A Study to Evaluate the Efficacy of MEDI7510 in Older Adults: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for A Study to Evaluate the Efficacy of MEDI7510 in Older Adults (NCT02508194), a randomized phase 2 study. The primary outcome is Percentage of Participants Who Had a First Episode of Acute Respiratory Syncytial Virus-Associated Respiratory Illness (ARA-RI) During Respiratory Syncytial Virus (RSV) Surveillance Period in Season 1.

2. Clinical Question

The endpoint required both specified respiratory or systemic symptoms and laboratory confirmation of RSV. The symptom criteria involved symptoms from at least two of the upper respiratory, lower respiratory, and systemic categories, in specified combinations. RSV confirmation had to come from at least one sample obtained between Day 1 and Day 8 of illness. The surveillance period was approximately 7 months, while Season 1 was approximately 1 year.

The clinical question is therefore narrower than whether participants developed any respiratory illness: it focuses on a first illness episode meeting the symptom definition and confirmed as RSV-related. The registry also describes assessment of antibody responses, influenza vaccine immune responses, and safety, but those outcomes do not replace the primary illness comparison.

3. Trial Design

This was a randomized, triple-masked, parallel-group Phase 2b study sponsored by MedImmune LLC. Its official title describes an evaluation of MEDI7510 for prevention of acute RSV-associated respiratory illness in older adults. The registry lists an enrollment of 1900 and a status of terminated. The reason for termination is not reported in the registry record, and the enrollment figure should not be taken as a count of participants included in the primary endpoint analysis.

The study began on 2015-09-29, with primary completion recorded as 2016-09-09. The interventions were MEDI7510, IIV, and placebo. Participants in the MEDI7510 group received a single intramuscular injection of MEDI7510 in one arm and IIV in the other; the comparator group received placebo matched with MEDI7510 in one arm and IIV in the other. Thus, the randomized contrast concerns adding MEDI7510 rather than placebo while both groups received IIV.

The primary outcome was assessed over the RSV surveillance period in Season 1, beginning Day 14 after dosing and continuing through the end of surveillance, approximately 7 months. The endpoint was a percentage of participants with a first qualifying, laboratory-confirmed ARA-RI episode. The primary analysis population is described as per protocol, based on the as-treated population and follow-up for qualifying symptoms. Part of that population definition is cut off in the registry record.

The registry lists 17 outcome measures and one analysis. It does not report the original sample-size justification, the reasons for selecting the enrollment target, details of allocation concealment, or the full statistical analysis plan. The registry status alone does not establish why the study was terminated or whether termination was related to efficacy, safety, recruitment, or another operational consideration.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Before assignment: A total of 2,044 participants were screened, of which 144 participants were screen failures and 1900 participants were randomized in the study.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Per-protocol population: All participants in the as-treated population (ATP) who were followed for qualifying symptoms for RSV until the end of the RSV surveillance period. Participants who met the primary endpoint criteria and were not followed until the end of the RSV surveillance period were also included in the per-protocol population.

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.

Population: As-treated population (ATP): Participants who received any dose of investigational product (IP). Participants were included in the ATP according to the IP received even if different from that to which the participant was randomized.

6. Primary Endpoint

The registry lists the primary outcome as Percentage of Participants Who Had a First Episode of Acute Respiratory Syncytial Virus-Associated Respiratory Illness (ARA-RI) During Respiratory Syncytial Virus (RSV) Surveillance Period in Season 1, measured over Day 14 after dosing through end of surveillance period (approximately 7 months).

The primary endpoint is the percentage of participants who had a first episode of acute RSV-associated respiratory illness during the RSV surveillance period in Season 1. The observation window began Day 14 after dosing and continued to the end of surveillance, approximately 7 months. It was designed to count a specific clinical event rather than all respiratory symptoms or all laboratory detections of RSV.

