This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for Annual Study to Investigate Inactivated Subunit Influenza Vaccine Due to New Virus Strains for the Southern Hemisphere 2015 Season (NCT02381418), a na phase 3 study. The primary outcome is the Serum Antihemagglutinin Antibody Titers and the Derived Parameters Defined in the Committee for Medicinal Products for Human Use (CHMP) Note for Guidance on Harmonization of Requirements for Influenza Vaccines for Influenza Vaccines..
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT02381418 |
| Phase | Phase 3 |
| Condition | Influenza |
| Allocation | Not applicable (single group) |
| Design model | Single Group |
| Masking | None (open label) |
| Enrollment | 120 |
| Arms in the primary outcome | n/a |
| Lead sponsor | Abbott |
| Results posted | Yes |
2. Clinical Question
Population
Healthy adults aged ≥ 18 and ≤ 60 years and elderly adults aged ≥ 61 years. The registry record gives the study's total enrollment as 120 but does not report how many participants were in each age group.
Intervention
Trivalent influenza subunit vaccine Influvac®, described as 3x 15mcg Hemagglutinin Antigen (HA) per 0.5 ml, given as one injection at Day 1.
Comparator
There is no concurrent control arm. The registry record calls the study baseline-controlled, but does not report the details of how baseline measurements were used as a comparison.
Primary question
Three weeks after vaccination, what are the seroprotection and seroconversion rates for A/H1N1, A/H3N2, and B strains in the adult and elderly groups, as part of the assessment of antibody responses to the vaccine composition for the Southern Hemisphere 2015 season?
This is a question about the measured antibody response after vaccination, not a comparison of vaccine against placebo or another vaccine. The registry describes serum antihemagglutinin antibody titers and derived parameters aligned with the Committee for Medicinal Products for Human Use guidance on influenza vaccines. The specific numerical results for the listed strains and age groups are not reported in the registry record. Accordingly, the record supports describing the study question and outcome framework, but not stating the observed response rates or comparing the age groups.
3. Trial Design
The registry identifies this as a Phase 3 study with a single-group model and no masking. It is described as open-label and baseline-controlled. The intervention was the commercially available trivalent influenza subunit vaccine Influvac®, administered as one injection at Day 1. The listed formulation is 3x 15mcg Hemagglutinin Antigen (HA) per 0.5 ml. The stated purpose was to investigate the immunogenicity, safety, and tolerability of the changed vaccine virus composition in healthy adults and elderly adults.
The two age groups were adults aged ≥ 18 and ≤ 60 years and elderly adults aged ≥ 61 years. Enrollment was 120. The registry lists the study as completed, with start and primary completion both recorded as 2015-03. These details establish the population, intervention, and general structure, but do not provide participant counts by age group or a schedule of assessments beyond the primary outcome timeframe.
A single-group design does not create a concurrent randomized comparison. The baseline-controlled description indicates that baseline is relevant to the study's design, but the registry record does not describe the baseline measurement schedule, the comparison procedure, or whether the primary analysis formally compared post-vaccination values with baseline. Allocation is listed as NA, consistent with the absence of multiple allocated arms. Therefore, an observed response after vaccination cannot by itself separate vaccine-associated change from time trends, measurement variability, or other influences.
The primary outcome is described as antibody titers and derived parameters, with seroprotection and seroconversion rates assessed three weeks post vaccination. Safety and tolerability were also assessed, including unsolicited adverse events, reactogenicity, and overall inconvenience. Detailed procedures for outcome measurement, follow-up beyond the primary timeframe, and the 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.
Overall Study
| Stage | Influvac |
|---|---|
| STARTED | 120 |
| COMPLETED | 120 |
| NOT COMPLETED | 0 |
Analysis population for the primary outcome, as defined in the registry: Two subjects were excluded from the efficacy sample due to major protocol violations with a potential effect on immunogenicity outcome.
