A COHORT STUDY TO EVALUATE IMMUNOGENICITY FOR CHINESE CHILDREN AT THE TIME OF CLINICAL PNEUMONIA DIAGNOSIS: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for A COHORT STUDY TO EVALUATE IMMUNOGENICITY FOR CHINESE CHILDREN AT THE TIME OF CLINICAL PNEUMONIA DIAGNOSIS (NCT05372575), a non-randomized na study. The primary outcome is Geometric Mean Concentrations (GMCs) of Pneumococcal Immunoglobulin G (IgG) by Cohort.

2. Clinical Question

The study asks what pneumococcal antibody concentrations were measured at the time of clinical pneumonia diagnosis among children aged 5 months to ≤60 months, and how those concentrations differed descriptively between children in the PCV13 and non-PCV13 cohorts. It was a post-launch descriptive immunogenicity study in China, rather than a randomized evaluation of vaccination.

The registry’s primary measure is descriptive: antibody concentrations in serum collected within 24 hours of enrollment. The record does not report the cohort-specific GMC estimates, confidence intervals, or numerical contrasts. Therefore, the clinical question can be described from the stated endpoint, but the magnitude or direction of any cohort difference cannot be established from the registry record.

3. Trial Design

This was a completed, non-randomized, single-group-model cohort study with no masking. The registry lists an enrollment of 300 and identifies Pfizer as the sponsor. The study began on 2019-08-15, its primary completion date was 2021-12-14, and its status is completed. The recorded phase is NA.

The study was described as a post-approval commitment after PCV13 launch in China. Its brief summary says the sponsor was required, based on a recommendation from China Agency, to conduct a descriptive immunogenicity study measuring antibody levels at disease onset. The registered intervention is named “PCV13 PAC study” and categorized as biological. Participants were to be recruited into a PCV13 group or a non-PCV13 group according to whether they had received PCV13 before study start.

Because vaccination status determined cohort membership rather than random allocation, the two cohorts may differ in ways that also relate to antibody concentrations. The registry specifically cautions that the arms are not a like-for-like control comparison. The design can describe concentrations in the enrolled cohorts, but cannot isolate the effect of vaccination from other differences between them.

The primary outcome was measured on Day 1. Approximately 5 mL of blood was collected within 24 hours of enrollment, and serum concentrations of anticapsular IgG were measured by ELISA. The target was each of 13 pneumococcal serotypes. The registry lists four outcome measures and 130 analyses, but does not describe the full analysis structure or provide results for those analyses. A protocol, detailed recruitment flow, and statistical analysis plan 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: No vaccines were administered during the study.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Analysis population for this outcome measure (OM) included all participants who signed the informed consent document, met all inclusion/exclusion criteria, and had at least 1 immunogenicity assay value available for analysis. Overall number of participants analyzed indicates the number of participants in this analysis population. Number Analyzed in each row indicates the number of participants with valid and determinate assay results for the specified serotype.

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: Analysis population for baseline characteristics included all participants who signed the informed consent document.

6. Primary Endpoint

The registry lists the primary outcome as Geometric Mean Concentrations (GMCs) of Pneumococcal Immunoglobulin G (IgG) by Cohort, measured over Day 1.

The primary endpoint is the geometric mean concentration (GMC) of pneumococcal immunoglobulin G (IgG), reported in microgram per milliliter (µg/mL) for each cohort and serotype. Blood was collected within 24 hours of enrollment, and serum anticapsular IgG concentrations were determined by enzyme-linked immunosorbent assay. The endpoint timeframe is Day 1.

The record lists measurements for 13 serotypes: 1, 3, 4, 5, 6A, 6B, 7F, 9V, 14, 18C, 19A, 19F, and 23F. It specifies 95% confidence intervals around the GMCs. The analysis population for this outcome included participants with signed informed consent, who met all inclusion and exclusion criteria, and who had at least 1 immunogenicity assay value available.

