Immune Response Following Seasonal Influenza Vaccination: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Immune Response Following Seasonal Influenza Vaccination (NCT03163342), a na phase 4 study. The primary outcome is HAI Antibody Immune Response to Matched Influenza Strain H1N1 A/California/04/2009 Strain.

2. Clinical Question

The registry frames the main question around an antibody measurement after vaccination, rather than a comparison of clinical outcomes between treatment groups. It specifies the strain targeted by the primary measure and the time at which that response was to be assessed. The registered endpoint description says the study was intended to evaluate antibody response against the matched strain following seasonal influenza vaccination.

The study also lists secondary outcomes concerning antibody response to divergent influenza strains, cellular immune response, and mucosal influenza antibody response. Those additional measures indicate broader interest in immune response, but the registry record does not report their numerical findings or analyses. It also does not describe an alternative vaccine, placebo, or untreated group for comparison. Accordingly, the primary question can be stated as a measurement of immune response in the vaccinated group; it cannot be reframed as whether vaccination produced a larger response than a control condition.

3. Trial Design

This was a Phase 4, completed, open-label, single-group study sponsored by Altimmune, Inc. The registry record lists enrollment of 20. The study began on 2017-05-08, and primary completion was recorded on 2017-11-21. The listed intervention was a licensed seasonal influenza vaccine, administered intramuscularly. The study summary describes a single administration of the FDA-approved 2016-2017 quadrivalent influenza vaccine to adult healthy male and female volunteers who qualified for the study.

The design is not a randomized comparison. Allocation is recorded as NA, masking is recorded as NONE, and the model is SINGLE GROUP. These descriptors mean that the registry does not identify a randomized assignment process, masking, or a separate control arm. The arm description is Open label, with the licensed vaccine given intramuscularly. With only a vaccinated group listed, the study can describe responses observed after administration, but it cannot estimate a between-group contrast against a concurrent comparator.

The primary outcome is the HAI antibody immune response to matched influenza strain H1N1 A/California/04/2009. It is expressed as a geometric mean titer with a 95% confidence interval, at Day 29 after vaccine. The record lists four outcome measures and zero analyses. It names secondary outcomes for antibody response to divergent influenza strains, cellular immune response, and mucosal influenza antibody response, but does not give their results.

The distinction between a registered endpoint and a reported endpoint result is important. The record identifies what was intended to be measured and when, but it does not supply a numerical primary estimate, confidence interval, or inferential test. Details such as the complete eligibility criteria, the analytic population, and the statistical analysis plan are not reported in the registry record. The enrollment number is not evidence by itself about the precision or adequacy of the primary estimate; that assessment would require the outcome observations and their variability.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Overall Study

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.

6. Primary Endpoint

The registry lists the primary outcome as HAI Antibody Immune Response to Matched Influenza Strain H1N1 A/California/04/2009 Strain, measured over Day 29 after vaccine.

The primary endpoint is the hemagglutination inhibition, or HAI, antibody response to matched influenza strain H1N1 A/California/04/2009, measured at Day 29 after vaccine. The registry expresses the outcome as a geometric mean titer and specifies a 95% confidence interval as its dispersion measure. HAI is an antibody assay measure: it represents the level of antibody activity measured against the named strain, rather than a direct count of influenza infections or a clinical outcome.

A geometric mean is commonly used for titer measurements because such measurements can vary over a wide range and may be asymmetric on their original scale. In general, the geometric mean summarizes multiplicative-scale data by averaging after a logarithmic transformation and then returning to the original scale. This can make it a useful summary for antibody titers, but it does not show the full distribution of individual responses. The registry does not report the underlying participant-level titers or the exact calculation details.

A confidence interval communicates uncertainty around an estimated quantity. In general, a 95% confidence interval describes the range of values compatible with the estimate under the statistical method and its assumptions; it is not a guarantee that an individual participant’s response falls within that range. Here, the record names a 95% interval but gives no interval limits or geometric mean estimate. As a result, the endpoint’s intended meaning is clear, while the magnitude and precision of the observed response cannot be assessed from the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is a continuous antibody-titer summary: a geometric mean HAI titer for a named influenza strain at a specified follow-up time. The registry lists a 95% confidence interval as the measure of dispersion. These choices describe the intended summary and uncertainty measure, but the numerical values and detailed analysis procedure are not reported in the registry record. In particular, the record gives no participant-level values, no transformation details, and no estimation method beyond identifying the geometric mean and confidence interval.

What does a geometric mean summarize?

As a general statistical concept, a geometric mean is suited to measurements that behave multiplicatively or span a broad range. A calculation typically transforms the measurements to a logarithmic scale, averages on that scale, and transforms the result back. On the original scale, the geometric mean is not the same as the arithmetic average. It offers a central summary that can be less influenced by very large values than an arithmetic mean in some distributions, but it still does not describe every participant’s response.

