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 Prophylactic Efficacy of Relenza Against Influenza A and B (NCT01156701), a registered phase not stated study. The primary outcome is Number of Patients With Influenza.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT01156701 |
| Phase | Phase not stated |
| Condition | Pulmonary Disease, Chronic Obstructive, Bronchospasm, Influenza, Human |
| Allocation | Not Stated |
| Design model | Not Stated |
| Masking | Not Stated |
| Enrollment | 171705 |
| Arms in the primary outcome | n/a |
| Lead sponsor | GlaxoSmithKline |
| Results posted | Yes |
2. Clinical Question
The study asks whether influenza and respiratory outcomes differ between people dispensed Relenza for prophylaxis and people not receiving prophylaxis, in households where an index case had a medical visit associated with influenza. Its primary outcome is the number of patients with influenza. The registry record also identifies asthma, pneumonia, bronchitis, and any respiratory diagnosis as secondary outcomes.
The population described for the primary outcome consists of people at least 5 years old with at least 6 months of continuous enrollment in the Normative Health Informatics insurance claims database during influenza seasons from 2006-2009, described as October-April. The cohort descriptions distinguish people receiving prophylactic Relenza according to whether the household index case was treated for influenza, and people not receiving prophylaxis according to the same index-case distinction. The study summary describes assessing 30-day risk after a household member’s medical visit associated with influenza.
The resulting question is observational: among eligible people in these household circumstances, how often were influenza and respiratory diagnoses recorded in the different prophylaxis and index-case groups? It is not a randomized comparison. The registry record does not state how treatment allocation occurred, and the listed cohorts should not be assumed to be equivalent in their underlying characteristics. The study’s stated aims include assessing whether detailed analyses were feasible, describing outcome frequencies, and estimating direct, secondary, and total effects if analysis was feasible. Whether those aims were met, and the numerical results for the outcomes, are not reported in the registry record.
3. Trial Design
Despite the clinical-trial terminology sometimes used for studies of this kind, the registry describes a post-marketing observational study. GlaxoSmithKline is identified as the sponsor. The study was conducted in response to European regulatory authorities and was intended to assess Relenza when used as influenza prophylaxis. The registry lists the study as completed, with a start date of 2009-07 and primary completion in 2010-05.
The analysis uses insurance claims data from the Normative Health Informatics database. The primary-outcome population is described as people at least 5 years old with at least 6 months of continuous enrollment during influenza seasons from 2006-2009. The summary describes evaluating 30-day risk of influenza-like illness and respiratory outcomes in people whose household members had a medical visit associated with an influenza diagnosis. Cohort eligibility descriptions further distinguish prophylaxis status and whether an index case was treated. Some of those descriptions are truncated in the registry record, so their full eligibility definitions are not available.
The registry lists an enrollment of 171705. That figure is the study enrollment field; it does not establish the number of people in each cohort or the denominators used for each outcome. The registry also identifies 7 outcome measures and 50 analyses. It does not report numerical results for those analyses in the information available in the registry record.
No random allocation is stated. The registry explicitly warns that this is not a randomized comparison and that the arms are not a like-for-like control comparison. Consequently, the cohort contrasts may reflect differences in who received prophylaxis, household circumstances, or other factors, not only prophylaxis itself. The registry record does not report a protocol-level account of confounder adjustment, matching, or other steps used to make the groups comparable.
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 | Cohort 1: Prophylaxis With Untreated Index | Cohort 2: Prophylaxis With Treated Index | Cohort 3: Untreated With Untreated Index | Cohort 4: Untreated With Treated Index |
|---|---|---|---|---|
| STARTED | 257 | 1007 | 163716 | 6725 |
| COMPLETED | 257 | 1007 | 163716 | 6725 |
| NOT COMPLETED | 0 | 0 | 0 | 0 |
Analysis population for the primary outcome, as defined in the registry: The study population consisted of individuals who were at least 5 years old and had been continuously enrolled for at least 6 months in the Normative Health Informatics (NHI) insurance claims database during the influenza seasons of 2006-2009 (October-April).