For an event to qualify, a participant had to meet specified symptom criteria involving at least two symptom categories: upper respiratory, lower respiratory, and systemic. The record describes the permitted combinations and also requires laboratory confirmation of RSV on at least one sample obtained between Day 1 and Day 8 of illness. Requiring symptoms together with laboratory confirmation makes the endpoint more specific to clinically apparent, RSV-associated illness than a symptom-only measure would be.

A percentage endpoint is useful for comparing the proportion of participants who experience an event over a defined observation period. It can be expressed as a group-specific event percentage and contrasted between randomized groups. General statistical consideration: such a binary outcome does not describe how long an illness lasted, its severity beyond the qualifying criteria, or events outside the specified surveillance window. The primary endpoint therefore answers a focused question about qualifying first episodes during the stated period.

The registry identifies the analysis population as per protocol, but the population description is incomplete. The full rules for follow-up, exclusions, and handling of participants with incomplete observation are not reported in the registry record.

7. Results Posted in the Registry

• MEDI7510 + IIV: 1.7% (16/931) versus 1.6% (15/935) on control; risk difference 0.1 percentage points (95% CI -1.0 to 1.3), risk ratio 1.07 (0.53–2.15); unadjusted two-proportion z-test p = 0.847.

8. Secondary Efficacy Endpoints

The registry also posts results for secondary outcomes. For each outcome below, the endpoint type, the test applied to the posted summary statistics, the result and its interpretation are given in turn. Secondary endpoints are usually not adjusted for multiple testing, so they support rather than confirm the primary finding.

Percentage of Participants Who Had a RSV Polymerase Chain Reaction (PCR)-Positive Respiratory Illness During the RSV Surveillance Period in Season 1

• Endpoint type: Binary: the percentage of participants with the event (counts rebuilt from the posted percentages and group sizes).
• Test: Unadjusted two-proportion z-test, with a Wald 95% confidence interval for the risk difference.
• Result:
  • MEDI7510 + IIV: 1.7% (16/931) versus 1.6% (15/935) on control; risk difference 0.1 percentage points (95% CI -1.0 to 1.3), risk ratio 1.07 (0.53–2.15); unadjusted two-proportion z-test p = 0.847.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between MEDI7510 + IIV and the control. The interval gives the range of effects that remain compatible with the data.

Number of Participants With Any Solicited Symptoms

• Endpoint type: Binary: the number of participants with the event, compared as proportions.
• Test: Unadjusted two-proportion z-test, with a Wald 95% confidence interval for the risk difference.
• Result:
  • MEDI7510 + IIV: 64.1% (606/946) versus 58.9% (558/948) on control; risk difference 5.2 percentage points (95% CI 0.8 to 9.6), risk ratio 1.09 (1.01–1.17); unadjusted two-proportion z-test p = 0.020.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the proportion with the event is statistically higher for MEDI7510 + IIV than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

The registry lists secondary outcomes spanning RSV illness, antibody responses to RSV, influenza antibody responses, and solicited symptoms. These outcomes address different questions: some concern clinical illness, while others assess immune measurements or short-term symptoms after dosing. They should not be treated as interchangeable evidence about the primary clinical endpoint.

Numerical secondary summaries are posted for RSV PCR-positive respiratory illness and for participants with any solicited symptoms. For the other listed secondary outcomes, numerical results are not reported in the registry record. As a result, a complete pattern across the full set of secondary measures cannot be established from the posted results. The primary result remains the main evidence about the prespecified clinical illness question; immune measurements and symptom reporting can provide additional context but do not replace that endpoint.

The secondary outcomes cover multiple measures, groups, and assessment types. General statistical consideration: when many outcomes are examined, some differences may appear notable by chance even if no underlying difference exists. An unadjusted p-value does not account for the number of comparisons. Without a stated multiplicity strategy, an isolated secondary result should carry less weight than a prespecified primary finding and should be interpreted as exploratory rather than as a standalone confirmation.