For antibody titers, a group geometric mean cannot reveal whether responses were tightly clustered or widely dispersed. The confidence interval adds information about uncertainty in the group estimate, but it is not an interval containing a stated proportion of individual titers. The registry does not report the interval limits or the underlying distribution, so the degree of variability and the estimate’s precision cannot be evaluated. The record also does not explain how values below an assay’s detection limit, if any, were handled; that detail is not reported in the registry record.

How should a confidence interval be read?

In general, a confidence interval describes uncertainty around an estimate under a specified statistical procedure and its assumptions. A narrower interval indicates greater precision than a wider interval when the intervals concern the same estimand and are constructed comparably. The interval does not measure the probability that the treatment is effective, and it does not establish causation. Its interpretation depends on the sampling and analysis assumptions used to construct it.

The record identifies a 95% confidence interval but supplies neither endpoint. It therefore cannot support a judgment about whether the interval is narrow or wide, nor whether values of substantive interest are compatible with the data. No hypothesis test, p-value, or analysis output is listed. The statistical plan that would clarify the estimation procedure is not reported in the registry record.

What does the design allow the analysis to estimate?

This is a single-group, open-label study. In general, a single-group estimate can describe the measured response among participants assessed after an intervention. It does not yield a randomized treatment contrast because there is no concurrent comparator group listed. A before-and-after contrast could sometimes be analyzed in a single-group study, but the registry does not identify a baseline primary measure or specify such an analysis. It would be inappropriate to assume that one was conducted.

Open-label status means masking is listed as NONE. The record does not say whether laboratory personnel were blinded to samples or whether other procedures reduced measurement bias, so those details are not reported in the registry record. HAI is an assay-based outcome, but the registry does not describe assay conduct, quality controls, or laboratory methods beyond naming the measure.

What do planning calculations mean?

General sample-size planning asks how many observations may be needed to detect a chosen effect under selected assumptions about variability, significance level, allocation, and statistical model. The planning assumptions recorded for this study describe a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation; the effect to detect is specified as a stated fraction of the observed effect. The record also distinguishes total events for time-to-event calculations from participants per arm for other calculations.

Those assumptions describe planning illustrations, not the study design or an observed analysis. In particular, an equal-allocation, two-arm illustration should not be mistaken for the actual single-group design recorded for this study. Sample-size illustrations are hypothetical planning quantities and are never observed power. The numerical planning outputs are not reported in the registry record, so no specific required sample size or planning result can be interpreted. The record also does not report the protocol’s sample-size justification.

More broadly, analysis choices can affect how uncertainty is represented. General methods may account for skew, repeated observations, or over-dispersion when those features are present; over-dispersion means variation is greater than a model expects, and ignoring it can make uncertainty appear too small. The registry does not report a model for the primary endpoint, repeated-measures method, adjustment procedure, or evidence of over-dispersion. None should be inferred from the endpoint label alone.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists four outcome measures, including the primary HAI antibody response and secondary outcomes concerning divergent-strain antibody response, cellular immune response, and mucosal influenza antibody response. It records zero analyses. Numerical results for these outcomes are not reported in the registry record, and no analysis details are given for how the outcomes were handled together.

Multiplicity arises when a study examines several outcomes, time points, groups, or statistical hypotheses. In general, testing multiple hypotheses can increase the chance of at least one apparently unusual result if each is interpreted without accounting for the number of tests. Researchers may address this through a prespecified hierarchy, adjustment, or other analysis strategy. The registry record does not report whether any multiplicity procedure was planned or used. It also does not report an outcome hierarchy beyond identifying the primary endpoint and naming secondary outcomes.

The record does not provide a missing-data summary for the primary or secondary outcomes. It does not state how many participants contributed measurements at Day 29, whether any measurements were unavailable, or how missing values were handled. These details are not reported in the registry record and should not be inferred from the enrollment figure or the safety denominators.

Likewise, the analysis population is not described. The record does not identify whether the primary endpoint was analyzed among all enrolled participants, among participants who received vaccine, or among participants with a valid assay result. It does not report exclusions or protocol deviations. Without those details, the relationship between enrollment and the population underlying any endpoint estimate cannot be assessed.

No interim-analysis plan or stopping rule is reported in the registry record. That absence should not be interpreted as evidence that such procedures were or were not part of a protocol; the relevant details are simply not reported. The available record therefore supports a clear account of the registered outcomes but not a full assessment of missingness, multiplicity, or analysis-population decisions.

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.

The adverse-event record lists a FluZone group with 20 participants at risk for serious adverse events and 0 serious adverse events. It also lists 20 at risk for other adverse events and 0 other adverse events. The death count is 0. These entries describe what the registry reports for the listed group; they do not establish that no adverse event could occur outside the recorded assessment or that risk is absent.

Counts are most informative when interpreted with the event definitions, observation period, and completeness of follow-up. The registry record does not report those details here, nor does it give severity grades or a breakdown of specific event types. It lists no serious adverse-event terms. With no comparator group, the entries also cannot provide a relative safety comparison between vaccine and another condition.

