Randomized Study of Immune Response to Licensed Influenza Vaccines in Children and Adolescents: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Randomized Study of Immune Response to Licensed Influenza Vaccines in Children and Adolescents (NCT02250274), a randomized phase 4 study. The primary outcome is Hemagglutination Inhibition (HI) Titer Response to Vaccine and Circulating Strains of Influenza.

2. Clinical Question

The study was designed to assess serologic and cell-mediated immune responses to licensed live attenuated influenza vaccine (LAIV) and inactivated influenza vaccine (IIV) in children 5-17 years old. It also aimed to examine how prior influenza infection and prior-season vaccination relate to those responses. Children were to be followed during the influenza season for laboratory-confirmed influenza illness.

The clinical question therefore has two parts: the immune response after vaccination, and whether the response differs across the two vaccine groups in the study population. The registry also lists PCR-confirmed influenza illness, antibody-dependent cellular cytotoxicity titers, and the ratio between immunoglobulin A and immunoglobulin G among the secondary outcomes. It does not report outcome results for these measures.

3. Trial Design

This was a completed, randomized, parallel-group Phase 4 study sponsored by Marshfield Clinic Research Foundation. The registry lists enrollment of 131. The study began in 2014-09, had primary completion in 2014-12, and is recorded as completed. Masking is listed as none, so the registry describes the study as unmasked.

Participants were assigned to receive LAIV or IIV. The arm descriptions indicate that the groups were not drawn from identical age ranges: the LAIV group included 5-8 year olds and approximately half of the 9-17 year olds, while the IIV group included only 9-17 year olds unless LAIV shortages occurred. The descriptions also refer to prior histories of vaccine failure, vaccination without infection, and neither vaccination nor infection in the prior season. The registry notes that peripheral blood mononuclear cells were available for some participants with prior infection, with age eligibility differing between the groups.

Random assignment can help balance participant characteristics across groups, but the registry does not report the allocation procedure or how the age and prior-history categories were handled in the analysis. It also does not report the numbers enrolled in each randomized group as an enrollment summary. The safety listings do give group-specific denominators, which are described separately in the safety interpretation.

The stated study purpose included measuring serologic and cell-mediated responses and following children during the influenza season to identify laboratory-confirmed influenza. The primary endpoint is specified as change in HI titer from baseline to 28 days. The registry does not report the full visit schedule, a detailed protocol, or the statistical analysis plan. It therefore does not establish from the posted information how all outcomes, time points, or participant subgroups were to be compared.

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

Reasons for not completing this period:

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 Hemagglutination Inhibition (HI) Titer Response to Vaccine and Circulating Strains of Influenza, measured over Change from Baseline to 28 days.

The primary endpoint is hemagglutination inhibition (HI) titer response to vaccine and circulating influenza strains, expressed as geometric mean titers with 95% confidence intervals. The registry defines the timeframe as change from baseline to 28 days. HI testing measures antibodies that can inhibit influenza virus hemagglutination in a laboratory assay; it is used as a serologic measure of the antibody response to influenza antigens.

Geometric means are often used for antibody titers because titer measurements can be skewed, with some values much larger than others. A geometric mean summarizes values on a multiplicative scale rather than taking an ordinary arithmetic average. This is a general statistical explanation; the registry does not report the distribution of titers or the transformation used in its analysis.

A 95% confidence interval expresses uncertainty around an estimated quantity under the assumptions of the method used. A narrower interval indicates greater precision than a wider interval, but the interval alone does not show whether a difference between groups is clinically important. For a comparison, the estimate and its uncertainty need to be interpreted together, with attention to the precise contrast being estimated.

The registry record gives the endpoint definition but does not report geometric mean titer estimates, confidence interval limits, or a treatment-group contrast. It is therefore possible to describe what the primary endpoint was intended to measure, but not the size or precision of the observed immune response from the registry information.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry identifies a randomized, parallel-group design without masking. In a randomized study, assignment by chance is intended to reduce systematic differences between groups at baseline. Randomization does not guarantee that every measured or unmeasured characteristic will be balanced, especially in a particular sample. The registry does not report the sequence-generation method, concealment of assignment, or procedures used to implement randomization, so those features cannot be assessed from the record.

What does the primary measure summarize?

HI titers are the laboratory measure specified for the primary endpoint. The registry describes the summary as a geometric mean and the uncertainty as a 95% confidence interval. A geometric mean is appropriate in some settings where measurements vary multiplicatively or are strongly skewed. In general, it is obtained by working on a logarithmic scale, averaging there, and transforming back. This is a general explanation, not a claim about the exact analysis conducted in this study; the registry does not report its calculation details.

The stated endpoint is change from baseline to 28 days. A change endpoint uses each participant’s baseline measurement as a reference for later measurement. Statistical approaches can summarize within-participant change, compare changes between groups, or model repeated measurements. Those approaches estimate different quantities and rely on different assumptions. The registry does not report which approach was used, whether baseline values were included as covariates, or how measurements from different strains were handled.

