Study to Evaluate the Safety, Tolerability, and Immunogenicity of an RNA Vaccine Candidate Against COVID-19 in Healthy Children: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Study to Evaluate the Safety, Tolerability, and Immunogenicity of an RNA Vaccine Candidate Against COVID-19 in Healthy Children (NCT04816643), a non-randomized phase 3 study. The primary outcome is Phase 1: Percentage of Participants With Local Reactions Within 7 Days After Dose 1: >=5 to <12 Years of Age.

2. Clinical Question

The registered primary outcome is descriptive: it concerns the frequency of local reactions after vaccination, rather than a direct comparison of vaccine and placebo. Reactions were collected in an electronic diary or during unscheduled clinical assessments from Day 1 to Day 7 after dose 1. The endpoint combines specified injection-site reactions, including pain, redness, and swelling, with grading rules for severity.

The study also covered safety, tolerability, and immune-response questions across age and dose groups. Its listed secondary outcomes include neutralizing antibody titers and fold rise at specified time points. Those additional questions are distinct from the primary local-reaction endpoint. The numerical primary result, including its confidence interval, is not reported in the registry record, so the stated question cannot be answered from the available primary-outcome entry.

3. Trial Design

The registry describes a pediatric study that proceeded through Phase 1, Phase 2, and Phase 3. Its brief summary calls it a Phase 1/2/3 study, while the phase classification identifies Phase 3. The official title describes Phase 1 as open-label dose-finding and Phase 2/3 as placebo-controlled and observer-blinded. However, the recorded allocation is non-randomized and the recorded masking is none. Those registry fields matter when judging whether treatment groups can be compared as if assigned by chance; the record does not establish a randomized comparison.

The study lists BNT162b2 dose levels of 3 mcg, 10 mcg, 20 mcg, and 30 mcg, along with placebo. Arm descriptions cover age bands from 6 months to <2 years, 2 to <5 years, 5 to <12 years, and 12 to <16 years for some groups. The Phase 1 primary endpoint is limited to participants aged ≥5 to <12 years and measures reactions after dose 1. Many arm descriptions refer to two doses 21 days apart; some listed groups have three-dose regimens. These differing arms and schedules mean that the study is not a single uniform comparison across all participants.

The registry reports enrollment of 11837 and a completed status. The start date is 2021-03-24, and the primary completion date is 2023-10-04. These record details describe the study’s scope and timing, but do not supply the missing primary endpoint estimate. The record also describes an assessment of safety and immunogenicity for participants younger than 6 months as potentially subsequent and dependent on data and benefit-risk assessment; it does not identify this as an evaluated arm in the listed results.

Because allocation is non-randomized, differences between arms could reflect differences in who entered each group, the age and dose structure, or other factors, as well as any treatment-related variation. The registry record does not report a basis for treating the listed arms as balanced groups. Accordingly, placebo’s presence in the study title and intervention list does not by itself establish a randomized treatment contrast.

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: Out of 11837 participants enrolled, 11760 were vaccinated.

Only the first 6 of 16 groups are shown.

Phase 1

Reasons for not completing this period:

Phase 2/3

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Safety population consisted of all participants who received at least 1 dose of study intervention. Participants were analyzed according to the treatment which they received.

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: Safety set included all participants who received at least 1 dose of the study intervention. Participants were analyzed according to the treatment which they received.

Only the first 6 of 17 groups are shown.

6. Primary Endpoint

The registry lists the primary outcome as Phase 1: Percentage of Participants With Local Reactions Within 7 Days After Dose 1: >=5 to <12 Years of Age, measured over Phase 1: From Day 1 to Day 7 after Dose 1.

The primary endpoint is the percentage of participants aged ≥5 to <12 years in Phase 1 who experienced a local reaction during the period from Day 1 to Day 7 after dose 1. Local reactions were recorded in an electronic diary or during unscheduled clinical assessments. The definition includes injection-site pain, redness, and swelling. Redness and swelling were graded using measured size, while pain was graded according to its effect on activity and need for emergency care or hospitalization. The record also includes reactions reported as adverse events within the same 7-day period.

