This page separates reported trial results from statistical interpretation. The ClinicalTrials.gov record contains a posted primary safety endpoint and safety counts, but no formal statistical analyses, effect estimates, confidence intervals, or p-values.
1. Trial at a Glance
MEDLEY was a randomized, parallel, quadruple-masked phase 2/3 trial evaluating MEDI8897 for the prevention of medically attended respiratory syncytial virus lower respiratory tract infection in high-risk children. The trial was completed after enrolling 925.0 participants and posted four outcome measures.
| Feature | MEDLEY |
|---|---|
| Trial name | MEDLEY |
| NCT identifier | NCT03959488 |
| Therapeutic area | Infectious Disease |
| Condition | Respiratory Syncytial Virus Infections |
| Phase | Phase 2/3 |
| Status | COMPLETED |
| Allocation | RANDOMIZED |
| Design model | PARALLEL |
| Masking | QUADRUPLE |
| Primary purpose | PREVENTION |
| Enrollment | 925.0 |
| Arms | 2 |
| Interventions | MEDI8897 (drug); Palivizumab (drug) |
| Lead sponsor | AstraZeneca |
| Sponsor type | INDUSTRY |
| Start | 2019-07-30 |
| Primary completion | 2021-05-03 |
2. Clinical Question
The trial addressed the safety and tolerability of MEDI8897 in a prevention setting involving high-risk children. The registry's brief title describes the broader clinical purpose as prevention of medically attended respiratory syncytial virus lower respiratory tract infection.
Population
High-risk children evaluated for prevention of medically attended respiratory syncytial virus lower respiratory tract infection.
Intervention
MEDI8897, described in the registry data as a drug intervention.
Comparator
Palivizumab, described in the registry data as a drug intervention.
Primary question
What is the safety and tolerability profile of MEDI8897 as assessed through treatment-emergent adverse events, treatment-emergent serious adverse events, adverse events of special interest, and new onset chronic diseases?
3. Trial Design
Random allocation is intended to balance measured and unmeasured characteristics across treatment groups in expectation.
The registry identifies the study as a parallel design with two intervention arms.
The registry identifies the trial as quadruple-masked.
The study's primary purpose is prevention rather than treatment of established disease.
MEDI8897
- Intervention type: drug
- Evaluated for safety and tolerability
- Serious adverse-event count reported in the ClinicalTrials.gov record: 80/614
Palivizumab
- Intervention type: drug
- Used as the comparator intervention in the randomized design
- Serious adverse-event count reported in the ClinicalTrials.gov record: 38/304
4. Primary Endpoint
| Endpoint | Time frame | Registry definition |
|---|---|---|
| Safety and Tolerability of MEDI8897 as Assessed by the Occurrence of All Treatment Emergent Adverse Events (TEAEs) and Treatment Emergent Serious Adverse Events (TESAEs) and Adverse Events of Special Interest (AESIs) and New Onset Chronic Disease (NOCD) | 360 days post first dose | Safety and tolerability of MEDI8897 will be assessed by the occurrence of all treatment-emergent adverse events (TEAEs), treatment-emergent serious adverse events (TESAEs), adverse events of special interest (AESIs), and new onset chronic diseases (NOCDs) |
The registry classifies the primary endpoint type as Other / unclear. The registry-reported endpoint wording therefore matters: this is a safety-and-tolerability endpoint defined through the occurrence of several adverse-event categories rather than a single continuous measurement or a single time-to-event efficacy endpoint.
5. Results
Results are posted on ClinicalTrials.gov, but the ClinicalTrials.gov record contains no formal statistical analyses. That means there is no registry-provided hazard ratio, risk ratio, odds ratio, confidence interval, p-value, treatment-effect estimate, or formal between-group hypothesis test for the primary endpoint in the ClinicalTrials.gov record.
Posted serious adverse-event counts
| Registry safety grouping | Affected / at risk |
|---|---|
| MEDI8897 | 80/614 |
| Palivizumab | 38/304 |
| MEDI8897/MEDI8897 | 23/180 |
| Palivizumab/MEDI8897 | 4/40 |
| Palivizumab/Palivizumab | 2/42 |
These are the serious-adverse-event counts reported in the ClinicalTrials.gov record. The additional group labels involving MEDI8897/MEDI8897, Palivizumab/MEDI8897, and Palivizumab/Palivizumab are reproduced exactly as reported in the registry. The registry extract provided here does not define those labels sufficiently to justify a further interpretation of their treatment sequence or meaning.