The registry record does not report a multiplicity adjustment or a hierarchy governing the secondary analyses. It also does not provide a complete numerical account for all listed secondary outcomes. These gaps limit assessment of consistency across outcomes and make it inappropriate to infer a broad clinical pattern from selected results alone.

Secondary outcomes registered for this trial, for reference (only those above were recalculated):

• Percentage of Participants Who Had a RSV Polymerase Chain Reaction (PCR)-Positive Respiratory Illness During the RSV Surveillance Period in Season 1
• Geometric Mean Responses (GMRs) of Serum Antibodies Concentration Against RSV by Anti-Fusion Protein (F) Immunoglobulin G (IgG) Assay
• Geometric Mean Fold Change of Serum Antibodies Concentration Against RSV by Anti-F IgG Assay
• Percentage of Participants Who Had a Post-dose Seroresponse to RSV as Measured by Anti-F IgG Assay
• Geometric Mean Titers (GMTs) of Strain-Specific Hemagglutination Inhibition (HAI) Antibodies to Influenza Antigens Contained in the Seasonal Influenza Vaccine
• Post-dose Geometric Mean Fold Change of Strain-Specific HAI Antibodies to Influenza Antigens Contained in the Seasonal Influenza Vaccine
• Percentage of Participants Who Had a Strain-specific Post-dose Seroresponse to HAI Antibody
• Post-dose GMTs of Serum Antibodies Against RSV by Microneutralization Assay

9. Statistical Interpretation

10. Statistical Methods Explained

The primary outcome is binary at the participant level: each participant either met the qualifying first-episode definition during the surveillance window or did not. The registry presents the outcome as a percentage of participants. For this kind of outcome, a group percentage is calculated from the event count relative to the analysis group size. General explanation: a percentage is intuitive, but comparisons between percentages can be expressed in several ways, and each measure has its own scale and interpretation.

The recalculated comparison uses the risk difference. This is the first group's event proportion minus the comparator group's event proportion, expressed on the probability scale. In this study the reported risk difference is 0.001, with an interval from -0.011 to 0.013. A value of zero represents no difference on this scale. The interval crosses zero, so the estimate is compatible with a range of possible differences on both sides of zero. The risk difference is an unadjusted calculation from the posted summary statistics, not a substitute for a full individual-participant analysis.

The record also gives a risk ratio and an odds ratio for the primary comparison. General explanation: a risk ratio compares the event probability in one group with the event probability in another; an odds ratio compares the corresponding odds. These relative measures can be helpful alongside an absolute difference, but they answer the comparison on different scales. When events are uncommon, the values may appear similar, but they are not interchangeable. No additional interpretation should be inferred from one measure without considering its interval and the event frequency.

The sponsor's result is reported as vaccine efficacy, with a 90% confidence interval. General explanation: vaccine efficacy is a relative measure based on comparing disease occurrence between groups, commonly expressed as a reduction in occurrence. A negative estimate indicates that the observed direction is opposite to a reduction under that measure. The wide interval in this record includes values on both sides of zero, so the sponsor estimate is not precise. The registry does not state the sponsor analysis method in the listed analysis entry.

A confidence interval describes a range of values compatible with the data and the statistical procedure used, under its assumptions. It is not a guarantee that the true value lies in that particular interval, nor is it a range containing a fixed proportion of individual participants. Its width reflects statistical uncertainty. For the primary result, both the recalculated interval and the sponsor interval span values in opposite directions around the no-effect value for their respective measures.

The unadjusted p-value for the recalculated primary comparison is 0.847. General explanation: a p-value measures how unusual data at least as discordant with a specified null hypothesis would be if that hypothesis and the analysis assumptions held. It does not establish that the null is true, quantify the size or clinical importance of an effect, or account automatically for multiple outcomes. The p-value should be considered together with the estimate, its interval, the endpoint definition, and the analysis population.