This type of endpoint is used to describe the frequency of short-term local reactions following a dose. Reporting a percentage makes the result interpretable as a proportion of the safety population assessed for the outcome. A confidence interval conveys uncertainty around that estimated proportion; it is not a range containing a fixed share of individual participants’ reactions.

The registry specifies a two-sided 95% confidence interval using the Clopper and Pearson method. This is an exact binomial interval commonly used for proportions, including when event counts are small. The primary endpoint entry gives its definition and analysis population, but no observed percentage or confidence limits. The result is therefore not reported in the registry record, and the endpoint’s frequency and precision cannot be described from this entry.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does a percentage estimate? The primary outcome is a binary event measure: each participant either met the local-reaction definition during the specified follow-up period or did not. The percentage expresses the observed proportion in the endpoint’s analysis population. General explanation: a proportion is useful for describing event frequency, but it does not by itself show whether an event was caused by treatment or whether the frequency differs from another group.

The registry identifies the safety population as participants who received at least one dose, analyzed according to the treatment received. This is the stated population for the primary safety outcome. It is distinct from an intention-to-treat population, which generally follows assigned groups regardless of treatment received; the registry’s allocation is non-randomized, and the primary entry does not describe an intention-to-treat analysis.

What does the confidence interval add? The primary outcome uses a two-sided 95% confidence interval based on the Clopper and Pearson method. General explanation: a confidence interval describes the statistical uncertainty around an estimate under the assumptions of the method. Wider intervals indicate less precision, while narrower intervals indicate greater precision. The interval is not a guarantee that the true value lies within its limits, and it does not describe the range of reactions among individual participants. Since the estimate and interval are not reported in the registry record, their width and implications cannot be assessed.

The Clopper and Pearson method is an exact method for a binomial proportion. General explanation: exact methods can be useful when event counts are small or near the boundaries of possible proportions, where simple approximations may behave poorly. The method’s label does not establish that the estimate is precise; precision depends in part on the amount of information and the number of observed events. Neither the primary event count nor the endpoint denominator appears in the primary outcome entry.

How were reactions defined? Redness and swelling were measured and graded using the registry’s size thresholds. Pain categories were based on interference with activity and, for the most severe category, an emergency-room visit or hospitalization. Grade 4 reactions were classified by an investigator or medically qualified person. The endpoint also includes reactions recorded as adverse events in the case report form during the observation period. These rules make the outcome more operational than a broad report of “any reaction,” but they do not tell the reader how many reactions of each type occurred.

The record says reactions were collected by electronic diary or unscheduled clinical assessment. General explanation: outcome collection methods can affect completeness and comparability. A diary depends on participant or caregiver reporting, while an unscheduled assessment depends on seeking or receiving clinical evaluation. The registry entry does not report the proportion with completed diaries, procedures for reconciling sources, or rules for handling missing assessments. The possibility and effect of missing data therefore cannot be quantified from this record.

Why does allocation matter? The registry records non-randomized allocation and no masking. General explanation: randomization is intended to reduce systematic differences between treatment groups, and masking can reduce some measurement or reporting biases. In a non-randomized study, groups may differ before treatment or in how they are observed. This is particularly relevant when comparing age groups, dose groups, open-label groups, and placebo groups. The official title describes a placebo-controlled, observer-blinded Phase 2/3 study, but the recorded masking field is none; the registry information does not reconcile that wording with the field. It is therefore important not to assume that every listed contrast was blinded or randomized.

What about over-dispersion? General explanation: over-dispersion arises when observed variation is greater than a model assumes, often because observations are more heterogeneous or correlated than expected. It can make standard errors too small if the model does not account for that extra variation. The primary endpoint is specified as a participant-level percentage with a Clopper and Pearson interval, not as a count model, and the registry record does not describe a model-based over-dispersion adjustment. The concept is relevant generally, but there is no basis in this record to claim that over-dispersion was observed or affected the primary analysis.

How should planning calculations be understood? General explanation: sample-size calculations depend on assumptions about the effect to detect, significance level, allocation, and statistical approximation. The planning illustration described in the registry metadata uses a two-sided significance level of 0.05, equal allocation, a normal approximation, and an effect expressed as a fraction of an observed effect. Such figures are planning illustrations, not observed power and not evidence that the trial was designed with those assumptions. No resulting participant-per-arm values are included in this record, and the registry does not report the trial’s own sample-size justification.

