A Clinical Trial of CSL's 2010/2011 Formulation of Enzira® in a Healthy Adult Population: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for A Clinical Trial of CSL's 2010/2011 Formulation of Enzira® in a Healthy Adult Population (NCT01113580), a non-randomized phase 4 study. The primary outcome is The Percentage of Evaluable Participants Achieving Seroconversion or Significant Increase in Antibody Titre..

2. Clinical Question

3. Trial Design

This completed Phase IV study was described as a single-centre, open-label study of the 2010/2011 formulation of Enzira®. It enrolled 120 healthy volunteers and used a parallel, non-randomized design. The two groups were adults aged 18 to 59 years and older adults aged 60 years or older. The record lists 60 participants at risk in each group for the adverse-event summaries.

All participants received the same named vaccine intervention. The age groups therefore provide separate descriptions of outcomes in different populations, not a randomized comparison of vaccine against placebo or another vaccine. Because allocation was non-randomized, the groups should not be treated as if they were exchangeable at baseline. Differences in their outcomes, if reported, could be associated with other group characteristics as well as age.

The study was open-label, meaning masking was not used. The record does not describe blinded outcome assessment or other steps to reduce the influence of participants' or researchers' knowledge of vaccination. The listed primary endpoint is an antibody response measured approximately 21 days after vaccination. Listed secondary outcomes concern solicited and unsolicited adverse events.

The start and primary completion are both recorded as 2010-05, and the study status is completed. A fuller account of recruitment, vaccination procedures, follow-up visits, and the operational definition of the single centre is not reported in the registry record. The record also does not report a protocol-level sample-size justification or a statistical analysis plan. These omissions limit how fully the intended conduct can be reconstructed from the registry entry alone.

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:

Analysis population for the primary outcome, as defined in the registry: The Evaluable Population comprised all participants who were vaccinated with the study vaccine, provided both pre- and post-vaccination antibody titre results, and were not excluded from the analyses (eg, for the use of a prohibited medication or a laboratory-confirmed influenza virus infection between Visits 1 and 2).

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 The Percentage of Evaluable Participants Achieving Seroconversion or Significant Increase in Antibody Titre., measured over Approximately 21 days after vaccination.

The primary endpoint is the percentage of evaluable participants who achieved seroconversion or a significant increase in antibody titre. It uses haemagglutination inhibition (HI) antibody titres and applies the criteria described in the registry record. For participants whose pre-vaccination HI titre was < 10, seroconversion is defined by a post-vaccination titre of ≥ 40. For participants whose pre-vaccination titre was ≥ 10, a four-fold or greater increase is considered significant.

This type of endpoint is used to describe an immune response to vaccination, rather than a clinical influenza outcome. Reporting a percentage gives the proportion of participants meeting the stated antibody criterion, while a confidence interval communicates uncertainty around that estimate. The endpoint is defined for an evaluable population: participants had to be vaccinated, provide both pre- and post-vaccination titre results, and not be excluded from analysis. The registry record gives examples of exclusions, including use of a prohibited medication or a laboratory-confirmed influenza virus infection between assessments, but the full criteria are not reported in the registry record.

The stated assessment time is approximately 21 days after vaccination. Numerical results for the primary endpoint, including group percentages and confidence intervals, are not reported in the registry record. Consequently, the endpoint definition can be described, but the observed immune-response proportions and their precision cannot be interpreted.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does the primary percentage represent?

The endpoint is a binary classification for each evaluable participant: the participant either meets the specified antibody-response criterion or does not. The group percentage is a summary of the share classified as having seroconverted or having a significant increase in titre. It is not a measure of the size of the antibody increase for every participant. The threshold rules use the pre-vaccination titre to determine which response criterion applies.

General statistical explanation: a percentage is an estimate of the underlying proportion in a population, based on the participants observed. The estimate can vary from sample to sample. A confidence interval expresses this sampling uncertainty, subject to the assumptions of its calculation. A 95% confidence interval is a method-based interval; it does not mean that 95% of individual participants' responses fall within the interval. The record specifies a 95% confidence interval but does not report the calculated interval or its construction method.

Why define an evaluable population?

The primary endpoint requires both a pre-vaccination and a post-vaccination titre, because the response classification depends on comparing measurements or applying a post-vaccination threshold in relation to baseline. The registry's evaluable-population description also excludes some participants, with examples involving prohibited medication and laboratory-confirmed influenza infection between assessments. This makes the analyzed population narrower than the full set of enrolled participants may be. The number of participants excluded, the reasons for exclusion by group, and the actual primary endpoint denominators are not reported in the registry record.

