Phase 1 Novel Live Attenuated Serotype 2 Oral Polio Vaccine Study in Inactivated Polio Vaccine (IPV) Primed Adults: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Phase 1 Novel Live Attenuated Serotype 2 Oral Polio Vaccine Study in Inactivated Polio Vaccine (IPV) Primed Adults (NCT03430349), a randomized phase 1 study. The primary outcome is Number of Participants With Serious Adverse Events and Severe Adverse Events Throughout the Study.

2. Clinical Question

This was a first-in-human Phase 1 study conducted in contained conditions. Its stated purpose was to evaluate safety, immunogenicity, shedding, and genetic stability for two novel oral polio vaccine type 2 candidates in IPV-primed adults before further testing in other populations. The primary outcome concerns adverse events, not an estimate of vaccine efficacy. Secondary outcomes listed in the record include antibody titers, seroprotection, seroconversion, adverse events, laboratory deviations, and a mouse neurovirulence measure.

The central statistical question is descriptive: what adverse-event counts were recorded in each candidate group during the stated follow-up? The registry record does not report a comparative statistical estimate for the primary outcome, so the counts do not establish whether one candidate differs from the other.

3. Trial Design

This was a Phase 1, randomized, triple-masked, single-center study with a sequential model. The registry status is completed. It lists an enrollment of 30 and describes two groups: Novel OPV2 Candidate 1 and Novel OPV2 Candidate 2. Each group is listed with 15 participants at risk for serious and other adverse events.

Participants were healthy adults previously primed with IPV. Each group received one oral vaccination on study Day 0. Both candidate descriptions specify six drops, 0.3 mL total, and approximately 10⁶ CCID50. The record identifies no placebo or no-vaccine group. Consequently, the posted group counts compare the two candidates, while the design does not provide a concurrent untreated group for interpreting events that might also occur without vaccination.

The primary outcome covers serious and severe adverse events from Day 0 up to 42 days. The record defines serious events by outcomes such as death, life-threatening illness, hospital admission, or notable incapacity. It defines severe events as events that prevent normal everyday activities or fever > 39°C, and specifies that this category does not include serious events. Solicited events were captured using a predefined diary checklist or temperature measurement for up to 7 days after vaccination; unsolicited events were recorded through the end of the study.

The brief summary describes safety, immunogenicity, shedding, and genetic stability as study aims. The registry lists secondary outcomes in these areas, but the record does not report results for all those outcomes in the material relevant to this primary safety interpretation. Details of the randomization procedure, masking implementation, allocation sequence, and the schedule implied by the sequential model 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: Participants were enrolled sequentially into one of two groups, and received a single dose of one of two novel oral polio vaccine type 2 (nOPV2) candidates. Participants were monitored for adverse events, immune responses, and fecal shedding of the vaccine virus for 28 days. If if shedding continued beyond 28 days participants were asked to further collect stool samples daily on an ambulatory basis until end of shedding.

Overall Study

Analysis population for the primary outcome, as defined in the registry: All randomized participants who received a 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 randomized participants who received a dose of study vaccine.

6. Primary Endpoint

The registry lists the primary outcome as Number of Participants With Serious Adverse Events and Severe Adverse Events Throughout the Study, measured over From Day 0 up to 42 days.

The primary endpoint is the number of participants with serious adverse events and severe adverse events during the period from Day 0 up to 42 days. It is a participant-count endpoint: it concerns whether participants experienced events, rather than the total number of separate episodes. The record identifies the analysis population as all randomized participants who received a dose of study vaccine.

Serious and severe are not interchangeable categories in this definition. Serious events are identified by their consequences, including death, life-threatening events, hospital admission, or notable incapacity. Severe events are defined by disruption of normal everyday activities or fever > 39°C; the record explicitly excludes serious events from the severe category. Solicited and unsolicited events may both contribute to the primary outcome. Solicited events use predefined symptoms or fever reporting during up to 7 days after vaccination, while unsolicited events are recorded through study end.