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 | All Patients Included in the Analysis |
|---|---|---|
| Participants analysed | 171705 | |
| Age, Customized: 5-14 years | Participants | 47670 |
| Age, Customized: 15-44 years | Participants | 85640 |
| Age, Customized: 45-64 years | Participants | 37119 |
| Age, Customized: >=65 years | Participants | 1276 |
| Sex: Female, Male: Female | Participants | 84162 |
| Sex: Female, Male: Male | Participants | 87543 |
6. Primary Endpoint
The registry lists the primary outcome as Number of Patients With Influenza, measured over 2006-2009.
| Element | Registry entry |
|---|---|
| Result type | Number |
| Measure of spread | not applicable |
| Unit | patients |
| Endpoint classification | Binary Endpoint |
The primary endpoint is the number of patients with influenza. The registry describes it as the frequency of influenza among the four cohorts, with the outcome expressed as patients and the time frame identified as 2006-2009. This is a binary outcome at the individual level: a person is counted according to whether influenza is recorded or not, while the reported endpoint is a count of people with the event.
In general, counts and frequencies are useful for describing how often an outcome occurs in each group. They make the clinical event being compared explicit and can be an accessible starting point for assessing observed differences. Counts alone, however, do not establish whether groups had similar underlying risks. Interpreting a frequency also requires knowing the corresponding group denominator, the outcome definition, and how follow-up and eligibility were handled. Those details matter especially when group sizes differ or when people contribute different amounts of observation time.
The registry identifies the primary population as people at least 5 years old with at least 6 months of continuous enrollment in the claims database during the influenza seasons from 2006-2009. Claims-based diagnoses reflect recorded healthcare information; the registry record does not report validation details for the influenza definition or explain whether diagnosis required any particular combination of claims. It also does not give numerical counts or frequencies for the endpoint. The primary outcome’s intended role is therefore clear from its description, but its magnitude and the precision of any comparison cannot be assessed from the registry record alone.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record identifies a clinically relevant observational question and describes the populations and outcome categories, but it does not report numerical results for influenza or the secondary respiratory outcomes. There are no outcome counts, group denominators, effect estimates, or confidence intervals in the record information available for this analysis. As a result, it is not possible to describe the direction or size of an observed association, or how precisely an association was estimated, using the registry record alone.
The enrollment field reports 171705, but that number should not be treated as the denominator for every comparison. It does not show how many people entered each of the four cohorts, how many had each outcome, or whether all enrolled people contributed data to every analysis. Cohort-specific denominators and outcome counts are not reported in the registry record. The adverse-event fields list zero people at risk and zero affected in each listed cohort. With zero people at risk recorded, those fields do not provide evidence about the frequency of adverse events in the study population.
The study summary describes three intended analytical aims: assess feasibility, tabulate outcome frequencies, and, if feasible, estimate direct, secondary, and total effects. These are stated aims, not numerical findings. The registry record does not report whether detailed analysis was judged feasible or whether effect estimates were produced. Nor does it report the statistical model or adjustment strategy used to estimate effects. The intended causal language should therefore not be mistaken for proof that causal effects were established.
For an observational comparison, the meaning of a difference depends on how groups came to receive prophylaxis and on whether relevant factors were measured and accounted for. The registry does not state an allocation mechanism, and it cautions that the arms are not a like-for-like control comparison. Without reported group characteristics, adjusted estimates, or a detailed analysis plan, readers cannot determine from the registry record how much any hypothetical contrast might reflect differences between the groups rather than prophylaxis.
In general, an estimate describes the observed contrast, while a confidence interval describes the statistical uncertainty around that estimate under the analysis assumptions. Neither alone removes confounding or other design limitations. No effect estimates or confidence intervals are reported in the registry record, so their magnitude and precision cannot be interpreted. The study’s completion status and enrollment figure do not substitute for outcome results, and they do not establish whether the stated aims were achieved.
