Randomized Trial of High Dose Influenza Vaccine in Long Term Care Setting: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Randomized Trial of High Dose Influenza Vaccine in Long Term Care Setting (NCT01654224), a randomized phase 4 study. The primary outcome is Non-inferiority of High-dose Inactivated Influenza Vaccine(HDIV) Versus Standard Dose Inactivated Influenza Vaccine(SDIV) Among Residents of Long Term Care(LTC) Settings.

2. Clinical Question

The study asks a comparative immunogenicity question: how the antibody-titer responses associated with the two vaccine doses compare among long-term care residents. Its stated primary objective is non-inferiority, rather than a test designed only to determine whether the high-dose group has a larger response. The registry record describes comparing baseline and post-vaccination HAI and MN titers, with the primary timeframe given as 30 days.

The study summary frames the broader question as whether the high-dose vaccine provides protection that is the same or better than the regular-dose vaccine. However, the primary outcome described in the record is based on titers. It does not describe a primary comparison of influenza illness, hospitalization, or another clinical event. The record says both vaccines are approved for use in older adults; it does not provide further details about participants’ ages or health status.

A non-inferiority question requires a prespecified margin: the largest difference that would still be considered compatible with non-inferiority. That margin is not reported in the registry record. Nor does the record state the numerical titer estimates or their confidence intervals. As a result, the research question can be described, but the posted information does not establish whether the study met its non-inferiority objective.

3. Trial Design

The registry identifies this as a completed Phase 4, randomized, single-masked, parallel-group trial. The listed enrollment is 205. The study began in 2011-11, and its primary completion date is 2014-06. The sponsor is the University of Pittsburgh. The record names influenza as the condition under study and describes the setting as long-term care.

Participants were assigned to one of two vaccine groups: High Dose Inactivated Influenza Vaccine or Standard Dose Inactivated Influenza Vaccine. The high-dose description specifies 0.5 ml with a total of 180mcg of hemagglutinin, 60 mcg for each strain. The standard-dose description specifies 0.5 ml with a total of 45 mcg, 15 mcg for each strain. The registry does not report the randomization method, allocation ratio, or whether assignment was stratified by any participant or facility characteristics.

The record calls the study single-masked but does not identify who was masked. It does not report the procedures used to maintain masking or whether masking continued through laboratory measurement and analysis. The parallel-group description means the two vaccine groups are treated as separate arms in the trial record; details about follow-up, adherence, or changes in assigned treatment are not reported there.

The primary outcome is described as a comparison of baseline and one-month post-vaccination HAI and MN titers. A secondary outcome concerns non-inferiority and persistence of immunoprotection at 6 months. The registry lists three outcome measures and 18 analyses, but does not give enough detail to map each analysis to a specific endpoint, time point, or analysis population. The record also does not state a statistical analysis plan or explain how the target enrollment was chosen.

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: A total of 205 participants from 15 community-based LTCFs who met all inclusion and none of the exclusion criteria were enrolled.

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 Non-inferiority of High-dose Inactivated Influenza Vaccine(HDIV) Versus Standard Dose Inactivated Influenza Vaccine(SDIV) Among Residents of Long Term Care(LTC) Settings, measured over 30 days.

The primary endpoint concerns HAI and MN titers, which are laboratory measurements used to describe antibody responses to influenza vaccination. The registry specifies geometric mean titers and 95% confidence intervals, with measurements compared from baseline to one month after vaccination; the timeframe is also given as 30 days. These measures describe an immune response, rather than directly counting influenza infections or other clinical events.

Geometric means are often used for titer data because measurements can be spread across a wide range and may be skewed. In general, a geometric mean summarizes values on a multiplicative scale and can be more representative than an arithmetic mean when relative changes are of interest. The registry record does not report the transformation or calculation details used for these outcomes, so those details cannot be confirmed for this trial.