General explanation: a p-value, when reported, summarizes how compatible data are with a specified null model; it does not measure the size or importance of an effect. No p-value for the primary endpoint is reported in this record. With the estimate, interval, and any formal comparison absent, a significance claim cannot be made for the primary outcome.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists 105 outcome measures and 14 analyses. With many endpoints, time points, dose groups, and age groups, the chance of finding at least one apparently unusual result can increase if many comparisons are examined. General explanation: multiplicity procedures control or otherwise address the interpretation of repeated statistical tests. They may adjust significance thresholds, organize outcomes into prespecified families, or emphasize estimation rather than isolated p-values. A multiplicity strategy for this study is not reported in the registry record.

The absence of a reported strategy does not establish that no strategy was used in the full protocol or analysis plan. It does mean the registry information does not support claims about family-wise error control, false-discovery control, or a hierarchy among outcomes. The primary endpoint is identified, but no numerical result, confidence interval, or p-value is included in its entry.

For the primary endpoint, the safety population consists of participants who received at least one dose, analyzed according to the treatment received. This defines who was intended for the safety analysis, but the registry does not report how missing diaries, incomplete assessments, withdrawal, or unavailable outcome data were handled. It also does not report the number included in the primary endpoint analysis. Therefore, missing-data effects and differences between the safety population and the analyzed endpoint population cannot be assessed.

The record does not report interim analyses or stopping rules. It also does not report a protocol-based sample-size justification. These omissions should not be filled by inferring that a particular method was used from the number of study phases, enrollment, or the listed outcome count. Interpretation of multiplicity and missing-data handling must remain limited to what the registry record states.

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 1% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: pharyngitis (1.1%), conversion disorder (1.1%), addison's disease (0.7%), sleep apnoea syndrome (0.7%), seizure (0.5%).

The registry’s safety listing separates serious adverse events, other adverse events, and deaths by study group. For each listed group, it gives a number at risk and a number affected for serious and other events. These are descriptive group-level counts, not adjusted comparisons. The groups span different ages, doses, phases, dose schedules, and study settings, so their values should not be treated as directly comparable without accounting for those design differences.

The listing records 0 deaths for each group shown. This is a statement about the recorded groups and does not establish that every possible safety outcome was absent. The registry also names serious-event terms with percentages, including Pharyngitis at 1.1%, Conversion disorder at 1.1%, Addison's disease at 0.7%, Sleep apnoea syndrome at 0.7%, Seizure at 0.5%, and Bronchiolitis at 0.4%. The listed percentages do not by themselves indicate causation, and the relevant denominators and event-level context are not reported alongside those terms in this record.

Serious adverse-event counts should not be confused with the primary endpoint, which concerns local reactions within 7 days after dose 1. The record does not provide the primary endpoint’s event count or estimate. Nor should counts from separate groups be added to create an overall total: group definitions and overlap are not resolved by the registry listing. The appropriate reading is descriptive and cautious, not a treatment-effect conclusion.

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

The record establishes that the study addressed safety, tolerability, and immunogenicity of BNT162b2 in children across multiple ages and dose regimens, with placebo included in some Phase 2/3 groups. It also specifies a primary local-reaction outcome for participants aged ≥5 to <12 years after dose 1, including the observation period, event definition, safety population, and confidence-interval method. These details make the intended measurement understandable.

They do not establish the observed frequency of local reactions. The primary outcome’s percentage and 95% confidence interval are not reported in the registry record. Without those results, readers cannot judge the primary event rate or its precision from this entry. The registry’s adverse-event group counts provide safety information of a different kind and cannot substitute for the missing primary endpoint result.

The study’s non-randomized allocation is also important. A placebo group in a study does not, by itself, make a treatment comparison randomized. Differences between groups may reflect group composition or other factors, and the registry record does not provide an adjustment strategy that would remove this concern. The official title’s description of observer blinding does not align transparently with the recorded masking field of none; the available record does not resolve that inconsistency.