A participant-count endpoint is useful in an early-phase safety study because it describes how many people experienced events of interest during follow-up. It can make event occurrence easier to interpret than an event total when individuals could experience more than one event. However, counts alone do not describe timing, duration, recurrence, or severity beyond the categories explicitly defined. The posted results do not give a separate severe-event count, so the serious-event figures alone cannot establish the full primary endpoint count.

The investigator assessed event causality as unrelated, unlikely, possibly, or probably related to vaccination. The registry record does not report category-specific results for those causality assessments.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

A participant-count outcome is a binary outcome at the participant level: a person either meets the specified event definition during the stated follow-up or does not. This is different from counting every event episode. If a participant has repeated events, a participant-count endpoint does not necessarily represent that repetition unless the outcome definition separately records event totals. The primary outcome is framed as the number of participants with serious and severe adverse events, while the posted counts distinguish serious events from other adverse events.

What does randomization contribute?

Randomization is intended, in general, to make treatment groups comparable with respect to measured and unmeasured characteristics at allocation, on average. It does not guarantee that two small groups will be identical in every characteristic. Nor does randomization remove uncertainty from a small study or correct incomplete outcome reporting. The registry says allocation was randomized, but details of the sequence generation and implementation are not reported in the registry record.

The trial is described as triple-masked. Masking can, in general, reduce the influence of treatment knowledge on participant reporting, investigator assessment, and other study processes, depending on who is masked and how the masking is maintained. The registry does not identify the masked parties or describe how masking was implemented, so those operational details cannot be evaluated from the record.

How should counts be compared?

For a binary participant-level outcome, a direct comparison could describe event proportions or estimate a between-group contrast. Such a comparison would ordinarily need to identify the event definition, analysis population, denominators, missing-outcome handling, and statistical method. The registry reports group counts and at-risk denominators for serious and other adverse events, but no comparative analysis is reported. No p-value, confidence interval, or model-based estimate is posted for the primary outcome.

General statistical interpretation requires separating the observed count from the uncertainty about the underlying event risk. A count of zero is an observation in a particular group over a particular follow-up period; it is not proof that an event cannot occur. A comparative estimate would also need uncertainty information, especially when event counts are sparse or absent. The registry does not report such an estimate, so the reader should not infer equivalence or a statistically established difference from the matching serious-event counts.

Why do event definitions matter?

Here, serious events are defined by consequential outcomes, whereas severe events are defined by interference with normal activities or fever > 39°C and explicitly exclude serious events. This separation means that a serious-event count is not a complete substitute for the severe-event count. “Other adverse events” is a separate label in the posted group data; the registry does not identify it as a count of severe events. Counts should therefore be interpreted using the labels and definitions actually reported rather than treating all non-serious events as severe or all adverse events as meeting the primary endpoint.

Adverse-event ascertainment also differs by reporting route and period. Solicited signs and symptoms were collected using a predefined checklist or temperature measurement for up to 7 days after vaccination. Unsolicited events were recorded through the end of the study. The primary endpoint follow-up is stated as Day 0 up to 42 days. General interpretation should take account of such differences in how information is elicited, because a predefined checklist and open-ended reporting can capture events differently. The registry does not give the event-level data needed to examine those patterns.

What do the planning assumptions mean?

The stated sample-size assumptions describe a planning illustration based on the observed effect, with a two-sided significance level of 0.05, equal allocation, and a normal approximation. The illustration considers the effect to detect as a stated fraction of the observed effect. Such a calculation is conditional on its assumptions and is useful for thinking about the size of a future study under a chosen target effect. It is not a measure of the probability that the completed trial detected an effect, and it should not be called observed power.

Planning calculations based on an observed effect can be especially unstable when the estimate comes from a small early-phase study or sparse event counts. General statistical practice treats the chosen target effect, allocation, significance level, and approximation as assumptions rather than details about the precision of the current results. The registry record does not report the original sample-size justification, so the planning illustration should not be attributed to the trial’s design process.