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.
| Characteristic | Unit | Influvac |
|---|---|---|
| Participants analysed | 120 | |
| Age, Categorical: <=18 years | Participants | 1 |
| Age, Categorical: Between 18 and 65 years | Participants | 71 |
| Age, Categorical: >=65 years | Participants | 48 |
| Age, Continuous: adult (18-60 year old) | years | 41.2 (18 to 60) |
| Age, Continuous: elderly adult (>=61 year old) | years | 71.5 (61 to 88) |
| Gender: Female | Participants | 58 |
| Gender: Male | Participants | 62 |
| Region of Enrollment: Australia | participants | 120 |
6. Primary Endpoint
The registry lists the primary outcome as the Serum Antihemagglutinin Antibody Titers and the Derived Parameters Defined in the Committee for Medicinal Products for Human Use (CHMP) Note for Guidance on Harmonization of Requirements for Influenza Vaccines for Influenza Vaccines., measured over 3 weeks post vaccination.
| Element | Registry entry |
|---|---|
| Result type | Number |
| Measure of spread | 95% Confidence Interval |
| Unit | percentage of subjects |
| Endpoint classification | Binary Endpoint |
The primary endpoint concerns serum antihemagglutinin antibody response to A/H1N1, A/H3N2, and B strains, assessed three weeks post vaccination. The registry describes the outcomes as seroprotection and seroconversion rates in non-elderly adults and elderly adults. The unit is percentage of subjects, and the stated dispersion measure is a 95% confidence interval. The endpoint is linked to derived parameters described in the Committee for Medicinal Products for Human Use guidance on harmonization of requirements for influenza vaccines.
In general, seroprotection rates describe the share of a group meeting a specified antibody protection criterion, while seroconversion rates describe the share meeting a specified criterion for antibody response relative to baseline. These are general descriptions: the exact thresholds, laboratory assay, and operational definitions used in this study are not reported in the registry record. The endpoint is used to characterize an immune response, not to directly measure prevention of influenza illness.
Reporting percentages with confidence intervals would show both the estimated response proportion and its statistical uncertainty. The record names the 95% confidence interval as the dispersion measure but does not include the numerical estimates or interval limits for the strain-by-age outcomes. The observed size and precision of those responses therefore cannot be assessed from the registry record.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record identifies a completed single-group study with enrollment of 120 and a primary assessment three weeks post vaccination. Its primary question concerns seroprotection and seroconversion for A/H1N1, A/H3N2, and B strains in adults and elderly adults. However, the numerical primary outcome results are not reported in the registry record. No response percentages, antibody titers, confidence interval limits, or between-age-group comparisons are available in the record. It is therefore not possible to characterize the magnitude or precision of the observed immunogenicity results from these data.
The description of the endpoint alone does not establish that a particular response rate was reached. Nor does it establish whether response rates differed by age group or strain. The study's antibody measures are outcomes of interest, but the registry record does not include the estimates needed to interpret their distribution. The stated 95% confidence interval is a measure intended to convey uncertainty around a percentage; without the estimates and interval limits, that uncertainty cannot be evaluated.
The study has no concurrent comparator arm and is not described as randomized. A baseline-controlled design can include a before-and-after perspective, but the registry record does not explain how baseline values entered the analysis. Even with baseline values, a single-group study does not provide the same protection against alternative explanations as a randomized comparison. This limits causal interpretation of any change in antibody measurements, particularly when details of the analysis are unavailable.
For safety, the record lists 0 participants with serious adverse events among 120 at risk and 19 participants with other adverse events among 120 at risk. It lists no top serious adverse-event terms. Deaths are not reported in the registry record. These entries describe what is recorded in the safety fields; they do not provide event timing, severity beyond the serious-event classification, relatedness assessments, or a detailed account of the other adverse events. They should not be treated as a complete characterization of all possible safety outcomes.
The registry states that two subjects were excluded from the efficacy sample because of major protocol violations with a potential effect on immunogenicity outcome. It does not provide further detail on the violations, the exact analysis population, or how missing observations were handled. Since the primary outcome estimates are absent, the effect of those exclusions on the results cannot be assessed. Overall, the record describes the study question and some design and safety information, but it does not supply enough outcome data to judge the size, precision, or pattern of the measured antibody responses.
9. Statistical Methods Explained
What does a percentage endpoint represent?
The primary outcome is expressed as a percentage of subjects. In general, a percentage for an event or response is the number of participants meeting the outcome definition relative to the relevant analysis group. For this study, the outcomes are seroprotection and seroconversion rates for three influenza strains, with results described for non-elderly adults and elderly adults. The exact outcome thresholds and the group denominators used for each estimate are not reported in the registry record, so the numerical rates cannot be reconstructed.