9. Statistical Methods Explained
The registry describes an observational analysis of insurance claims rather than a randomized allocation of Relenza. The primary outcome is a binary event summarized as the number of patients with influenza. The study also lists four respiratory outcomes and describes four cohorts formed by prophylaxis status and the treatment status of a household index case. The record lists 7 outcome measures and 50 analyses, but it does not give numerical results or a full account of the analytical methods.
What does a binary outcome describe?
In general, a binary outcome records whether a defined event occurred for each eligible person. A count of people with the event is one way to describe such data. To interpret the count as a frequency or risk, the denominator and follow-up period must also be clear. If people have different opportunities for an event to be recorded, comparisons may require methods that account for differences in observation. The registry identifies a 30-day risk analysis in its study overview and gives the primary outcome time frame as 2006-2009, but the record does not explain how the analysis reconciled the outcome window with the broader seasonal period or how follow-up was operationalized for each cohort.
The primary outcome is described as the number of patients with influenza. Secondary outcomes include the number of patients with asthma, pneumonia, bronchitis, and any respiratory diagnosis. The record does not provide the detailed claims algorithms, coding rules, or validation information used to define these events. Such definitions affect what an outcome count represents. For example, a diagnosis recorded in claims is not necessarily interchangeable with an independently confirmed clinical event; the registry record does not report confirmation procedures.
Why distinguish the household index case?
The four cohort descriptions separate people receiving prophylaxis from those not receiving it, and also distinguish whether the household index case was treated. This structure reflects the study’s stated interest in both prophylaxis and possible effects among household members when an index case receives treatment. The study summary describes people with a household member’s medical visit associated with influenza and a 30-day risk period. These categories define the comparisons of interest, but they do not by themselves make groups comparable. The registry record does not report randomization, and it cautions that the arms are not a like-for-like control comparison.
In general, confounding occurs when factors related to both group membership and outcome can contribute to an observed association. In an observational claims analysis, the source of treatment decisions and the measured characteristics of each group are important to interpreting contrasts. Adjustment can address measured differences under specified assumptions, but it cannot guarantee removal of unmeasured confounding. The registry record does not report which covariates, if any, were included in adjusted analyses, how missing covariates were handled, or whether any balance checks were performed.
How should uncertainty be read?
In general, a point estimate gives a single summary of an observed contrast, and a confidence interval gives a range of values compatible with the data and the method’s assumptions. A wider interval indicates less precision than a narrower interval, but precision is distinct from validity: a precise observational estimate can still be affected by confounding or measurement error. The registry record does not report the estimates or confidence intervals for the outcomes, so neither the direction nor the precision of any comparison can be assessed from it.
Counts and frequencies are also influenced by denominators. The registry lists total enrollment as 171705, but does not report the cohort-specific denominators in the information. The enrollment figure cannot be substituted for those denominators, nor does it show how many people experienced each outcome. The adverse-event information lists zero people at risk in each cohort, so those entries cannot be read as a measured zero event rate among enrolled participants.
What does the sample-size illustration represent?
The registry’s sample-size assumptions describe planning illustrations based on an observed effect, not the study’s original design. The stated assumptions are a two-sided significance level of 0.05, equal allocation between two arms, a normal approximation, and an effect to detect expressed as a fraction of the observed effect. For time-to-event tables, the stated quantity is the total number of events using the Schoenfeld method; for other outcomes, it is participants per arm.
In general, such calculations ask how much information a hypothetical study might need to detect a specified effect under chosen assumptions. They are not observed power and do not establish that the study had that amount of information. The registry record does not report a protocol sample-size justification, and no numerical planning values or observed effect estimates are stated in the registry information available for this analysis. Therefore, the assumptions can be described, but no planning figure or comparison with actual cohort sizes can be interpreted.
What is known about multiplicity and model choices?