The trial's primary measure is a percentage, not a count of repeated episodes or an event rate over person-time. Only the first qualifying episode is specified. The endpoint does not quantify illness duration or severity beyond the clinical criteria. The surveillance period is bounded, so illnesses outside that period are not part of this primary measure. General explanation: defining a consistent observation window and event rule helps make the comparison interpretable, while also limiting the question to events captured under that rule.

The analysis population is described as per protocol and based on the as-treated population. Such a population definition is not the same as an intention-to-treat analysis of everyone as randomized. The registry record does not provide a complete eligibility and follow-up definition for this endpoint population, or details of how missing observations and protocol deviations were handled. It also does not report an adjusted primary analysis, stratification factors, or the specific inferential procedure used by the sponsor.

Randomization supports a comparison by assigned group, but the primary endpoint description is tied to a per-protocol population. General explanation: excluding participants or using a population defined after randomization can affect comparability if inclusion depends on post-randomization events. The registry does not supply enough detail to assess whether such concerns arose in this study. The posted group summaries are therefore best read as reported, without assuming a particular missing-data method or adjustment strategy.

11. Confidence Intervals and Precision

Precision concerns how narrowly the data locate an effect estimate. The primary recalculation reports a risk difference of 0.001, with an interval from -0.011 to 0.013. Because the interval crosses zero and reaches in both directions, the data are compatible with a range of possible group differences, not just the point estimate. The interval is an important part of the result: the point estimate alone would conceal this uncertainty.

The sponsor analysis reports vaccine efficacy of -7.1 with a 90% confidence interval from -106.9 to 44.3. This interval is broad and crosses zero for the efficacy measure. It therefore allows values corresponding to different directions of effect, rather than tightly identifying one direction or magnitude. The sponsor result and the recalculated result are on different scales, so their intervals should be interpreted according to their respective measures.

General explanation: confidence intervals reflect sampling variability under the analysis method and its assumptions. They do not account automatically for all sources of uncertainty, including limitations in endpoint ascertainment, missing data, selection of an analysis population, or multiple comparisons. The registry record does not report enough methodological detail to evaluate all of these aspects.

The relatively small number of recorded primary events, as reflected in the posted counts, is relevant to precision: binary outcomes with few events can yield uncertain comparisons even when group sizes are substantial. The registry's enrollment figure is not a substitute for the analysis-specific denominators. Neither a p-value above a conventional threshold nor an interval crossing zero proves there is no effect. The appropriate reading is that the observed estimates are uncertain and do not precisely determine the direction or magnitude of a difference.

12. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The sample-size illustrations are expressed as participants per arm, not as a combined total and not as total events. They are planning calculations based on the observed effect for this outcome, with the target effect reduced to stated fractions of that observed effect. The registry's assumptions for these illustrations are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The original design assumptions for the trial's own enrollment target are not reported in the registry record.

The 80% power column describes the number of participants per arm that the illustration estimates would be needed to detect the specified effect under those assumptions with 80% power. The 90% power column uses a higher probability of detecting that effect if it is present, and therefore requires more participants per arm under the same assumptions. These are planning targets for hypothetical future designs, not descriptions of the number enrolled or analyzed in this study.

The rows for 100%, 75%, and 50% of the observed effect represent progressively smaller effects to be detected. Smaller effects are harder to distinguish from random variation and therefore require more participants. The resulting values can become very large when the observed difference is small. They should be interpreted as illustrations conditional on the chosen assumptions and effect size, not as a recommendation or a claim about what the original investigators planned.

This is not observed power. It does not tell how likely the trial was to detect an effect after the results were known, and it does not resolve the uncertainty in the observed estimate. The registry does not report the trial's own sample-size rationale, any planned interim analyses, or whether the original design assumptions differed from these retrospective illustrations.

13. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, p₀ and p₁ are the control and treatment proportions, and p̄ is their average.