How should a confidence interval be read?

In general, a confidence interval gives a range of values compatible with the observed estimate under the model and sampling assumptions. It communicates uncertainty more directly than an estimate alone. It does not mean that every value inside the interval is equally likely, and it does not by itself establish that a result is clinically meaningful. To interpret a group comparison, a reader would need to know the contrast, the estimated difference or ratio, its confidence interval, and the analysis model. The registry lists the confidence-interval type for the primary endpoint but does not report the intervals or the group contrast.

Repeated immune measurements can be correlated within a participant, and responses to different influenza strains may also be related. General methods for such data can account for within-person dependence or define a separate endpoint for each strain. The registry does not specify which strains were analyzed, how multiple measurements were combined, or whether a repeated-measures model was used. No particular model can therefore be attributed to this study.

What is the role of the planning illustrations?

Sample-size planning asks how many participants would be needed under stated assumptions to detect a chosen effect with a chosen statistical operating characteristic. The planning illustrations associated with this analysis use a two-sided significance level of 0.05, equal allocation, and a normal approximation, with the target effect expressed as a fraction of the observed effect. These are planning assumptions, not evidence that the trial was designed using them. The registry does not report the trial’s sample-size justification or its planned effect size, and the illustrations must not be interpreted as observed power.

The distinction between an observed estimate and an assumed effect is important. A planning illustration can show how requirements would vary under its assumptions, but it does not demonstrate that the study actually had a particular probability of detecting an effect. Nor does it show that a nonsignificant result would establish equivalence or absence of a meaningful difference. No such conclusion can be drawn without the actual result and a suitable analysis.

Why do analysis choices matter?

Age and prior influenza history may relate to immune response. The arm descriptions show different age eligibility and identify prior-season categories, but the registry does not report whether these factors were adjusted for or used to define subgroups. If baseline characteristics differ between groups, an unadjusted comparison and an adjusted comparison can yield different estimates. The relevant analysis depends on the study question and the prespecified plan, neither of which is fully reported.

Multiple outcomes or comparisons raise a general multiplicity issue: the more statistical questions examined, the greater the chance that at least one result appears notable by chance if no adjustment or interpretive framework is used. This study lists several outcomes, but the registry does not report the number of statistical tests, a testing hierarchy, or a multiplicity strategy. It is therefore not possible to assess how multiplicity was handled.

Missing measurements can also affect estimates. General methods include analyzing participants with observed measurements, imputing missing values under specified assumptions, or using models that accommodate incomplete repeated data. Each method has assumptions, and the method should be described alongside the analysis population and missing-data pattern. The registry does not report missing primary endpoint data, exclusions, imputation, or the analysis population. Accordingly, no specific missing-data method can be inferred.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists four outcome measures, including the primary HI titer response and secondary measures related to PCR-confirmed influenza illness, antibody-dependent cellular cytotoxicity titers, and the immunoglobulin A to immunoglobulin G ratio. It records zero analyses. The record does not describe a statistical testing hierarchy, a primary comparison for each secondary outcome, or a method for controlling the chance of false-positive findings across multiple outcomes or strains. Whether or how multiplicity was addressed is not reported in the registry record.

Missing-data handling is also not described. The registry does not report how many participants had baseline and 28-day HI measurements, whether any participants were excluded from endpoint analyses, or whether incomplete measurements were imputed. It does not identify an analysis population such as all randomized participants or participants with available measurements. These details are necessary for understanding which participants contributed to an estimate and how incomplete follow-up may affect it.

The study purpose notes follow-up during the influenza season, but the registry does not report follow-up completeness or a statistical method for handling participants who did not complete follow-up. The availability of peripheral blood mononuclear cells is described for particular prior-infection and age groups, but no analysis population or missing-sample strategy is specified. These reporting gaps limit assessment of selection and missing-data bias; they do not establish that such bias occurred.

11. Safety Results

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

Other (non-serious) adverse events

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

The registry lists serious adverse events by vaccine group. For LAIV 2014-15, the serious adverse-event count is 0 among 85 participants at risk. For IIV 2014-15, the count is 0 among 46 participants at risk. The other adverse-event category also lists 0 among 85 for LAIV and 0 among 46 for IIV. These are the counts and denominators recorded in the registry.

A zero count means that no events were recorded in that category for the stated group denominator in this registry listing. It does not establish that the event risk is zero, nor does it provide a precise estimate of risk in other populations or settings. Interpretation also depends on the event definitions, collection procedures, observation period, and completeness of reporting. Those details are not reported in the registry record.

The deaths fields are not reported in the registry record. They should not be interpreted as a confirmed count of zero. The safety figures are limited to the listed categories and do not describe all possible adverse events or provide a comparison adjusted for participant characteristics.