The record lists 50 analyses across 7 outcome measures. In general, conducting many analyses creates more opportunities for apparently notable findings to occur by chance, particularly if results are selected for emphasis after analysis. Methods such as prespecifying a primary contrast or adjusting for multiple comparisons can address aspects of this concern, but the registry record does not report whether such procedures were used. It also does not report the statistical models, diagnostics, or sensitivity analyses. No model-specific assumptions, including any approach to over-dispersion, are documented in the registry information. These omissions limit reproducibility and make it difficult to assess how the analysis translated claims counts into effect estimates.
10. Multiplicity, Missing Data and Analysis Populations
The registry identifies 7 outcome measures and 50 analyses. That breadth raises a multiplicity question: when many outcomes or comparisons are examined, some results can appear noteworthy by chance even when there is no underlying association. In general, prespecifying which outcome and comparison are primary, and stating whether multiplicity adjustments will be used, helps readers understand how to interpret a collection of results. The registry record does not report a multiplicity strategy, a hierarchy of analyses, or whether the 50 analyses were prespecified.
The primary endpoint is identified as the number of patients with influenza, and secondary outcomes include asthma, pneumonia, bronchitis, and any respiratory diagnosis. However, the record does not report numerical outcome results, effect estimates, confidence intervals, or an analysis plan describing how comparisons across the four cohorts were handled. It is therefore not possible to assess whether the primary comparison was distinguished from exploratory comparisons or whether any adjustment was applied.
Missing-data handling and analysis populations are also not described in sufficient detail. The registry gives eligibility conditions including age of at least 5 years and at least 6 months of continuous enrollment, but it does not report how many people met each cohort definition, whether anyone was excluded after eligibility assessment, or how missing claims or covariates were treated. It does not state whether analyses followed an intention-to-treat principle, which would not be assumed for this observational design, or describe another named analysis population. The study enrollment field of 171705 does not answer these questions because cohort and outcome denominators are not reported.
In general, missingness can affect an estimate if availability of data is related to exposure or outcome. Without a description of missingness and the analysis population, readers cannot judge that possibility. These details, along with multiplicity procedures, are not reported in the registry record.
11. What the Result Does, and Does Not, Mean
The registry record establishes that a completed post-marketing observational study was designed to examine Relenza prophylaxis in relation to influenza and respiratory outcomes using insurance claims data. It describes the intended population, four cohort categories, the primary influenza outcome, and several secondary respiratory outcomes. It also reports an enrollment figure of 171705 and identifies 7 outcome measures and 50 analyses.
Those design details do not reveal what the data showed. Numerical outcome counts, cohort denominators, estimated contrasts, confidence intervals, and statistical test results are not reported in the registry record. Accordingly, no claim about the direction, magnitude, or precision of an association can be made from the record. A study marked completed is not necessarily a study with interpretable results available in the registry record.
The intended direct, secondary, and total effects are objectives described in the study summary. They should not be read as results or as evidence that causal effects were identified. In general, observational comparisons can be affected by differences between people who receive prophylaxis and those who do not, as well as by how diagnoses and exposure are recorded. The registry explicitly notes that the comparison is not randomized and that the arms are not a like-for-like control comparison. The record does not state an adjustment strategy that would allow readers to assess how these differences were addressed.
The sample-size assumptions are planning illustrations based on an observed effect, not observed power. They cannot establish that the study was adequately powered, particularly because the registry information available does not provide the underlying effect estimate or numerical planning outputs. Likewise, the zero entries in adverse-event fields with zero people at risk do not demonstrate that no adverse events occurred in the enrolled population.
The appropriate interpretation is therefore limited: the registry documents an observational study question and its planned outcome framework, but the outcome findings and their uncertainty are not reported. These details are necessary before drawing conclusions about the observed data.
12. Why This Trial Matters Statistically
This study is statistically instructive because it frames a household-level question using observational claims data. The four cohort descriptions distinguish prophylaxis status from the treatment status of a household index case, reflecting separate questions about the person receiving prophylaxis and other household members. That design makes clear why the comparison is more complex than a simple treated-versus-untreated contrast: household context is part of the study question, and the groups are not randomized.