Worked calculation for this trial

1. Control proportion p₀ = 0.016; treatment proportion p₁ = 0.017; average p̄ = 0.017.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.1808 = 0.3543.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.1808 = 0.1521.
4. n = (0.3543 + 0.1521)² / (0.0011)² = 196,298.7, rounded up to 196,299 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
p0 <- 0.0160427807486631                          # control proportion
p1 <- 0.0171858216970999                          # treatment proportion
n_per_arm <- function(power, frac = 1) {
  q1 <- p0 + (p1 - p0) * frac               # smaller effect = fraction of the observed difference
  pbar <- (p0 + q1) / 2
  z_b <- qnorm(power)
  ceiling(round((z_a * sqrt(2 * pbar * (1 - pbar)) + z_b * sqrt(p0 * (1 - p0) + q1 * (1 - q1)))^2 / (q1 - p0)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (unrounded n per arm)
cat("power.prop.test:", round(power.prop.test(p1 = p0, p2 = p1, power = 0.80)$n, 1), "\n")

# Simulation: how often does the z-test reject at the 80%-power sample size?
set.seed(2508194)
n    <- n_per_arm(0.80)
reps <- 20000
x0 <- rbinom(reps, n, p0); x1 <- rbinom(reps, n, p1)
ph <- (x0 + x1) / (2 * n)
z  <- ((x1 - x0) / n) / sqrt(ph * (1 - ph) * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(z) > z_a, na.rm = TRUE), reps))

Output from running the code

100% of observed effect: n per arm = 196,299 (80% power), 262,788 (90% power)
 75% of observed effect: n per arm = 346,026 (80% power), 463,230 (90% power)
 50% of observed effect: n per arm = 771,918 (80% power), 1,033,378 (90% power)
power.prop.test: 196298.7 
Simulated power at n = 196,299 per arm: 0.801 (20000 replicates)

The simulation draws many pairs of event counts at the planned sample size and counts how often the two-proportion z-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

14. Analyses Reported by the Sponsor

The registry's sponsor analysis reports vaccine efficacy of -7.1, with a 90% confidence interval from -106.9 to 44.3. The interval is broad and includes values on both sides of zero, so the sponsor estimate is uncertain. The registry entry does not list a p-value or a specific method for that analysis.

The unadjusted recalculation from the posted group summaries expresses the comparison as a risk difference of 0.001, with an interval from -0.011 to 0.013 and p = 0.847. This calculation is a simple comparison of the reported event summaries. It is not an adjusted reanalysis of individual participant data and does not reproduce any sponsor modeling that may have been used.

Vaccine efficacy and risk difference are distinct measures, so the numeric estimates are not directly interchangeable. Their directions can be understood in relation to the observed group percentages, but the measures retain different scales and potentially different analytic details. The posted group percentages are 1.6% for placebo + IIV and 1.7% for MEDI7510 + IIV; the event counts are 15 and 16, respectively.

The sponsor's analysis remains the registry's reported trial analysis, while the recalculation provides a transparent, unadjusted view derived from the summary data. Neither estimate should be interpreted without its uncertainty, endpoint definition, and stated analysis population. The registry record does not provide sufficient methodological detail to determine whether the sponsor analysis adjusted for covariates or handled missing data in a particular way.

15. Multiplicity, Missing Data and Analysis Populations

The registry lists 17 outcome measures, including the primary endpoint and multiple secondary assessments. These include clinical RSV outcomes, RSV antibody measures, influenza antibody measures, and solicited symptoms. The record does not report a multiplicity adjustment, a hierarchy for testing outcomes, or a statistical plan describing how inferential claims across multiple outcomes were controlled.

General explanation: testing many outcomes increases the chance that at least one result will look unusual under a no-effect assumption. Adjustments or a prespecified testing sequence can help control that risk. Without knowing whether such a strategy was planned or applied, unadjusted secondary p-values should be interpreted cautiously. The primary outcome is the clearest focal test in the registry, but the precise confirmatory status of other outcomes is not reported.