More broadly, a statistical plan would ordinarily specify how the primary endpoint is analyzed, how missing observations are handled, how any multiplicity is addressed, and what analysis populations are used. Those details are not reported in the registry record. Since the registry lists no analyses, it is not possible to determine whether any unposted analysis used adjustment, stratification, or another method.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists a primary safety outcome and multiple secondary outcomes, including solicited and unsolicited adverse events, clinically relevant laboratory deviations, antibody titers, seroprotection, seroconversion, and a mouse neurovirulence assessment. When a study examines multiple outcomes, general statistical practice recognizes that the chance of at least one apparently unusual result may increase if each is tested separately without a prespecified strategy. The registry record does not report a multiplicity plan, such as a hierarchy or adjustment procedure. No claim about how multiplicity was handled can therefore be made.

The registry reports no analyses. It does not provide a statistical analysis plan, a list of planned comparisons, or results for all listed outcomes. The number and ordering of analyses, any interim analyses, and any adjustment for repeated looks are not reported in the registry record. No interim analysis should be inferred from the sequential-model label alone.

The primary outcome population is described as randomized participants who received a dose of study vaccine. This is not, by itself, a full account of every analysis population. The registry record does not report whether there were exclusions, whether all randomized participants were included in other analyses, or how protocol deviations were treated.

Missing-data methods and the extent of missing outcome information are not reported in the registry record. The posted at-risk counts give denominators for the listed adverse-event summaries, but they do not explain whether any observations were unavailable, how follow-up completion was assessed, or how any missing records were handled. A reader should not assume that missing outcomes were absent, imputed, or excluded by a particular rule. Without those details, the robustness of the results to missingness cannot be assessed.

11. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

Most frequent non-serious adverse event terms

For Novel OPV2 Candidate 1, the registry lists 0 serious adverse events among 15 participants at risk and 15 participants with other adverse events. For Novel OPV2 Candidate 2, it likewise lists 0 serious adverse events among 15 participants at risk and 15 participants with other adverse events. The death count is 0 in each group.

These counts describe the safety summaries recorded for the stated follow-up, from Day 0 up to 42 days for the primary outcome. They do not mean that 15 severe events occurred in either group. The record gives no separate severe-event count, and the category “other adverse events” is not defined as equivalent to severe events. The primary outcome also includes both solicited and unsolicited events, while the reported group fields do not give a separate breakdown by those categories.

The registry record lists no top serious-event terms. It does not provide event-level descriptions or causality-category counts, despite describing the investigator’s causality assessment categories. Consequently, the posted summaries cannot establish the nature, timing, duration, or assessed relationship to vaccination of the other events.

Zero serious events in both groups is a descriptive finding, not a statistical demonstration that serious-event risk is absent or that the candidates have identical safety profiles. No confidence interval or comparative analysis is reported.

12. What the Result Does, and Does Not, Mean

The results support a narrow descriptive statement: the registry lists no serious adverse events and no deaths in either candidate group during the reported safety follow-up, and it lists 15 participants with other adverse events in each group. These counts apply to the group denominators and outcome labels recorded in the registry. They do not establish that serious events cannot occur, that the two candidates have equal risks, or that all adverse events were mild.

The primary endpoint combines serious and severe adverse-event concepts, but the posted results do not report a distinct severe-event count. Because severe events are specifically defined as excluding serious events, the serious-event counts alone do not give the total number meeting the primary endpoint definition. The other-adverse-event counts cannot fill that gap without a clear mapping to the severe-event category, which is not reported.

The study was designed as an early-phase evaluation in healthy adults previously primed with IPV. Its stated aims extend beyond safety to immunogenicity, shedding, and genetic stability. The registry lists secondary outcomes related to these aims, but the safety counts do not answer those questions. No conclusion about antibody response, shedding, genetic stability, or neurovirulence results follows from the adverse-event summaries.

No comparative statistical analysis is reported. Thus, the equal serious-event counts should not be described as evidence of equivalence, and no statistical significance conclusion can be drawn. In general, a formal comparison requires an estimate and uncertainty assessment; neither is posted for the primary endpoint.