The posted safety data establish that serious adverse events were recorded in both the MEDI8897 and palivizumab groups. The affected/at-risk format is useful because it retains the denominator associated with each registry summary.
It does not establish that the treatments differ statistically in serious-adverse-event risk. The ClinicalTrials.gov record contains no formal comparison, confidence interval, or p-value, and therefore no inferential treatment effect should be assigned to these counts.
The denominators also indicate why raw affected counts alone can be misleading: an event count must be interpreted in relation to the number of participants at risk and the definition of the safety analysis population. Because the registry extract does not provide the full statistical analysis dataset or a formal comparison, this page does not calculate a new effect estimate.
6. Secondary and Additional Outcome Results
The trial data state that 4 outcome measures were posted. However, the registry record identifies only the registered primary endpoint in detail and does not provide separate numerical results or statistical analyses for the other posted outcome measures.
7. Statistical Methodology
Because the ClinicalTrials.gov record contains no formal statistical analyses, the statistical discussion below describes how a safety endpoint of this type would ordinarily be analyzed. These are methodological explanations, not claims about analyses actually performed in MEDLEY.
Descriptive safety analysis
For treatment-emergent adverse events and serious adverse events, a basic analysis would summarize the number and proportion of participants experiencing at least one event in each treatment group. Event counts can also be presented by severity, seriousness, system organ class, preferred term, or other prespecified safety categories when those data are available.
For the registry-reported MEDLEY data, the registry reports affected/at-risk counts. This page preserves those counts rather than deriving an unreported inferential analysis from them.
Between-group comparison
If the objective were to formally compare the occurrence of a binary safety event between two randomized groups, several methods could be considered depending on the prespecified analysis plan, event frequency, follow-up structure, and estimand. Examples include a risk difference, risk ratio, odds ratio, or an exact or asymptotic test for a two-group proportion comparison.
The choice of effect measure matters. A risk difference describes an absolute difference in event probability; a risk ratio describes a relative ratio of probabilities; and an odds ratio compares odds rather than probabilities. None should be substituted for another without stating the estimand.
Time-to-event safety analysis
If adverse-event timing were central to the estimand, a time-to-first-event analysis could account for differing follow-up and censoring. Kaplan-Meier methods or regression models could then be considered, depending on the prespecified endpoint definition and assumptions.
However, the registry-reported primary endpoint is explicitly defined through occurrence of adverse-event categories over 360 days post first dose. The registry extract does not state that a time-to-event model was used for this endpoint, so no such analysis is attributed to MEDLEY here.
Safety versus efficacy estimands
Safety analyses answer a different question from efficacy analyses. For efficacy, randomization typically defines the principal comparison population. For safety, exposure to study treatment and time at risk can become especially important because adverse events are causally connected to treatment exposure and observation.
Multiplicity in safety monitoring
A safety endpoint that combines TEAEs, TESAEs, AESIs, and NOCDs potentially involves many individual event categories. If formal inferential testing is performed across numerous safety outcomes, the analysis plan should specify which tests are descriptive and which, if any, are intended for formal inference. The ClinicalTrials.gov record does not report a multiplicity procedure.
8. Statistical Methods Explained
Why is randomization important for a safety comparison?
Randomization creates treatment groups through an allocation mechanism rather than by allowing investigators or participants to choose treatment. In expectation, this reduces systematic differences between groups and supports causal interpretation of differences in outcomes. It does not guarantee identical groups in every measured or unmeasured characteristic.
What does quadruple masking add to the design?
The registry identifies MEDLEY as QUADRUPLE-masked. Masking can reduce the risk that knowledge of treatment assignment changes behavior, assessment, reporting, or other aspects of trial conduct. For adverse events, masking can be relevant because awareness of treatment may influence reporting or clinical interpretation of events.
Why report affected participants and participants at risk?
A count such as 80/614 retains two pieces of information: the number of participants experiencing the specified safety event and the denominator to which that count refers. The denominator provides essential context for interpreting the event count.
Why is a safety endpoint different from a single numerical outcome?
The MEDLEY primary endpoint is a composite safety assessment involving TEAEs, TESAEs, AESIs, and NOCDs. Each category can contain multiple clinically distinct events. A safety analysis therefore often requires a structured hierarchy of descriptive summaries rather than one number intended to capture the entire safety profile.
Why should the registry-reported counts not automatically be converted into a p-value?
A p-value depends on a specified statistical hypothesis, analysis population, estimand, and statistical procedure. Simply having affected/at-risk counts does not reveal which formal comparison was prespecified or whether adjustments were required. Calculating a new p-value from the registry counts could therefore produce an analysis that was not the trial's registered statistical analysis.