In general, a geometric mean is a way to summarize positive measurements that may vary multiplicatively or be unevenly distributed. It is obtained by averaging on a logarithmic scale and transforming back to the original measurement scale. A confidence interval expresses uncertainty around an estimated quantity under the assumptions of the analysis; it is not a range containing every individual participant’s concentration.

These measurements describe antibody concentrations at a single stated time point, not clinical protection or change over time. The registry record does not report the GMC values or confidence intervals, so the endpoint’s numerical findings cannot be interpreted from the record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry describes a cohort-based, descriptive immunogenicity study. Its principal statistical measure is a geometric mean concentration for each cohort and pneumococcal serotype, with a 95% confidence interval. The record does not state the detailed computational procedure, transformations, handling of assay values below quantification limits, or any covariate-adjusted analysis.

Why use a geometric mean?

As a general statistical concept, concentration measurements are often summarized on a logarithmic scale when their distribution is right-skewed or differences are better understood multiplicatively than additively. The geometric mean is the average of the log-transformed observations, transformed back to the measurement scale. It can be more representative than an arithmetic mean when a small number of high values would otherwise pull the average upward. This general rationale does not confirm the precise method used in this study; the registry identifies the endpoint as a geometric mean but does not specify the calculation details.

A GMC is a group summary, not a description of every participant. It does not show the full spread, shape, or overlap of individual concentrations. Two cohorts can have different GMCs while having extensive overlap between individual measurements. Conversely, similar GMCs do not establish that distributions are identical. The registry record does not include individual-level data or a distributional summary that would allow those features to be assessed.

What does the confidence interval express?

In general, a confidence interval communicates uncertainty in an estimate under the statistical model and sampling assumptions used to construct it. A narrower interval indicates greater precision for that estimate under those assumptions; a wider interval indicates less precision. The interval is not a guarantee that a fixed proportion of individual antibody concentrations fall within its bounds. It also does not account automatically for systematic differences between non-randomized cohorts.

The registry specifies 95% confidence intervals for the GMC endpoint, but no limits are reported. Consequently, the precision of any serotype-specific estimate cannot be evaluated. It is also not possible to judge whether apparent differences, if any, are small or large relative to their uncertainty.

Why does cohort assignment matter?

In a randomized study, random allocation is intended to make treatment groups comparable, on average, for measured and unmeasured characteristics. This study was non-randomized: participants were recruited according to prior PCV13 vaccination status. The comparison can therefore reflect both vaccination history and other differences between the cohorts. General examples of possible sources of cohort differences include participant characteristics, healthcare access, or timing and circumstances of vaccination; the registry does not report whether these factors were measured or analyzed.

For that reason, a cohort contrast should be read descriptively. It cannot be interpreted as the causal effect of PCV13. The record explicitly warns that the arms are not a like-for-like control comparison. It does not report an adjusted comparison, a matching strategy, or a prespecified causal estimand.

What is the role of sample-size illustrations?

The record describes planning illustrations based on the observed effect, using a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. The stated effect to detect is a fraction of the observed effect. Such illustrations are hypothetical planning calculations, not observed findings and not evidence that a study had a particular probability of detecting an effect. The registry record does not report the numerical illustration results in the information available for interpretation, nor does it report the study’s own sample-size justification. The illustrations therefore cannot be used to infer the original design rationale or the precision of the immunogenicity estimates.

General sample-size calculations depend on assumptions about the target effect, variability, analysis method, and allocation. If those assumptions differ from the study’s realized data or intended estimand, the resulting planning figures may not describe actual precision. They are distinct from a confidence interval calculated from observed data.

What remains unspecified?

The record lists 130 analyses but does not explain which tests, models, contrasts, or endpoints those analyses cover. It does not state whether the GMCs were compared formally between cohorts, whether any hypothesis tests were performed, or which serotypes or analyses were prespecified. It also does not describe missing-value procedures, assay quality rules, or adjustments for multiple comparisons. Without those details and without numerical endpoint results, the analysis cannot be independently reconstructed or evaluated beyond the stated measure and design.