A confidence interval expresses the uncertainty around an estimated quantity under the analysis assumptions. For a non-inferiority assessment, the estimated group contrast and its interval must be interpreted relative to a prespecified margin. The record gives the interval type but does not report the margin or the numerical titer results. Therefore, the endpoint definition explains what was intended to be measured, but the registry information does not permit an assessment of the primary non-inferiority finding.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The central statistical feature is the non-inferiority objective. In general, a non-inferiority study asks whether the intervention’s performance is not worse than the comparator by more than a prespecified acceptable margin. The margin defines what difference would count as too large to accept. It needs to be selected before examining the study results and justified in relation to the clinical and scientific context. The non-inferiority margin for this trial is not reported in the registry record.

How is non-inferiority assessed?

In general, the assessment uses an estimate of the difference between groups and a confidence interval around that estimate. The interval is compared with the non-inferiority margin. The direction of the contrast and the placement of the interval relative to the margin are essential; an estimate that appears close between groups is not, by itself, enough to establish non-inferiority. A non-significant test of difference is also not equivalent to evidence of non-inferiority. The registry identifies 95% confidence intervals but does not report the group contrast, interval limits, margin, or testing details.

Confidence intervals communicate both the estimated value and its precision under the statistical model. A narrower interval indicates greater precision than a wider interval, but whether an interval supports a specific conclusion depends on the relevant decision threshold. Here, the record names the confidence interval level but contains no numerical primary interval to evaluate. No conclusion about precision or the non-inferiority boundary can be drawn from the interval label alone.

Why report geometric mean titers?

HAI and MN titers are laboratory measurements of antibody response. In general, titer values can have a skewed distribution, so geometric means are commonly used to summarize them on a multiplicative scale. A geometric mean reflects the central tendency after values are represented on a logarithmic scale and transformed back. This can make relative differences more interpretable when values vary substantially. The registry identifies the parameter as a geometric mean, but does not report the exact calculation, transformation, handling of values below assay limits, or model used.

The outcome description refers to comparing baseline with one month after vaccination. Such a comparison may be expressed in different ways, including post-vaccination levels, change from baseline, or a ratio of geometric means. These approaches answer related but not identical questions. The record does not specify which contrast generated each analysis or how baseline values were incorporated. It would be inappropriate to assume a particular adjustment or change-score method.

What do HAI and MN measure?

In general, HAI and MN are distinct laboratory assays used to assess aspects of antibody response. Reporting both provides more than one immunological measure, but it also creates multiple quantities that may require clear prespecification and interpretation. The registry describes both assays in the primary objective, but does not identify how many strains or assay-specific comparisons were planned, which were primary within the endpoint, or how results across assays were combined for a decision.

The primary timeframe is given as 30 days, and the endpoint description calls this one month after vaccination. The secondary outcome concerns persistence at 6 months. Measurements at different time points address different questions: an early post-vaccination response and persistence over follow-up should not be treated as interchangeable. The registry does not provide numerical results for either period or describe how repeated measurements were modeled.

What can the planning illustrations tell readers?

The planning illustrations are described as calculations based on the observed effect, using a two-sided significance level of 0.05, equal allocation between arms, and a normal approximation. They are not the trial’s own design justification. In general, an illustration based on an observed effect asks what sample size might be required under stated assumptions to detect that effect. It is sensitive to the effect chosen and the assumptions used, and it does not show the probability that this completed trial would have produced a statistically significant result. It is not observed power.

For these illustrations, the effect to detect is defined as a stated fraction of the observed effect. The record’s general description distinguishes participant counts per arm from total event counts for time-to-event calculations. These planning conventions should not be mistaken for the original protocol. The registry does not report the original sample-size calculation or justification, and the planning assumptions do not establish what assumptions investigators used when designing the trial.

Over-dispersion is a general statistical concern when observed variability is greater than a model expects. If a model understates variability, confidence intervals can be too narrow and uncertainty can be understated. Whether over-dispersion is relevant depends on the outcome distribution and model. The registry record does not name the primary analysis model or provide information that would show whether over-dispersion was assessed, so no trial-specific claim about it is warranted.

What analysis details remain unknown?

The record does not report the non-inferiority margin, exact statistical tests, model covariates, transformations, missing-measurement procedures, or analysis populations. It also does not describe sensitivity analyses or the treatment of protocol deviations. These details are important because non-inferiority conclusions can depend on analytic choices and on how participants with incomplete follow-up are handled. The presence of 18 listed analyses does not by itself reveal which analysis was primary or whether results were adjusted for multiple testing.