The record also does not report a complete statistical plan, missing-data handling, or an explanation of the planned enrollment. These absences limit assessment of how the study’s design and analysis relate to the stated questions. The findings are best treated as short-term, descriptive safety information for the enrolled population and the two candidate groups, with the limitations of the reported outcome detail kept explicit.

13. Why This Trial Matters Statistically

Early-phase randomized studies can produce useful descriptive information before a candidate is tested in larger or different populations. In this study, random allocation and masking are part of the design, and the record states that the work was conducted in healthy adults previously primed with IPV. The primary outcome also specifies a follow-up period and distinguishes serious from severe events. Those features give a framework for interpreting the safety counts.

The registry’s concise counts also illustrate why outcome labels matter. The listed serious-event counts are 0 in both groups, while the counts for other adverse events are 15 in both groups. Yet the primary outcome refers to serious and severe events, and no separate severe count is posted. Without a category-specific result, the apparent completeness of a participant count can be misleading: a reader may see counts for safety events but still lack the exact count required to interpret the stated endpoint.

This example also illustrates the difference between descriptive results and inferential claims. Matching observed counts do not establish that underlying risks are equal. A confidence interval or other uncertainty estimate would help describe how precisely a group contrast is known, but the registry reports no comparative analysis. The appropriate statistical reading is therefore limited to the observations and denominators recorded.

Finally, the study’s stated objectives encompass more than adverse events. The listed secondary outcomes indicate a broader evaluation of immune response, laboratory findings, and other characteristics. A registry record can identify these questions without reporting all the results or the methods used to analyze them. For clinical researchers, that distinction is important: an outcome list describes what was considered, whereas a result and its analysis are needed to assess what the data show.

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 results are restricted to the population described in the record: healthy adults previously primed with IPV. The stated study purpose places this evaluation before testing in other populations. The findings therefore do not directly describe outcomes in young children, infants, or the broader adult and adolescent populations mentioned in the brief summary.

The study is described as Phase 1, first-in-human, single-center, and conducted in contained conditions. Its enrollment is 30. These design features frame the scope of the evidence, but the registry does not report a sample-size justification or a statistical analysis plan. It is not possible to determine from the record what precision or power the investigators intended for the primary outcome.

The primary follow-up is from Day 0 up to 42 days. The record does not provide longer-term safety results. It also does not provide a distinct severe-event count, event-level descriptions, or counts by causality assessment. The listed other-adverse-event counts therefore offer limited detail for understanding what types of events occurred and whether they met the severe-event definition.

No comparative analysis is reported, and no confidence interval or p-value is available for the primary endpoint. The registry also does not report missing-data handling, details of the analysis population beyond its primary-outcome definition, or multiplicity procedures. These omissions prevent assessment of the precision and robustness of any candidate-to-candidate comparison.

The record describes triple masking and randomization but does not report the operational details of masking or allocation. The secondary outcomes listed in the registry also do not, on their own, establish which results were analyzed or how they were assessed. These limitations should be kept in view when interpreting the posted safety counts.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Phase 1 Novel Live Attenuated Serotype 2 Oral Polio Vaccine Study in Inactivated Polio Vaccine (IPV) Primed Adults — NCT03430349.
• Registry record last updated 2021-02-04; status last verified 2021-01.
• Results first posted 2021-02-04.
• 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.

18. Record Summary

The registry describes NCT03430349 as a completed, randomized, triple-masked, single-center Phase 1 study with a sequential model. It enrolled healthy adults previously primed with IPV and evaluated one oral vaccination with Novel OPV2 Candidate 1 or Novel OPV2 Candidate 2. The primary safety timeframe was from Day 0 up to 42 days.

The registry lists 0 serious adverse events and 0 deaths in each group, along with 15 participants with other adverse events in each group. It does not report a distinct severe-event count or a comparative analysis of the primary endpoint. The stated study aims include safety, immunogenicity, shedding, and genetic stability, with several secondary outcomes listed. Missing-data procedures, multiplicity handling, the statistical analysis plan, and the trial’s sample-size justification are not reported in the registry record.