Percentages are often easier to compare across groups of different sizes than raw counts, but they do not show the underlying precision by themselves. A percentage based on a limited number of observations can be uncertain. The registry names 95% confidence intervals as the dispersion measure. In general, a confidence interval describes uncertainty in an estimate under the assumptions of the analysis; it does not guarantee that the interval contains a true value, nor does it communicate the clinical importance of a response. Since neither point estimates nor interval limits are reported, the uncertainty in the primary outcomes cannot be inspected.
What do seroprotection and seroconversion mean?
These are antibody-response measures. In general, seroprotection classifies participants according to whether measured antibody meets a chosen protection criterion. Seroconversion classifies participants according to whether their antibody response meets a chosen change criterion relative to baseline. Such criteria depend on formal definitions and laboratory measurements. The registry record does not report the specific thresholds, assay procedures, or detailed calculation rules for this study. It refers to derived parameters defined in Committee for Medicinal Products for Human Use guidance, but that reference does not give the study's actual numerical results.
The outcomes are evaluated for A/H1N1, A/H3N2, and B strains and in two age groups. Separate strain and age-group estimates can describe patterns that a combined result might conceal. However, the record does not report those estimates or explain whether the analyses were designed to test differences between strains or age groups. Describing outcomes separately is not the same as evidence of a statistically tested subgroup difference.
Why does study design matter to interpretation?
This is a single-group, open-label study with no masking. The registry describes it as baseline-controlled, but does not report the measurement schedule or analytical role of baseline. In general, a baseline measurement can provide a within-participant reference. A before-and-after change, however, is not equivalent to a randomized comparison with a concurrent control group. Without a control group, changes may also reflect factors other than the intervention, and open-label conduct can affect subjective assessments such as tolerability reporting.
The study is not a randomized comparison, so randomized allocation methods and treatment-arm balance do not apply. The record lists one intervention and no comparison arm. Any planning illustration based on equal allocation between two arms is a hypothetical planning calculation, not a description of the study's actual design. The registry's stated planning assumptions include a two-sided significance level of 0.05 and a normal approximation, with the effect defined as a fraction of an observed effect. Such planning values are not observed power and do not add outcome evidence. The record does not report a sample-size justification for the actual single-group study.
How should confidence intervals and significance be understood?
In general, a confidence interval presents a range of values compatible with an estimate under a specified statistical procedure and its assumptions. Its width depends on factors including the amount of information and variability in the data. A narrower interval generally indicates greater precision for that estimate, while a wider interval indicates more uncertainty. This is a general explanation; the registry record does not provide the intervals for the study outcomes.
A significance test and a confidence interval answer related but distinct questions. A test evaluates a statistical hypothesis under specified assumptions, whereas a confidence interval emphasizes the range and precision of plausible estimates. Neither alone determines clinical importance. The registry record does not report primary-outcome test statistics, p-values, adjustment procedures, or an analysis plan. It is therefore not possible to state whether a statistical threshold was met or what inferential procedure was used.
Why can over-dispersion matter?
In general, a binomial model treats each participant's outcome as an event or non-event and uses a specified probability to describe the event rate. If outcomes vary more than the model expects, the data are over-dispersed relative to that model. Ignoring over-dispersion can make uncertainty appear smaller than it is, leading to confidence intervals that are too narrow or tests that appear more decisive than warranted. This concept may matter when modeling proportions, especially when observations are clustered or participants differ in ways the model does not capture. The registry record does not state that over-dispersion was assessed or that a particular model was used.
There is also no analysis record listed in the registry. The statistical methods used to produce outcome estimates, handle repeated measurements, or account for the two age groups are not reported in the registry record. General statistical principles can explain what those methods would be intended to address, but cannot identify methods actually used in this study.
10. Multiplicity, Missing Data and Analysis Populations
The primary outcome description includes seroprotection and seroconversion, three strains, and two age groups. Considering several outcomes can raise a multiplicity question: when many estimates or statistical tests are examined, the chance of at least one apparently unusual result may increase if each test is treated separately. This is a general statistical concern, not evidence that the study's analysis produced a false-positive finding. The registry record does not report a multiplicity strategy, a hierarchy of outcomes, or whether any formal tests were performed.