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

The registry record establishes that a randomized, parallel-group study was conducted to assess immune responses to LAIV and IIV in children and adolescents. It specifies HI titer change from baseline to 28 days as the primary endpoint and lists geometric mean titers with 95% confidence intervals as the summary. It also identifies secondary outcomes and posts adverse-event counts by group.

Those details do not establish the size or direction of the immune response. The primary estimates and confidence intervals are not reported in the registry information available for interpretation, and the record lists zero analyses. There is no posted statistical comparison from which to judge whether the groups differed, how precise an estimate was, or whether a difference was clinically important. The absence of a reported analysis is not evidence that the groups had identical responses.

The same caution applies to secondary outcomes. The study purpose describes laboratory-confirmed influenza follow-up, and the record lists several immune measures, but no corresponding results are reported. An endpoint being named does not mean that its outcome was favorable, unfavorable, or even fully observed.

The recorded adverse-event counts are 0 in both listed categories for each vaccine group. Those entries describe the registry counts, not a guarantee of safety or a general estimate of risk. The record does not report deaths, event definitions, or the details needed to evaluate the completeness of safety monitoring.

In short, the posted information supports a description of the study question, design, endpoint definition, and selected safety counts. It does not support a conclusion about comparative vaccine performance, immune-response magnitude, or the absence of risk. Such conclusions would require outcome estimates, uncertainty intervals, and analysis details that are not reported in the registry record.

13. Why This Trial Matters Statistically

This study illustrates why an endpoint definition and an endpoint result are different kinds of information. The registry specifies a laboratory measure, a summary scale, an uncertainty measure, and a follow-up interval. Those details make the scientific question identifiable, but they do not answer it without estimates and an analysis. Readers need the result and its precision to assess the evidence rather than relying on the study objective or outcome label.

The design also highlights the importance of examining who was eligible for each group. The LAIV and IIV descriptions differ by age range, and the record notes prior infection and vaccination histories. These features may matter when interpreting immune-response comparisons. Randomization is a strength of the design in principle, but the registry does not report how these features were represented in the analysis. A clear account of the analyzed population and adjustment strategy would help readers understand the comparison.

The posted safety counts offer another statistical lesson: zero recorded events are not equivalent to proof of zero risk. Counts must be read alongside denominators, event definitions, and the observation period. Here, denominators are listed, but additional safety-reporting details are not reported in the registry record.

Finally, planning calculations should not be confused with observed evidence. Sample-size illustrations depend on assumptions about effect size, allocation, significance level, and the approximation used. They can inform planning under those assumptions, but they are not a substitute for the trial’s own design justification or for the observed outcome analysis. Keeping planning, estimation, and inference distinct is essential when a registry reports a study design without its outcome estimates.

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 of the registry information for interpreting this trial is that it does not report the primary HI titer estimates or confidence intervals, despite naming the endpoint and its timeframe. It also lists zero analyses, so no reported comparison can be assessed. The record does not provide numerical results for the secondary outcomes.

The arm descriptions identify different age eligibility: the LAIV group included 5-8 year olds and approximately half of those 9-17 years old, while the IIV group included only those 9-17 years old unless LAIV shortages occurred. The registry does not report the actual age distribution by group or how age was addressed analytically. Prior vaccination and infection histories are described, but their distribution and role in the analysis are not reported.

Other study details needed for statistical appraisal are also absent. The registry does not report the randomization procedure, the analysis population, missing-data methods, endpoint-specific sample sizes, or the model used for the primary analysis. It does not report how the multiple outcomes, strains, or time points were handled statistically. These omissions prevent a detailed assessment of precision, risk of bias, and the robustness of any comparison.

The safety entries list zero events in the specified categories, but the deaths fields are not reported. Event definitions, collection methods, and follow-up completeness are also not reported in the registry record. These limitations describe gaps in the posted information and should not be treated as evidence that the study lacked procedures or that unreported outcomes did not occur.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Randomized Study of Immune Response to Licensed Influenza Vaccines in Children and Adolescents — NCT02250274.
• Registry record last updated 2018-04-26; status last verified 2018-03.
• Results first posted 2016-02-26.
• 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

This completed Phase 4 randomized, unmasked, parallel-group study compared licensed LAIV and IIV in children and adolescents. The registry lists enrollment of 131 and identifies Marshfield Clinic Research Foundation as the sponsor. The study began in 2014-09 and reached primary completion in 2014-12.

The primary endpoint was HI titer response to vaccine and circulating strains, measured as geometric mean titers with 95% confidence intervals for change from baseline to 28 days. The record lists four outcome measures and zero analyses, and does not report primary or secondary outcome estimates. Safety listings record 0 serious adverse events and 0 other adverse events in each vaccine group; deaths are not reported in the registry record.