The listed immune-response outcomes indicate that the study considered antibody titers and fold rise at specific time points. Their presence does not establish an immune response result or a clinical effect. Likewise, the existence of multiple age, dose, and outcome groups does not show that every comparison was prespecified or protected against multiplicity.

In short, the registry record supports a description of the study’s questions and measurement methods, but not a conclusion about the primary local-reaction frequency or a causal treatment effect. The record also does not report missing-data procedures, a multiplicity strategy, interim analyses, or a trial-specific sample-size justification. Interpretations should distinguish clearly between reported design details, descriptive safety counts, and results that are not reported in the registry record.

13. Why This Trial Matters Statistically

This trial is statistically notable for the range of design features represented within a single registry record: several pediatric age bands, multiple dose levels, placebo groups, different dose schedules, and Phase 1 and Phase 2/3 components. Such complexity makes careful separation of the study’s questions essential. A short-term local-reaction proportion, an adverse-event count, and a neutralizing-antibody measure answer different questions and should not be treated as interchangeable evidence.

The primary endpoint illustrates why outcome definitions and analysis populations matter. The registry gives a defined observation window, grading criteria, a safety-population definition, and an exact confidence-interval method. These elements support reproducibility in principle. But without the event count, denominator, percentage, or interval, the statistical result itself cannot be evaluated. A well-specified endpoint and a reported estimate are both needed for an interpretable result.

The non-randomized allocation also underscores a basic distinction between describing groups and estimating causal effects. Placebo is listed, and the official title uses placebo-controlled wording, but allocation is recorded as non-randomized. That means group contrasts should not automatically be read as if randomization had balanced participant characteristics. The record’s conflicting masking descriptions add another reason to avoid assuming design protections that are not consistently documented.

Finally, the high number of outcome measures and analyses raises the importance of transparent multiplicity and missing-data reporting. Without those details, readers have limited grounds for assessing how selective findings were handled or how incomplete observations could affect estimates. The statistical importance of this record lies not in an unreported numerical conclusion, but in the clear distinction between detailed measurement plans and the missing information needed to interpret the primary result.

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 central limitation for interpreting the primary outcome is that its numerical result is not reported in the registry record. The entry defines the endpoint and confidence-interval method, but it does not give the observed percentage, interval limits, event count, or analyzed denominator. Consequently, the primary endpoint’s frequency and precision cannot be evaluated.

The trial has a non-randomized allocation field, so listed groups cannot be assumed comparable as randomized arms. This matters across the multiple ages, doses, phases, and schedules in the record. The registry does not report an adjustment approach for group differences. Its official title describes observer blinding for Phase 2/3, whereas the masking field says none; the record does not explain the difference.

The safety listing is organized into groups with differing characteristics, and the record does not establish that the groups are mutually exclusive for purposes of combining counts. Group-specific adverse-event figures should therefore remain group-specific. Serious-event term percentages are listed, but the registry information does not provide the associated denominators or enough context to infer causation.

Details important to interpretation are also not reported: handling of missing outcome data, completeness of diary reporting, the trial’s sample-size justification, interim analyses, and a multiplicity strategy. The registry lists many outcomes and analyses, but does not explain how they were prioritized or jointly interpreted. These omissions limit assessment of statistical uncertainty and selective findings without proving that such procedures were absent from the complete study documentation.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Study to Evaluate the Safety, Tolerability, and Immunogenicity of an RNA Vaccine Candidate Against COVID-19 in Healthy Children — NCT04816643.
• Registry record last updated 2026-05-28; status last verified 2026-05.
• Results first posted 2026-05-28.
• 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 a completed pediatric BNT162b2 study with enrollment of 11837. It lists multiple dose levels, age groups, placebo arms, safety outcomes, and immunogenicity measures. The primary endpoint concerns the percentage of participants aged ≥5 to <12 years in Phase 1 with local reactions within 7 days after dose 1, using a two-sided 95% Clopper and Pearson confidence interval.

The primary endpoint’s numerical result is not reported in the registry record. Allocation is recorded as non-randomized and masking as none, despite the official title’s description of observer blinding in Phase 2/3. Safety data are listed by group, with 0 deaths recorded in each group shown. Missing-data procedures, multiplicity methods, interim analyses, and the study’s sample-size justification are not reported in the registry record.