The record lists three outcome measures, but does not give their complete definitions or numerical results. It also does not report a statistical analysis plan, test procedures, or analysis populations beyond identifying the efficacy sample and safety denominators. Therefore, it is not possible to determine whether outcomes were prespecified in detail, whether adjustments were made, or how results were selected for reporting.
For the efficacy sample, two subjects were excluded because of major protocol violations with a potential effect on immunogenicity outcome. The exact analysis denominator, reasons in more detail, and the handling of missing measurements are not reported in the registry record. There is no description of imputation, sensitivity analyses, or how participants without an endpoint measurement were treated. The enrollment count of 120 should not be assumed to be the denominator for every efficacy estimate.
Safety information is presented for 120 participants at risk in the listed categories. The record does not describe missing safety observations or the duration and completeness of safety follow-up. These omissions limit assessment of whether all participants contributed equally to each outcome. They also prevent evaluation of how exclusions or unavailable measurements might affect interpretation.
11. Safety Results
The registry reports serious adverse events as affected participants divided by participants at risk.
| Arm | Participants with serious adverse events | Participants at risk | Percentage |
|---|---|---|---|
| Influvac | 0 | 120 | 0.0% |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 0% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Influvac | 19 of 120 |
Most frequent non-serious adverse event terms
| Event term | Organ system | Influvac |
|---|---|---|
| vaccine site pain | General disorders | 7 of 120 |
| oropharyngeal pain | Respiratory, thoracic and mediastinal disorders | 4 of 120 |
| nasal congestion | Respiratory, thoracic and mediastinal disorders | 3 of 120 |
| fatigue | General disorders | 3 of 120 |
| malaise | General disorders | 3 of 120 |
| vaccination site warmth | General disorders | 3 of 120 |
| application site pruritus | General disorders | 2 of 120 |
| cough | Respiratory, thoracic and mediastinal disorders | 2 of 120 |
| headache | Nervous system disorders | 2 of 120 |
| nasopharyngitis | Respiratory, thoracic and mediastinal disorders | 1 of 120 |
The registry lists 120 participants at risk for serious adverse events and 0 participants affected. It also lists 120 at risk for other adverse events and 19 participants affected. No top serious adverse-event terms are listed. The death field has no reported value, so deaths are not reported in the registry record.
These figures should be read as registry entries for the listed categories. The record does not supply a detailed description of the events, their timing, duration, severity beyond the serious-event category, or whether investigators considered them related to vaccination. It also does not report how adverse events were collected or the length of safety follow-up. The 19 participants recorded with other adverse events do not, by themselves, establish a cause or indicate whether any event was expected.
A zero count in the serious-event field means no affected participants are recorded in that field; it does not establish that serious events are impossible or that the vaccine has no safety risks. Similarly, missing death information should not be interpreted as a confirmed absence of deaths. These limitations are especially important when reading safety summaries from a single study, because the registry entries do not provide a full clinical narrative or a comparison group.
12. What the Result Does, and Does Not, Mean
The record establishes that a Phase 3, open-label, single-group study of Influvac® enrolled 120 participants, including adults and elderly adults, and defined antibody outcomes three weeks after vaccination. It also records safety information for the listed adverse-event categories and notes that two subjects were excluded from the efficacy sample for major protocol violations with a potential effect on immunogenicity outcome.
It does not report the numerical seroprotection or seroconversion results, antibody titers, confidence interval limits, or comparisons between age groups or strains. As a result, the size and precision of the measured antibody response cannot be described from the registry record. The endpoint definitions and laboratory details are also incomplete, so the criteria underlying the response classifications cannot be independently assessed using the record alone.
The study's single-group design does not provide a randomized concurrent comparison. The baseline-controlled label does not, by itself, explain how baseline values were used or resolve the limits of causal interpretation. The record therefore cannot establish that changes in antibody measurements were caused solely by vaccination, or support a comparative claim against another vaccine or no vaccination.
The safety entries report 0 participants with serious adverse events and 19 with other adverse events among 120 at risk in each listed category. These counts do not give event details, causal attribution, or complete follow-up information. Deaths are not reported in the registry record. The entries describe recorded observations rather than proving absence of risk.