The record also illustrates the difference between an overall enrollment figure and the information needed to interpret an outcome comparison. Although enrollment is listed as 171705, cohort-specific denominators and outcome counts are not reported. Without them, a reader cannot determine the frequency of influenza in each group or how much information supports a comparison. This distinction is central to reading observational studies, where enrollment alone does not establish the effective sample size for each analysis.
The study has a broad analysis footprint, with 7 outcome measures and 50 analyses. In general, such breadth increases the importance of a clear prespecified analysis plan and transparent multiplicity handling. The registry record does not describe those procedures. It also does not report numerical effect estimates or uncertainty intervals, leaving neither the results nor their precision open to statistical interpretation.
Finally, the registry’s explicit warning that the cohorts are not a like-for-like control comparison is important. Statistical adjustment may help address measured differences in observational data, but it relies on assumptions and cannot, by itself, establish causality. Since the registry record does not detail an adjustment strategy, readers should distinguish the stated aim of estimating effects from evidence that the effects were successfully estimated. The case is a reminder that statistical interpretation depends on the design, denominator, outcome definition, analysis plan, and reporting of results—not merely on a large enrollment figure or a completed status.
13. 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 interpreting the registry record is the absence of numerical outcome results. The record does not report influenza or respiratory outcome counts, cohort denominators, effect estimates, confidence intervals, or test results. It therefore does not support a quantitative account of the association between prophylaxis and the outcomes, or an assessment of precision.
The study is observational, and the registry notes that allocation is not stated and that the arms are not a like-for-like control comparison. This means the cohort contrasts should not be interpreted as randomized treatment effects. The registry record does not report the covariates or methods used for adjustment, if any, or provide information about baseline comparability. The aims refer to direct, secondary, and total effects, but the record does not explain how those quantities were defined analytically or whether they were estimated.
Several measurement and eligibility details are also incomplete. The primary population is described using continuous enrollment in the Normative Health Informatics claims database, but the registry does not report validation of the diagnosis definitions, detailed handling of claims, or complete follow-up procedures. The descriptions of some cohort eligibility criteria are truncated. The study overview describes a 30-day risk period, while the primary-outcome time frame is listed as 2006-2009; the record does not explain the relationship between those periods.
The registry lists 7 outcome measures and 50 analyses but does not report whether the analyses were prespecified or how multiplicity was addressed. Missing-data methods, analysis populations, sensitivity analyses, and model diagnostics are not reported in the registry record. The enrollment of 171705 cannot resolve these gaps, because the number of people in each cohort and analysis is not stated. The adverse-event fields show zero people at risk, which does not permit a meaningful assessment of adverse-event frequency.
14. Related Tutorials
15. Related Statistical Calculators
16. Sources
- ClinicalTrials.gov: Prophylactic Efficacy of Relenza Against Influenza A and B — NCT01156701.
- Registry record last updated 2017-05-30; status last verified 2017-05.
- Results first posted 2011-03-04.
- 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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17. Record Summary
The registry describes a completed post-marketing observational study sponsored by GlaxoSmithKline, with a start date of 2009-07 and primary completion in 2010-05. Its purpose was to assess Relenza prophylaxis in relation to influenza and respiratory outcomes using insurance claims data. The primary outcome is the number of patients with influenza among four cohorts; secondary outcomes include asthma, pneumonia, bronchitis, and any respiratory diagnosis.
The primary population is described as people at least 5 years old with at least 6 months of continuous enrollment in the Normative Health Informatics database during influenza seasons from 2006-2009. The registry lists enrollment of 171705, 7 outcome measures, and 50 analyses. It cautions that this was not a randomized comparison and that the arms are not a like-for-like control comparison.
Numerical outcome results, cohort denominators, effect estimates, confidence intervals, multiplicity procedures, and detailed analysis methods are not reported in the registry record. The study aims and planning assumptions therefore cannot be treated as findings about the observed outcomes.