The record describes the primary analysis population as per protocol and based on the as-treated population. The population definition is incomplete, ending after an additional statement about participants who met the endpoint criteria but were not followed to the end of surveillance. The full criteria are therefore not reported in the registry record. The registry does not specify how participants with incomplete surveillance, missing samples, or missing symptom information were handled.

The record does not report whether missing outcomes were imputed, treated as non-events, excluded, or handled using another approach. It also does not provide a detailed intention-to-treat analysis, a sensitivity analysis for missing data, or the full participant flow for the primary endpoint. These omissions prevent a full assessment of how analysis-population choices might affect the result.

Randomization is recorded, but the posted primary result uses a per-protocol population rather than an explicitly described all-randomized analysis. General explanation: the distinction matters because remaining in a per-protocol set can depend on adherence, follow-up, or other post-randomization conditions. The registry does not provide enough information to determine the impact of such selection in this study. The reported estimates should therefore be understood within the population definition that is available, not assumed to represent every randomized participant.

16. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 1% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: myocardial infarction (0.6%), osteoarthritis (0.5%), atrial fibrillation (0.4%), pneumonia (0.3%), invasive ductal breast carcinoma (0.3%).

The registry reports serious adverse events for the safety groups. In the placebo + IIV group, 57 participants were recorded with serious adverse events among 948 at risk; in the MEDI7510 + IIV group, 64 were recorded among 946 at risk. Deaths were recorded for 5 participants in the placebo + IIV group and 3 in the MEDI7510 + IIV group. These are descriptive counts, not evidence by themselves that an intervention caused or prevented an event.

The registry also lists serious adverse event terms with percentages, including myocardial infarction at 0.6%, osteoarthritis at 0.5%, atrial fibrillation at 0.4%, pneumonia at 0.3%, invasive ductal breast carcinoma at 0.3%, and cerebrovascular accident at 0.3%. The listed terms are not a complete safety profile. The record does not provide event-level timing, severity details beyond the serious-event classification, or a causal assessment for these terms.

General statistical consideration: safety counts depend on the population at risk, follow-up, event definitions, and how events are coded. The group counts should be read as observed registry summaries; they do not establish a difference in risk or causation. The registry record does not report enough detail to assess comparative safety statistically.

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

The primary results describe the percentage of participants with a first qualifying, laboratory-confirmed RSV-associated respiratory illness during the stated Season 1 surveillance window. The posted percentages were 1.6% with placebo + IIV and 1.7% with MEDI7510 + IIV. The unadjusted risk-difference estimate is 0.001, and its interval crosses zero. The sponsor's vaccine-efficacy estimate is -7.1, with a 90% interval that is also broad and includes zero.

These findings do not establish a precise difference between the groups. The uncertainty intervals are compatible with effects in more than one direction, and the event counts are limited. A result that does not provide strong evidence of a difference is not proof that the groups are identical. Conversely, the posted point estimates alone do not demonstrate a reliable difference.

The result applies to the endpoint as defined: first episodes meeting specified symptom criteria and laboratory confirmation during the surveillance period. It does not answer whether the groups differed in all respiratory illnesses, illness severity beyond the qualifying criteria, duration, later RSV seasons, or outcomes outside the observation window. It also does not establish the effect of MEDI7510 without IIV, because both groups received IIV.

The analysis population is described as per protocol, and part of its definition is incomplete in the registry record. The registry does not report the full missing-data approach or a complete all-randomized analysis. The study's terminated status is recorded, but its reason is not reported; it should not be used to infer an efficacy or safety conclusion.

The evidence is therefore best read as an uncertain comparison of the posted primary endpoint summaries, accompanied by a sponsor analysis with a wide interval. It should not be extended to claims about other populations, settings, outcomes, or treatment decisions.