General statistical explanation: excluding participants can affect both the precision and the interpretation of an estimate. If participants without complete measurements differ systematically from those with measurements, the evaluable group may not represent everyone enrolled. The record does not describe an imputation method or sensitivity analysis for missing titres, so it is not possible to assess how incomplete measurements were handled beyond the evaluable-population definition.

What can the age-group structure establish?

The parallel groups describe adults and older adults who received the same vaccine formulation. They are not randomized to different treatments, and there is no listed control arm. A comparison of group percentages, if available, would be an observational comparison between age-defined groups. Differences could reflect age-related or other group differences, and the record does not report adjusted analyses that might address measured characteristics.

General statistical explanation: random allocation helps balance known and unknown participant characteristics across treatment groups on average. Without randomization, that protection is absent. This does not prevent descriptive summaries, but it limits causal interpretation of differences between groups. Here, numerical primary endpoint comparisons and adjusted analyses are not reported in the registry record.

How should the safety counts be read?

The safety fields list participants at risk and participants affected by serious and other adverse events. These are participant counts, not event counts: one participant could potentially have more than one event, but event-level detail is not given. The record lists zero affected by serious adverse events in each group and provides other-event counts of 22 and 15. It does not give the event terms, the number of individual events, exposure-adjusted rates, or a full account of severity and timing. The listed secondary outcomes include frequency of solicited adverse events and frequency and intensity of unsolicited adverse events, but numerical results for those named outcomes are not reported in the registry record.

General statistical explanation: absence of a recorded event among participants in a study does not by itself establish that the event cannot occur. The amount of information about uncommon events depends on the number observed and the amount of follow-up, among other factors. Follow-up duration for safety outcomes is not reported in the registry record, so the scope of safety surveillance cannot be fully assessed.

What do the planning calculations mean?

The record describes a sample-size planning illustration based on the observed effect, with a two-sided significance level of 0.05, equal allocation, and a normal approximation. It describes the target effect as a stated fraction of the observed effect. These are planning assumptions, not evidence that the original study was designed using those assumptions, and the registry record does not report the trial's own sample-size justification.

General statistical explanation: sample-size calculations estimate how many participants might be needed under specified assumptions to detect a target effect with a chosen statistical procedure. A calculation based on an observed effect is sensitive to the estimate used and should not be read as observed power or as proof that the original study had adequate precision. The record does not report the numerical planning outputs in the registry record for this analysis, so no required sample size can be interpreted.

10. Multiplicity, Missing Data and Analysis Populations

The record lists a primary antibody endpoint and secondary safety outcomes. It also reports five outcome measures in total, but gives no analyses. When several outcomes are examined, the chance of at least one apparently unusual result can increase if each is assessed separately without accounting for multiplicity. This is a general statistical concern, not evidence that a particular adjustment was or was not applied. Any multiplicity procedure, endpoint hierarchy, or prespecified testing strategy is not reported in the registry record.

The primary endpoint is defined for an evaluable population requiring pre- and post-vaccination titre results and the absence of specified exclusions. The record gives examples of exclusions but does not report the complete analysis-population rules, the number excluded, or the number analyzed in each group. It also does not report how missing titre measurements were handled, whether missingness was assessed by reason, or whether any sensitivity analyses were performed.

The safety outcomes are named, but the registry record does not provide numerical results for the solicited-event outcome or the frequency and intensity of unsolicited events as named endpoints. The event counts in the safety summary are not accompanied by a detailed analysis plan. No interim analyses, stopping rules, or multiplicity handling are reported in the registry record. Without these details and the primary endpoint estimates, the statistical analysis cannot be independently reconstructed from the registry entry.

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 2.0% reporting threshold.

Most frequent non-serious adverse event terms

The registry's serious adverse-event summary lists 0 affected participants among 60 at risk in the adults group and 0 among 60 at risk in the older adults group. These are the counts recorded for serious adverse events; the record does not provide event terms or an explanatory narrative. Death counts are not reported in the registry record.

The same summary lists 22 participants with other adverse events among 60 at risk in the adults group and 15 among 60 at risk in the older adults group. The record does not clarify the event-level details attached to these counts, including the specific terms, timing, intensity, duration, or relationship to vaccination. The listed secondary outcomes refer to solicited events and unsolicited events, but the counts in the summary should not be assumed to provide all details for those outcomes.

General statistical explanation: a zero count in a study is a description of what was observed in that study, not proof that the event is impossible or that risk is absent. Interpretation also depends on how events were defined, collected, and followed. Those details are not reported in the registry record, so the safety figures should be read as limited descriptive information rather than as a complete estimate of safety.