In short, the registry documents the study's population, intervention, endpoint framework, and selected safety counts. It does not provide the outcome estimates or analytical details needed to determine the magnitude, precision, or comparative meaning of the antibody findings.
13. Why This Trial Matters Statistically
This study illustrates the distinction between a clearly described research question and a complete statistical result. The registry defines antibody response outcomes by strain, age group, and assessment time, and states that results are expressed as percentages with 95% confidence intervals. Those details identify what the investigators intended to measure. Without the actual estimates and intervals, however, readers cannot assess response magnitude or precision.
The single-group structure also matters. Baseline information may be useful for describing participants before vaccination, but the registry record does not specify how baseline measurements were used. A study without a concurrent comparator cannot make the same direct between-group assessment as a randomized trial. This is an important design consideration when interpreting any before-and-after outcome, and it applies even when the intervention and measurement schedule are clearly described.
The endpoint spans multiple strains and age groups. In general, this breadth can be useful for characterizing whether patterns differ across outcomes, but it also makes transparent definitions and analysis plans important. The record does not report the detailed criteria, multiplicity approach, or statistical methods. Readers consequently cannot determine how results would have been combined, compared, or adjusted for uncertainty across outcomes.
The safety fields show how registry summaries can be informative while remaining limited. They give counts for serious and other adverse events, but do not include event narratives or attribution. That makes precise wording essential: recorded counts can be stated, while conclusions about cause, completeness, or broader safety cannot be drawn from those counts alone.
For biostatistical interpretation, this record is a reminder to distinguish design information, defined endpoints, recorded safety data, and numerical efficacy findings. They are not interchangeable. Here, the endpoint framework is described, but its main numerical results are not reported in the registry record.
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 direct limitation is that numerical primary outcome results are not reported in the registry record. Although the endpoint description specifies seroprotection and seroconversion rates for A/H1N1, A/H3N2, and B strains three weeks post vaccination, the record does not give the rates, antibody titers, confidence interval limits, or age-group-specific estimates. The magnitude and precision of the immune responses therefore cannot be evaluated.
The registry does not report the exact seroprotection and seroconversion definitions, assay procedures, or threshold criteria. It refers to guidance for derived antibody parameters, but does not show how those definitions were operationalized for this study. Participant counts within each age group and the denominators for the efficacy estimates are also not reported. Two subjects were excluded from the efficacy sample because of major protocol violations with a potential effect on immunogenicity outcome, but the registry gives no further detail about the violations or analysis handling.
The single-group, open-label design has no concurrent comparison arm. The baseline-controlled label is not accompanied by a description of how baseline measurements were analyzed. This restricts comparative and causal interpretation. In addition, the record does not include the statistical analysis plan, detailed analysis methods, multiplicity procedures, or approaches to missing data. It is not possible to determine whether or how these issues were addressed.
Safety information is limited to counts in listed categories. Event descriptions, timing, follow-up duration, relatedness assessments, and death results are not reported in the registry record. The registry also does not explain whether all participants completed safety follow-up. These limitations mean that the available safety counts should not be treated as a comprehensive account of events or as evidence about their cause.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Annual Study to Investigate Inactivated Subunit Influenza Vaccine Due to New Virus Strains for the Southern Hemisphere 2015 Season — NCT02381418.
- Registry record last updated 2016-12-22; status last verified 2016-10.
- Results first posted 2016-12-22.
- 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.
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18. Record Summary
The registry describes a completed Phase 3, open-label, single-group study of trivalent influenza subunit vaccine Influvac® in healthy adults aged ≥ 18 and ≤ 60 years and elderly adults aged ≥ 61 years. Enrollment was 120, and the recorded start and primary completion were both 2015-03. One injection was administered at Day 1.
The primary outcome was serum antihemagglutinin antibody response, including seroprotection and seroconversion rates for A/H1N1, A/H3N2, and B strains three weeks post vaccination. Numerical primary outcome results and detailed statistical methods are not reported in the registry record. Two subjects were excluded from the efficacy sample for major protocol violations with a potential effect on immunogenicity outcome.
The safety record lists 0 participants with serious adverse events and 19 with other adverse events, each among 120 at risk. Deaths are not reported in the registry record.