18. Why This Trial Matters Statistically

This trial is statistically informative because it illustrates the difference between a point estimate and the uncertainty around it. The primary group percentages are close, and the unadjusted risk-difference interval spans values on both sides of zero. The sponsor's vaccine-efficacy estimate also has a broad interval. Reading the estimates together with their intervals helps avoid treating a single number or a p-value as a complete account of the evidence.

The endpoint definition is another important statistical feature. It combines clinical symptoms with laboratory confirmation, focuses on a first episode, and uses a specified surveillance window. This specificity clarifies what the analysis measures, while limiting conclusions to qualifying RSV-associated illness during that period. The endpoint is not a general measure of all respiratory disease or immune response.

The trial also demonstrates why the analysis population matters. The registry describes a per-protocol population but does not provide the full definition or missing-data methods. A randomized design is valuable, but interpretation still depends on which participants contribute to the primary comparison and how incomplete follow-up is handled.

Finally, the registry includes numerous secondary outcomes across clinical, immunological, and safety domains. Without a reported multiplicity strategy and complete secondary numerical results, those outcomes require cautious interpretation. The record gives enough information to understand the broad clinical question and the reported primary summaries, but not enough to reconstruct every part of the analysis plan or explain the termination. These distinctions are central to evaluating what the trial can and cannot establish.

19. 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.
• Participant counts were reconstructed from posted percentages and arm sizes, so small rounding differences are possible.

Several trial-specific limitations constrain interpretation. The study is marked terminated, but the reason for termination is not reported in the registry record. Without that information, the status cannot be connected to the primary findings or to recruitment, safety, operational, or other considerations.

The primary analysis population is described as per protocol and based on the as-treated population, but the posted definition is incomplete. The record does not provide the full rules for inclusion, the handling of participants with incomplete surveillance, or the method used for missing endpoint data. The registry also does not give a complete all-randomized primary analysis, so the relationship between the reported analysis and all randomized participants cannot be evaluated.

The sponsor analysis method is not specified in the analysis entry. The record does not describe adjustment variables, stratification, interim analyses, or the complete statistical analysis plan. It also does not report the original sample-size justification. The retrospective planning illustration uses stated assumptions, but it should not be mistaken for the study's original design rationale.

Although 17 outcome measures are listed, numerical secondary results are not reported for all of them in the registry record. No multiplicity procedure or testing hierarchy is described. This limits assessment of secondary findings as a coherent family and makes isolated unadjusted comparisons less conclusive.

The primary endpoint is limited to first qualifying episodes during Season 1 and a surveillance window of approximately 7 months beginning Day 14 after dosing. It does not capture every possible RSV outcome or establish effects beyond that period. The record also does not provide enough safety detail to assess event timing or causal relationships. These limitations do not erase the posted observations, but they narrow the conclusions that can be drawn from them.

20. Related Tutorials

21. Related Statistical Calculators

22. Sources

• ClinicalTrials.gov: A Study to Evaluate the Efficacy of MEDI7510 in Older Adults — NCT02508194.
• Registry record last updated 2017-12-26; status last verified 2017-12.
• Results first posted 2017-12-20.
• 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.

23. Record Summary

NCT02508194 is a randomized, triple-masked, parallel Phase 2b study of MEDI7510 with IIV compared with placebo with IIV in older adults. The registry lists enrollment of 1900 and status as terminated. The reason for termination is not reported in the registry record.

The primary endpoint was the percentage with a first qualifying, laboratory-confirmed RSV-associated respiratory illness during the Season 1 surveillance period. Posted percentages were 1.6% for placebo + IIV and 1.7% for MEDI7510 + IIV. The sponsor reported vaccine efficacy of -7.1 with a 90% confidence interval from -106.9 to 44.3; an unadjusted recalculation gives a risk difference of 0.001 with an interval from -0.011 to 0.013.

The estimates are uncertain and do not establish a precise group difference. Interpretation is limited by the incomplete primary population definition, unavailable missing-data and multiplicity details, and incomplete numerical reporting across secondary outcomes.