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

The record documents a completed study of a seasonal influenza vaccine formulation in healthy adults, organized into adults and older adults groups. Its primary endpoint is an antibody-response percentage assessed approximately 21 days after vaccination, using stated HI titre criteria. The record also identifies adverse-event outcomes and gives limited adverse-event counts by group.

What the record does not provide is the numerical result for the primary antibody endpoint. It therefore does not show what proportion of evaluable participants met the response definition, how estimates differed between groups, or how precise those estimates were. The absence of those results in the registry record should not be interpreted as a zero response or as evidence of no response.

The study's structure also matters. Participants were not randomized between the age groups, and the listed groups did not receive different interventions. As a result, the design does not support treating the groups as controlled treatment comparisons. A descriptive difference between them, were one reported, would not by itself establish that age caused the difference.

The safety information is similarly limited. Zero serious adverse events are listed in each group, while other adverse-event counts are also recorded. Those entries do not include the details needed to characterize the events fully or to determine attribution. They do not establish that no risk exists.

General statistical explanation: statistical results are most informative when estimates are accompanied by uncertainty measures and when the analysis population and methods are clear. The registry record gives some endpoint definitions but no primary estimates, confidence intervals, analysis details, or complete missing-data account. The posted information can describe the intended questions and selected counts, but it cannot support a full assessment of the magnitude, precision, or comparative meaning of the immunogenicity findings.

13. Why This Trial Matters Statistically

This study illustrates why endpoint definitions and numerical results need to be read together. The primary outcome is specified as a percentage meeting a defined HI antibody-response criterion, with different rules depending on the pre-vaccination titre. That definition makes clear what was intended to count as a response. Without the reported percentage and its confidence interval, however, readers cannot assess the observed response level or its precision.

The study also demonstrates the difference between parallel groups and randomized comparison arms. Adults and older adults were studied separately, but allocation was non-randomized and both groups received the same named vaccine. This structure can support descriptions by age group, but it does not create a like-for-like control comparison. Statistical wording should reflect that design rather than imply a causal contrast.

The evaluable-population definition highlights another important issue: an endpoint may be based on fewer participants than were enrolled if complete measurements or other analysis requirements are needed. The record describes some eligibility for the analysis but does not report the actual analyzed counts or missing-data handling. Those details are important when evaluating how representative and precise an estimate may be.

Finally, the safety summary shows why event counts need context. Participant counts alone do not communicate event types, timing, intensity, or attribution. The registry record offers some descriptive safety information, but not enough detail for a complete statistical assessment. These are general lessons in interpreting registry records: study design, analysis population, outcome definition, uncertainty, and result availability all shape what conclusions are justified.

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 important limitation for statistical interpretation is that numerical results for the primary antibody endpoint are not reported in the registry record. Without the group estimates and 95% confidence intervals, the immune-response findings cannot be evaluated for magnitude or precision. The record lists five outcome measures and no analyses, leaving the reported endpoint definitions without corresponding numerical results in the information available.

The study was non-randomized, open-label, and single-centre. The age groups are not randomized control groups, so comparisons between them would be vulnerable to differences beyond age. Masking was not used. Whether any other protections against measurement or reporting bias were applied is not reported in the registry record.

The primary outcome uses an evaluable population, but the full analysis-population details, actual denominators, exclusions, and missing-data methods are not reported in the registry record. The duration and completeness of follow-up are also not described in the available record. These gaps make it difficult to assess selection into the endpoint analysis or the scope of adverse-event collection.

The adverse-event summary gives participant counts but lacks detailed event terms and other context. Death counts are not reported in the registry record. The record does not report a trial-specific sample-size justification, a full statistical analysis plan, multiplicity procedures, or interim analyses. These limitations concern what can be learned from the registry record; they do not establish that the information was absent from other study documents.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: A Clinical Trial of CSL's 2010/2011 Formulation of Enzira® in a Healthy Adult Population — NCT01113580.
• Registry record last updated 2017-11-21; status last verified 2017-10.
• Results first posted 2012-07-18.
• 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

NCT01113580 is a completed Phase IV, single-centre, open-label, non-randomized parallel study of CSL's 2010/2011 Formulation of Enzira® Vaccine. It enrolled 120 healthy volunteers in two groups: adults aged 18 to 59 years and older adults aged 60 years or older. Both groups received the same named intervention.

The primary endpoint was the percentage of evaluable participants achieving seroconversion or a significant increase in antibody titre, assessed approximately 21 days after vaccination. The registry record lists safety outcomes and adverse-event counts, including zero serious adverse events among 60 at risk in each group. It does not report numerical primary endpoint results, the primary analysis denominators, or detailed event descriptions. The record also does not report a trial-specific sample-size justification or a full statistical analysis plan.