What would a confidence interval add?
A confidence interval around a risk difference, risk ratio, odds ratio, or other effect estimate would describe statistical uncertainty around that particular estimate under the chosen model and sampling framework. The registry-reported MEDLEY data contain no such interval for the primary safety endpoint.
9. Safety Results by Reported Group
The ClinicalTrials.gov record contains serious-adverse-event counts for five registry groupings. Because these labels are not further defined in the registry-reported extract, they are presented without assigning additional treatment-sequence meaning to them.
| Reported group | Affected | At risk | Interpretive status |
|---|---|---|---|
| MEDI8897 | 80 | 614 | Registry-provided serious adverse-event count |
| Palivizumab | 38 | 304 | Registry-provided serious adverse-event count |
| MEDI8897/MEDI8897 | 23 | 180 | Registry-provided serious adverse-event count; sequence meaning not defined in registry-reported extract |
| Palivizumab/MEDI8897 | 4 | 40 | Registry-provided serious adverse-event count; sequence meaning not defined in registry-reported extract |
| Palivizumab/Palivizumab | 2 | 42 | Registry-provided serious adverse-event count; sequence meaning not defined in registry-reported extract |
10. Planned Interpretation of the Primary Safety Endpoint
The primary endpoint is explicitly framed around safety and tolerability over 360 days post first dose. For an endpoint of this type, a complete statistical report would ordinarily distinguish at least three layers of information:
Occurrence
How many participants experienced at least one TEAE, TESAE, AESI, or NOCD under the prespecified definitions?
Severity and seriousness
How are events distributed across clinically relevant safety categories, particularly serious adverse events?
Comparative inference
Is there a prespecified estimate of the difference between randomized groups, with an appropriate confidence interval and statistical test?
Time at risk
Are participants followed for comparable periods, and does the analysis account for differential exposure or censoring where necessary?
The registry-reported MEDLEY registry data provide part of the first two layers but do not provide the third. Consequently, the strongest statistical statement supported by the ClinicalTrials.gov record is descriptive rather than inferential.
11. Trial Timeline
Trial start
The registry lists 2019-07-30 as the study start date.
Primary completion
The registry lists 2021-05-03 as the primary completion date.
Trial status
The registry identifies MEDLEY as COMPLETED.
ClinicalTrials.gov results
The ClinicalTrials.gov record indicates that results were posted and that four outcome measures were posted.
12. Limitations
- No formal statistical analyses reported: the trial data contain no formal statistical analyses, so no registry-provided effect estimates, confidence intervals, or p-values are available in the ClinicalTrials.gov recordset.
- Incomplete outcome detail: four outcome measures are reported as posted, but only the primary endpoint is described in the registry record.
- Safety denominator interpretation: the serious-adverse-event summaries have denominators that differ from total enrollment, and the registry-reported extract does not fully define the corresponding analysis populations.
- Unspecified group labels: the meaning of the MEDI8897/MEDI8897, Palivizumab/MEDI8897, and Palivizumab/Palivizumab group labels is not defined in the ClinicalTrials.gov record.
- No inferential safety comparison: affected/at-risk counts alone do not establish whether a between-group difference is statistically significant or clinically meaningful.
- Safety endpoint breadth: TEAEs, TESAEs, AESIs, and NOCDs represent distinct safety concepts, so a single overall summary can conceal important differences among event categories.
- Time frame: the registered primary endpoint uses 360 days post first dose, so analyses using other observation periods would represent different estimands unless explicitly harmonized.
- Registry-versus-publication distinction: the ClinicalTrials.gov record identifies a linked publication by PMID but do not supply numerical statistical analyses from that publication. This page therefore does not import additional results from it.
13. Why This Trial Matters Statistically
MEDLEY is useful as a teaching case because it illustrates an important feature of clinical-trial statistics: a randomized design can support strong causal comparisons, but the quality of the statistical conclusion still depends on the endpoint definition, analysis population, denominator, follow-up period, and prespecified inferential method.
