported in the registry record. The appropriate interpretation is consequently restrained: the listed counts describe the recorded safety experience in the specified groups, while broader claims about differences between candidates, vaccine schedules, placebo, or historical controls are not established by these figures alone.
13. Why This Trial Matters Statistically
This trial is statistically notable because its safety question spans multiple groups formed by prior vaccination history, candidate vaccine, and dose schedule. OPV-vaccinated participants were studied with one-dose and two-dose schedules for both candidates, while IPV-vaccinated participants were studied with two-dose schedules and a placebo group. That structure makes it important to define the comparison before interpreting any difference in counts.
The endpoint also combines concepts that should remain distinct. Seriousness is defined by specified consequences or medical importance, whereas severity is defined by prevention of normal everyday activities and exclusion of SAEs. A combined endpoint may be useful for broad safety monitoring, but its interpretation depends on understanding the contribution of each category. The registry record does not provide one consolidated comparative result for the primary endpoint.
Small safety counts are a reminder that descriptive results and inferential results answer different questions. Counts reveal what was observed; uncertainty estimates and a clearly specified analysis help show how much those observations can support about underlying group differences. The posted record reports group counts and denominators, but not the primary endpoint’s comparative estimate or its precision.
The study also lists immunogenicity outcomes alongside safety outcomes. Keeping those outcome families separate is essential: safety observations do not substitute for antibody or seroprotection results. The registry record’s missing numerical immunogenicity results and unreported analysis details limit the statistical conclusions that can be drawn. The value of the record is its description of the randomized study structure and observed safety counts, together with a clear indication of what remains unresolved for comparative interpretation.
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 does not report a consolidated estimate comparing groups for the primary outcome, nor does it report confidence intervals or a primary-outcome test. The primary endpoint combines serious and severe adverse events, but the available group counts do not clarify how the severe-event component contributes to a combined result. This prevents a complete quantitative interpretation of the endpoint as named.
The groups differ by prior OPV or IPV vaccination and by candidate and dose schedule. Comparisons across these groups therefore do not isolate a single factor unless a specific contrast and analysis are defined. The official title mentions historical controls given Sabin OPV2 or placebo, but details and results for those controls are not reported in the registry record.
The record identifies the total vaccinated population but does not report detailed missing-data procedures, follow-up completeness, or analysis populations for each outcome. It also does not report the statistical analysis plan, multiplicity handling, interim analyses, or the method used to analyze the primary endpoint. The registry lists quadruple masking, while the official title describes partial blind; the record does not explain the relationship between those descriptions.
Immunogenicity outcomes are listed, but their numerical results are not reported in the registry record. The adverse-event information also does not provide event-level timing, recurrence, or group-specific relatedness results. These limitations mean that the posted safety counts should not be extended into claims about vaccine causation, comparative efficacy, or the frequency of events beyond the recorded follow-up and population.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: A Phase 2 Study to Evaluate the Safety and Immunogenicity of Two Oral Poliovirus Vaccine Candidates — NCT04544787.
- Registry record last updated 2021-10-15; status last verified 2021-09.
- Results first posted 2021-10-15.
- 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
NCT04544787 is a completed randomized Phase 2 multicenter study of two novel live attenuated serotype 2 oral poliovirus vaccine candidates in healthy adults previously vaccinated with OPV or IPV. It records quadruple masking, while the official title describes partial blind. The study enrolled 250, began on 2018-10-22, and had a primary completion date of 2019-01-31.
OPV-vaccinated participants received one or two doses of either candidate; IPV-vaccinated participants received two doses of either candidate or placebo. The primary outcome was the number of participants with SAEs and severe adverse events up to 42 days after each vaccination. The registry reports group-level serious and other affected-participant counts and no deaths. It does not report a consolidated primary comparison or numerical immunogenicity results. Interpretation is therefore limited to the descriptive safety information and the study structure recorded in the registry.