10. Multiplicity, Missing Data and Analysis Populations

The registry record lists three outcome measures and 18 analyses. It does not provide a detailed map of the analyses to outcomes, assay types, time points, or contrasts. Those counts alone do not establish how many independent hypotheses were tested or which results were considered confirmatory.

Multiplicity arises when several statistical tests or comparisons are considered together. In general, the more opportunities there are to identify a result, the more important it is to prespecify the primary comparison and decide whether adjustment or a hierarchical testing strategy is needed. The record does not report a multiplicity plan, adjustment method, testing hierarchy, or distinction between confirmatory and exploratory analyses. It is therefore not possible to determine from the registry whether or how multiplicity was addressed.

The primary objective includes both HAI and MN titers and compares baseline with a post-vaccination measurement. The record also identifies persistence at 6 months as a secondary outcome. It does not explain how conclusions across these measures and time points were to be combined. No single numerical primary comparison is reported, and the record states that the primary outcome has several categories or time points and is not reduced to one comparison.

Missing-data methods and analysis populations are not reported in the registry record. The record does not say how many participants contributed to each titer analysis, how missing measurements were handled, or whether the primary analysis used an intention-to-treat, per-protocol, or other population. These omissions are particularly relevant to non-inferiority interpretation: in general, missing data and analysis-population choices can affect the estimated group difference and the strength of a conclusion. No trial-specific sensitivity analysis can be assessed from the information reported.

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 adverse-event information lists two groups, HD IIV and SD IIV. For HD IIV, 89 were at risk for serious adverse events and 0 were recorded as affected; 89 were at risk for other adverse events and 0 were recorded as affected. For SD IIV, 98 were at risk for serious adverse events and 0 were recorded as affected; 98 were at risk for other adverse events and 0 were recorded as affected.

These are the registry’s listed counts and denominators for the adverse-event categories. They should be read as the event information reported in the record, not as a complete account of every aspect of safety monitoring. The record does not provide event descriptions, a detailed observation period, definitions, collection procedures, or a narrative about safety events. Deaths are not reported in the registry record.

A zero count in these entries does not establish that no adverse events of any kind occurred, and it does not determine the safety profile beyond the categories and information recorded. The adverse-event denominators should not be assumed to represent the primary titer analysis populations; the registry does not explain their relationship. These figures also do not address comparative efficacy, since the primary outcome concerns antibody titers rather than adverse events.

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

The registry record makes clear what the trial set out to compare: high-dose and standard-dose inactivated influenza vaccines in residents of long-term care settings, with a primary non-inferiority question based on HAI and MN titers. It also documents the vaccine formulations and the intended early measurement period. This is useful for understanding the study question and its immunogenicity focus.

It does not, however, report the numerical primary results needed to judge the outcome. The registry gives no titer estimates, group contrast, confidence interval limits, or non-inferiority margin. Consequently, the information does not show whether non-inferiority was demonstrated, how precise the estimate was, or how the observed result compared with the study’s decision threshold.

The study summary discusses protection, but the described primary outcome is antibody titers. A titer comparison is not the same as a direct comparison of influenza cases or other clinical events. The registry record does not report such a clinical endpoint result. Therefore, the posted information cannot establish a difference in clinical protection between the two vaccine groups.

Nor does the absence of a reported numerical primary result mean that the trial found no difference. It means that the registry information available for interpretation does not provide the estimates required to make that judgment. The stated objective, completed status, and enrollment do not substitute for the outcome data and analysis details.

The adverse-event entries report zero affected in the listed serious and other adverse-event categories for both groups, with their respective at-risk denominators. These limited entries should not be expanded into a general claim about all possible harms or all safety follow-up. The registry also identifies a secondary persistence outcome at 6 months, but does not report its numerical results.

Overall, the record supports a description of the trial design and intended comparisons. It does not support a conclusion about non-inferiority, superiority, clinical protection, or the precision of the primary result. Those judgments require numerical outcomes, the margin, and fuller analysis information that are not reported in the registry record.