10. Multiplicity, Missing Data and Analysis Populations

The primary outcome spans 13 pneumococcal serotypes, and the registry lists four outcome measures and 130 analyses. That creates a context in which multiple estimates or statistical tests may have been generated. However, the record does not describe the 130 analyses, identify which were confirmatory or exploratory, or report a multiplicity strategy. It is therefore not possible to determine whether any family of comparisons was defined or whether confidence intervals or tests were adjusted for multiple comparisons.

In general, when many hypotheses are tested, the chance of at least one apparently unusual result can increase if each test is interpreted without accounting for the number of tests. Whether that issue is relevant to a particular result depends on the analysis plan and the intended interpretation. The registry does not report enough detail to characterize that risk for this study. The absence of a stated adjustment should not be interpreted as proof that no adjustment was used; the approach is not reported in the registry record.

The primary outcome’s analysis population required informed consent, eligibility, and at least 1 immunogenicity assay value. This definition does not establish that all such participants had usable values for every serotype. The number included in each cohort-specific, serotype-specific estimate and the extent or pattern of missing assay values are not reported in the registry record. The record also does not state how missing measurements, invalid assays, or values outside assay limits were handled.

Because enrollment is listed as 300 while the primary outcome description does not provide analysis denominators, enrollment cannot be treated as the number contributing to every GMC. The record’s population wording indicates eligibility for analysis, not necessarily complete data for all endpoint components. No participant flow or comparison of included and excluded participants is reported. These omissions limit assessment of representativeness and potential missing-data bias.

The registry does not report a detailed statistical analysis plan, prespecified hierarchy among outcomes, or interim-analysis plan. Those details should not be inferred from the number of listed analyses or the stated confidence level.

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 5% reporting threshold.

The registry lists serious adverse event counts by cohort. For the 13vPnC Cohort, 101 participants were at risk, 0 were affected by a serious adverse event, 101 were at risk for other adverse events, and 0 were affected by other adverse events; deaths are listed as 0. For the Non-13vPnC Cohort, the corresponding figures are 199 at risk, 0 affected by serious adverse events, 199 at risk for other adverse events, 0 affected by other adverse events, and 0 deaths.

These are registry counts, not estimates of comparative risk. A recorded count of 0 means no event was entered for that category in the listed cohort; it does not prove that an event is impossible or that the cohorts are equivalent. The non-randomized design also means the groups should not be treated as directly comparable controls. The registry lists no top serious adverse event terms. The record does not provide further event definitions, follow-up duration for safety, or detailed safety-analysis methods, so those aspects cannot be assessed from the listed counts.

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

The study’s documented purpose was to describe pneumococcal antibody concentrations at disease onset among children with clinical pneumonia in China, distinguishing cohorts by prior PCV13 vaccination. It establishes the intended endpoint, the Day 1 sampling timeframe, the assay, the serotypes assessed, and the broad cohort design. The registry also records 0 serious adverse events, 0 other adverse events, and 0 deaths in each listed cohort, with the respective at-risk counts of 101 and 199.

The registry record does not report the primary GMC estimates or 95% confidence intervals. As a result, it is not possible to state what antibody concentrations were observed, whether they differed between cohorts, or how precise the estimates were. No conclusion about the direction or magnitude of an immunogenicity contrast can be supported by the available numerical outcome information.

Even with cohort-specific GMC results, the observational comparison would remain descriptive. Since vaccination was not randomized, differences could reflect factors other than vaccination history. The study’s registered design does not support interpreting an unadjusted cohort contrast as the causal effect of PCV13. The record does not report a causal analysis or adjustment strategy.

Antibody concentration is a laboratory measure, not itself a clinical outcome. The registry does not state a protective threshold or show that a particular concentration predicts an individual child’s outcome. A measurement at enrollment also does not describe changes over time. The reported endpoint should therefore be understood as a snapshot of serum IgG concentrations, not as a direct assessment of clinical protection, pneumonia severity, or subsequent outcomes.

In general, a confidence interval can show uncertainty around an estimate, while design features determine how strongly the estimate supports a causal interpretation. Both matter: statistical precision cannot remove confounding from non-randomized cohort membership. Here, neither the numerical endpoint estimates nor the details needed to assess adjusted comparisons are reported in the registry record.