Zero recorded events should not be read as proof of safety or as evidence that the intervention caused no harms. It is a descriptive count for the study group and the registry’s adverse-event reporting. The record does not provide the detail needed to assess how comprehensively events were sought or how long participants were followed for safety reporting.

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

The record establishes that this completed study was designed to measure an antibody response after a single administration of seasonal influenza vaccine in healthy adult volunteers. Its primary endpoint is specifically defined: HAI geometric mean titer against matched H1N1 A/California/04/2009 at Day 29, with a 95% confidence interval named as the dispersion measure. This gives readers a clear description of the intended immunologic question and assessment time.

The record does not report the numerical endpoint result. It therefore does not establish the size of the measured response, its uncertainty, or how participant responses varied. It also does not report p-values or analyses for the primary or secondary outcomes. The absence of a reported result is not evidence of either a high or low response, or of statistical significance or non-significance.

The single-group, open-label structure is important to interpretation. A measured post-vaccination response in this design would be descriptive of the observed participants. Without a concurrent comparator, it would not by itself show how that response differs from what would have occurred under another condition. The record also does not provide a baseline primary value, so a change from baseline cannot be inferred.

The endpoint is an antibody assay measurement, not a direct measure of infection incidence, illness severity, or another clinical outcome. The registry lists secondary immune-response outcomes, but does not report their findings. A result at Day 29 would not by itself describe durability beyond that assessment point; further numerical follow-up information is not reported in the registry record.

The adverse-event entries report zero serious adverse events, zero other adverse events, and zero deaths in the listed group. These entries are not a substitute for detailed safety follow-up or a comparative analysis. Overall, the record describes the study question and design, but it does not provide enough outcome information to quantify the immune response or assess its precision.

13. Why This Trial Matters Statistically

This study illustrates why the endpoint definition and the endpoint result must be kept distinct. A registry can specify the biomarker, strain, summary measure, uncertainty measure, and follow-up time without reporting the estimate itself. Here, the primary outcome is identified as a geometric mean HAI titer with a 95% confidence interval at Day 29, but the estimate and interval are not reported in the registry record. Statistical interpretation cannot proceed from the endpoint label alone.

The design is also central to the scope of inference. A single-group study can describe measurements in participants after an intervention, but it does not supply a randomized between-group contrast. The open-label designation and lack of a listed comparator help define what a result could establish, even if the numerical outcome were available. Clear design descriptions prevent descriptive immune measurements from being mistaken for comparative effects.

The record further demonstrates the importance of reporting analysis details. The number of enrolled participants does not tell readers how many contributed to the endpoint, what variability was observed, how missing measurements were handled, or how the confidence interval was constructed. Those features determine how precisely the result is known and how reproducible its interpretation may be.

Finally, planning illustrations are conceptually different from observed results. Their assumptions can support hypothetical study planning, but cannot replace actual outcome estimates or establish observed power. Keeping these distinctions explicit helps readers understand both the statistical value of a carefully defined immune endpoint and the limits imposed when numerical findings and analysis methods are not reported.

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 main limitation for statistical interpretation is that the registry record does not report the primary endpoint estimate or its confidence limits. Although the endpoint and assessment time are specified, there is no numerical result with which to assess magnitude or precision. The record also lists zero analyses, so it contains no reported inferential analysis for the primary or secondary outcomes.

The single-group design offers no concurrent control comparison. The study is open-label, and masking is recorded as NONE. These design features limit causal interpretation and leave open the possibility of influences unrelated to the intervention. The registry does not report baseline primary measurements or a plan for comparing baseline and follow-up values.

Additional limitations arise from reporting gaps. The analysis population, outcome missingness, participant-level titer distribution, assay details, and exact confidence-interval method are not reported in the registry record. Nor are multiplicity procedures, protocol deviations, or details of any interim analyses reported. The study title refers to durability, but the primary endpoint listed is assessed at Day 29; further outcome timing and numerical follow-up results are not reported.

The adverse-event entries are limited to the listed counts. Definitions, collection methods, follow-up duration, and event-level details are not reported. Consequently, the counts cannot support a detailed comparative safety interpretation. These limitations concern what can be concluded from the registry record; they do not establish that unreported procedures or data were absent from the study itself.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Immune Response Following Seasonal Influenza Vaccination — NCT03163342.
• Registry record last updated 2019-04-26; status last verified 2019-04.
• Results first posted 2019-04-26.
• 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

NCT03163342 is a completed Phase 4, open-label, single-group study sponsored by Altimmune, Inc. The registry lists enrollment of 20 and describes a single intramuscular administration of a licensed seasonal influenza vaccine to healthy adult male and female volunteers. The primary endpoint is HAI geometric mean titer against matched H1N1 A/California/04/2009 at Day 29, with a 95% confidence interval specified.

The registry lists secondary immune-response outcomes but records zero analyses. Numerical outcome results, confidence limits, analysis populations, and missing-data methods are not reported in the registry record. The design has no listed comparator, so it does not support a randomized between-group estimate. The adverse-event entries list zero serious adverse events, zero other adverse events, and zero deaths in the FluZone group.