| Concept | How it appears in MEDLEY |
|---|---|
| Randomization | The registry identifies the allocation as RANDOMIZED. |
| Parallel design | The registry identifies the design model as PARALLEL. |
| Quadruple masking | The registry identifies the masking as QUADRUPLE. |
| Prevention trial | The primary purpose is PREVENTION. |
| Safety endpoint | The primary endpoint evaluates safety and tolerability through TEAEs, TESAEs, AESIs, and NOCDs. |
| Fixed follow-up frame | The registered primary endpoint uses 360 days post first dose. |
| Denominator-based interpretation | Serious adverse events are reported as affected/at-risk counts. |
| Analysis transparency | The ClinicalTrials.gov record contains posted results but no formal statistical analyses. |
| Analysis-population awareness | Enrollment of 925.0 should not automatically be substituted for the denominators used in safety summaries. |
| Randomization versus inference | Randomization supports comparison, but a formal statistical conclusion still requires a prespecified analysis. |
14. What the Posted Safety Counts Do — and Do Not — Mean
The reported 80/614 and 38/304 values indicate that serious adverse events were observed among participants represented by those respective MEDI8897 and palivizumab safety summaries.
They do not by themselves establish a relative treatment effect, an absolute treatment effect, or statistical significance. Those conclusions require a defined estimand and a specified comparison procedure.
An affected count without its denominator cannot describe the frequency of an event. Even with a denominator, interpretation depends on how participants entered the safety population and how follow-up was handled.
The ClinicalTrials.gov record contains no formal statistical analyses. A p-value calculated independently from the posted counts would answer a newly constructed statistical question rather than necessarily reproducing the trial's prespecified analysis.
The registered endpoint specifies 360 days post first dose. Safety interpretation therefore depends not only on whether an event occurred but also on the observation window defining the endpoint.
15. Clinical Interpretation vs Statistical Interpretation
Statistical interpretation
The trial is randomized and quadruple-masked, and the registry provides serious-adverse-event counts for specified groups. The ClinicalTrials.gov record does not provide formal statistical comparisons for those counts.
Clinical interpretation
The available information describes safety and tolerability using adverse-event categories and serious-adverse-event counts. A complete clinical safety interpretation would require the detailed event-level or category-level results that are not included in the ClinicalTrials.gov record.
16. Planned Statistical Analysis Framework
| Analysis component | Typical role for this endpoint | Status in reported MEDLEY data |
|---|---|---|
| TEAE incidence | Descriptive safety summary of participants experiencing treatment-emergent adverse events | Endpoint defined, numerical detail not reported |
| TESAE incidence | Descriptive serious-adverse-event summary and, if prespecified, between-group comparison | Some affected/at-risk counts reported; no formal comparison reported |
| AESI incidence | Focused analysis of prespecified adverse events of special interest | Endpoint defined; numerical detail not reported |
| NOCD incidence | Assessment of new onset chronic diseases | Endpoint defined; numerical detail not reported |
| Confidence intervals | Quantification of uncertainty around an effect estimate | Not reported |
| P-values | Formal test of a prespecified null hypothesis | Not reported |
| Adjustment for multiplicity | Control of type I error when multiple formal hypotheses are tested | Not reported |
17. Key Statistical Takeaways
Randomization creates the comparison
The randomized allocation is the foundation for comparing the MEDI8897 and palivizumab groups while limiting systematic allocation bias.
Masking protects measurement
Quadruple masking is a design feature intended to reduce the influence of treatment knowledge on trial conduct and outcome assessment.
Safety requires denominators
The registry-reported serious-adverse-event results appropriately retain affected and at-risk counts rather than presenting event counts alone.
Descriptive is not inferential
Posted safety counts describe observed events, but without a formal analysis they do not establish a statistically significant treatment difference.
18. Related Tutorials
Learn more about the methods used in this trial:
19. Related Statistical Calculators
20. Sources
- ClinicalTrials.gov: MEDLEY, NCT03959488.
- Linked publication: PubMed record for PMID 35235733: 35235733. The ClinicalTrials.gov record identifies this publication but do not provide its numerical statistical analyses, so no additional publication results are incorporated into this page.
Continue through the Clinical Biostats library
Explore clinical-trial methods through tutorials and statistical calculators that explain randomization, masking, safety endpoints, and comparative analysis.
21. Record Summary
MEDLEY is a completed randomized, parallel, quadruple-masked phase 2/3 prevention trial with 925.0 enrolled participants and two interventions: MEDI8897 and palivizumab. Its registered primary endpoint evaluates the safety and tolerability of MEDI8897 through the occurrence of TEAEs, TESAEs, AESIs, and NOCDs over 360 days post first dose. The ClinicalTrials.gov record reports serious-adverse-event counts, including 80/614 for MEDI8897 and 38/304 for palivizumab, along with three additional registry groupings. Because no formal statistical analyses were posted, these observations remain descriptive: no formal treatment-effect estimate, confidence interval, or p-value is attributed to the trial here.