13. Why This Trial Matters Statistically

This study is statistically informative as an example of a descriptive immunogenicity question embedded in a non-randomized cohort design. The primary endpoint is defined at the level of serotype-specific GMCs, with 95% confidence intervals, and uses serum obtained within 24 hours of enrollment. This makes clear what biological measurement the study intended to characterize and at what time point.

The design distinction matters. Cohorts based on prior vaccination can describe antibody concentrations among the enrolled participants, but their contrast does not have the protection against confounding that random assignment is intended to provide. A statistical difference, if reported, would not by itself identify vaccination as its cause. The registry itself warns that the two arms are not a like-for-like control comparison.

The record also illustrates why endpoint definitions and analysis populations need to be read together. The analysis population requires at least 1 immunogenicity assay value, while the outcome includes measurements for 13 serotypes. Without serotype-specific denominators and missing-data information, the extent to which all enrolled participants contribute to each summary is unclear.

Finally, the record shows the limits of interpreting a registry entry without numerical endpoint results. It provides a study objective, endpoint definition, timing, and cohort framework, but does not report the GMCs or their intervals. Statistical interpretation depends not only on the stated method but also on estimates, uncertainty, and the population analyzed. The posted safety counts do not fill that gap or answer the immunogenicity question.

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 principal limitation for interpretation is that the registry record does not report the primary outcome estimates or their 95% confidence intervals. The direction, magnitude, and precision of the serotype-specific GMCs therefore cannot be evaluated. Although the record lists 130 analyses, it does not explain their contents or identify the analysis corresponding to any reported result.

The cohort comparison is non-randomized and explicitly not a like-for-like control comparison. Prior vaccination determines cohort membership, so measured or unmeasured differences between cohorts may contribute to any observed contrast. The record does not report adjustment methods or participant characteristics that would help assess this issue.

The outcome population is described as participants meeting eligibility requirements and having at least 1 assay value available. The registry does not report cohort and serotype-specific denominators, participant flow, missingness, assay exclusions, or handling of values outside measurement limits. It is not possible to determine from enrollment alone how many participants contributed to each GMC.

The primary endpoint is a single-timepoint antibody measurement at Day 1. The record does not report a clinical correlate or threshold for interpreting the measured concentrations, nor does the endpoint directly measure clinical outcomes. Follow-up details relevant to interpreting the safety counts are also not reported in the registry record.

The registry does not report the detailed statistical analysis plan, sample-size justification, prespecified status of analyses, or multiplicity procedures. Its planning illustrations are not the study’s own design justification. These gaps limit evaluation of whether the analyses followed prespecified methods and how uncertainty or multiple comparisons were handled.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: A COHORT STUDY TO EVALUATE IMMUNOGENICITY FOR CHINESE CHILDREN AT THE TIME OF CLINICAL PNEUMONIA DIAGNOSIS — NCT05372575.
• Registry record last updated 2023-10-03; status last verified 2022-12.
• Results first posted 2023-10-03.
• 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

NCT05372575 is a completed, non-randomized cohort study sponsored by Pfizer, with an enrollment of 300. It was designed to describe pneumococcal IgG concentrations among children aged 5 months to ≤60 months at clinical pneumonia diagnosis in China, comparing cohorts according to prior PCV13 vaccination. The study began on 2019-08-15, reached primary completion on 2021-12-14, and is listed as completed.

The primary measure is Day 1 serotype-specific GMC, with 95% confidence intervals, based on serum collected within 24 hours of enrollment and measured by ELISA. The registry lists 13 pneumococcal serotypes. Cohort membership was not randomized, and the registry cautions that the arms are not a like-for-like control comparison.

The record lists 0 serious adverse events, 0 other adverse events, and 0 deaths in each cohort, with 101 and 199 participants at risk, respectively. Primary GMC values, confidence intervals, analysis denominators by serotype, and detailed statistical methods are not reported in the registry record.