13. Why This Trial Matters Statistically

This trial is statistically interesting because its stated primary objective is non-inferiority. That design asks a different question from a conventional test for any group difference. It depends on a prespecified margin and on interpreting the estimate and its uncertainty relative to that margin. Without the margin and numerical confidence interval, readers cannot evaluate the central statistical claim, even though the registry describes the endpoint and confidence interval type.

The endpoint also highlights the distinction between immunogenicity measures and clinical outcomes. HAI and MN titers describe laboratory antibody responses, summarized as geometric means. Such measures allow a comparison of biological responses, but they are not a direct count of influenza illness. Clear interpretation requires keeping the measured outcome separate from broader language about protection.

The record includes multiple outcome measures and analyses, along with a secondary assessment of persistence at 6 months. Multiple endpoints, assays, and time points make prespecification and transparent reporting important. Without an analysis hierarchy or multiplicity plan, readers cannot tell how results across those analyses were intended to support an overall conclusion.

The planning illustrations also show why sample-size calculations need careful labeling. Calculations based on an observed effect can help illustrate what sample sizes correspond to particular assumptions, but they are not the original design rationale and are not observed power. Distinguishing those uses prevents a retrospective calculation from being mistaken for evidence that the study was adequately or inadequately designed.

Finally, the record illustrates the limits of registry-level interpretation. Design features and outcome intentions are available, while crucial elements for evaluating the primary inference—including the margin, estimates, interval limits, and analysis populations—are not reported. Transparent reporting of those elements is necessary for readers to assess the strength and scope of a non-inferiority conclusion.

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 most consequential limitation for interpreting this trial from the registry record is the absence of numerical primary outcome results. The record describes geometric mean titers and 95% confidence intervals, but does not report the estimates or interval limits. It also does not give the non-inferiority margin. These omissions prevent an assessment of whether the intended primary criterion was met.

The primary outcome description covers HAI and MN titers and identifies a 30-day timeframe, while also referring to baseline and one-month post-vaccination measurements. The record does not specify the exact contrast used for each analysis, how multiple assay results were prioritized, or how repeated measurements were handled. It notes that the endpoint has several categories or time points and is not reduced to one comparison, leaving no single primary numerical comparison for interpretation.

Other important trial details are not reported in the registry record: the randomization procedure, allocation ratio, masking recipient, analysis populations, missing-data approach, and original sample-size justification. The record also does not provide the statistical analysis plan or a multiplicity strategy despite listing three outcome measures and 18 analyses. These gaps limit assessment of bias, precision, and robustness.

The safety information is similarly limited to event counts and at-risk denominators for serious and other adverse events. Event descriptions, definitions, follow-up details, and deaths are not reported. The adverse-event counts therefore cannot stand in for a complete safety analysis.

Finally, the primary endpoint is an antibody-titer measure. The registry does not report a primary clinical influenza outcome, so interpretation should remain within the scope of the immunogenicity question described. None of these reporting limitations establishes what the unreported results would have shown.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Randomized Trial of High Dose Influenza Vaccine in Long Term Care Setting — NCT01654224.
• Registry record last updated 2017-07-02; status last verified 2017-06.
• Results first posted 2016-07-14.
• 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 trial randomized residents of long-term care settings to high-dose or standard-dose inactivated influenza vaccine. The registry lists enrollment of 205, identifies the study as single-masked and parallel-group, and gives a start date of 2011-11 and primary completion date of 2014-06.

The primary objective was non-inferiority based on HAI and MN titers, comparing baseline with one month after vaccination. Geometric mean titers and 95% confidence intervals are specified, but numerical primary results and the non-inferiority margin are not reported in the registry record. A secondary outcome concerns persistence at 6 months.

The adverse-event entries list zero affected for serious and other adverse events in both vaccine groups, with at-risk denominators of 89 for HD IIV and 98 for SD IIV. Deaths are not reported in the registry record. The record lists three outcome measures and 18 analyses but does not describe the analysis populations, missing-data methods, multiplicity plan, or original sample-size justification.