Durability and Impact of the Seasonal Influenza Vaccine on H5 Induced B Cell Response: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Durability and Impact of the Seasonal Influenza Vaccine on H5 Induced B Cell Response (NCT03701061), a non-randomized phase 4 study. The primary outcome is Number of Participants With a Four-fold Increase in Stem-specific Antibody Titers (H5, Hemagglutinin Antibody) Against H5N1 at Day 29 After Vaccination With the Seasonal Influenza Vaccine Among All the Participants in Both Arms.

2. Clinical Question

The study asks whether prior AS03 adjuvant status is associated with a difference in the antibody response observed after seasonal influenza vaccination. It is an exploratory question about immune responses, not a randomized test of seasonal influenza vaccine against no vaccination. There is no untreated comparison group described in the registry record.

The endpoint compares antibody titers measured at baseline before study vaccination with titers measured on Day 29. The registry record does not report the number of participants who met the four-fold increase criterion, nor does it report an estimated difference between the two groups. As a result, the clinical question is identifiable from the stated objective and endpoint, but the posted record does not show the primary outcome needed to answer it.

3. Trial Design

This was a prospective, single-site exploratory study sponsored by Emory University. The registry lists it as Phase 4, with non-randomized allocation, a parallel model, and no masking. The study is marked completed. Its recorded start date is 2018-10-11, and its primary completion date is 2019-02-28. The registry lists enrollment of 12.

The two groups were defined by participation in earlier H5N1 vaccine studies: one group had received H5N1 vaccine with AS03 adjuvant, and the other had received it without AS03. Participants in both groups were to receive a single dose of the FDA-approved 2018-2019 seasonal influenza vaccine, Fluarix Quadrivalent. The listed interventions use the same seasonal influenza vaccine name in each group. Thus, the contrast is based on prior adjuvant exposure, rather than assignment to seasonal vaccine versus a control intervention.

Because allocation was not randomized, the groups should not be treated as if they were interchangeable apart from AS03 history. Differences between them could reflect their earlier study participation or other characteristics; the registry record does not report enough information to assess such differences or to describe adjustment for them. The record also does not report the method used to recruit or select participants from the earlier studies.

The study’s main purpose was to examine immune responses to H5N1 vaccine previously received with or without AS03 after seasonal influenza vaccination. Secondary outcomes address adverse events after the seasonal vaccine, including solicited events, unsolicited events, and serious adverse events. The registry record does not report the protocol’s sample-size justification, masking procedures beyond the listed absence of masking, or any detailed statistical analysis plan.

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

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

6. Primary Endpoint

The registry lists the primary outcome as Number of Participants With a Four-fold Increase in Stem-specific Antibody Titers (H5, Hemagglutinin Antibody) Against H5N1 at Day 29 After Vaccination With the Seasonal Influenza Vaccine Among All the Participants in Both Arms, measured over Baseline (Day 1) before vaccination and Day 29 post vaccination.

The primary endpoint is the number of participants with a four-fold increase in stem-specific antibody titers against H5N1 at Day 29 after seasonal influenza vaccination. The antibody measure is described as a hemagglutinin inhibition antibody titer. Blood was drawn at baseline before study vaccination and again on Day 29, and participants meeting the four-fold increase criterion were to be recorded.

This endpoint converts a change in a continuous laboratory measurement into a participant count: each participant either meets the stated increase criterion or does not. Such a response definition can make the outcome easier to interpret as the proportion or number of people meeting a prespecified immune-response threshold, rather than as a change in the average titer alone. That is a general feature of responder endpoints; it does not establish that the threshold predicts a clinical outcome.

The primary outcome is relevant to the stated research question because the study concerns H5-specific immune response after seasonal influenza vaccination, with groups separated by prior AS03 exposure. However, the registry record does not report the endpoint count in either group, the total number assessed for the endpoint, or an estimate of the contrast. It therefore does not show how many participants met the response definition or how precisely any difference between groups was estimated.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary endpoint is a count of participants who satisfy a binary response definition: a four-fold increase in H5 stem-specific antibody titer between baseline and Day 29. General statistical explanation: a binary endpoint records whether each participant meets a criterion, while a group-level summary can report the number or proportion meeting it. To compare groups, an analysis would ordinarily quantify the response in each group and estimate a contrast, with uncertainty. The registry record does not report those outcome summaries or an analysis result.

What does a confidence interval communicate?

General statistical explanation: a confidence interval describes uncertainty around an estimated quantity under the assumptions of the statistical method used. A narrow interval indicates greater precision than a wide interval, while an interval that includes values consistent with little or no difference may leave the size and direction of a group contrast uncertain. These interpretations depend on the analysis and its assumptions. No confidence interval for the primary endpoint is reported in the registry record, so its precision cannot be assessed.

Why does the non-randomized design matter?

Random assignment can, on average, balance both measured and unmeasured participant characteristics between groups. Here, allocation is listed as non-randomized, and group membership follows prior receipt of H5N1 vaccine with or without AS03. General statistical explanation: when groups are formed this way, pre-existing differences may be associated with both group membership and the outcome. A crude contrast can therefore combine an association with prior adjuvant status and other group differences. The registry record does not report a covariate-adjusted primary analysis or sufficient baseline information to assess comparability.

The parallel structure means the two groups are considered alongside one another, rather than as a crossover comparison in which each participant receives both study conditions. The groups differ by prior AS03 exposure, while both are described as receiving the seasonal influenza vaccine. This design does not isolate the effect of seasonal influenza vaccine versus no seasonal vaccination, because no such control group is described.

How should the response threshold be understood?

A responder definition can simplify interpretation by classifying participants according to whether their titer change crosses a stated threshold. General statistical explanation: converting a continuous measurement into a binary outcome can discard information about the size of changes within each category. Participants just below and well below the criterion are grouped together, as are participants with different increases that all meet it. The registry record defines the four-fold criterion but does not report continuous titer summaries or the number who met the criterion.

The primary endpoint timeframe compares baseline before vaccination with Day 29 after vaccination. The record names hemagglutinin inhibition antibody titers and blood draws at those time points. It does not describe the laboratory assay’s detailed procedures, quality-control approach, handling of measurements outside assay limits, or the statistical treatment of missing or unusable samples. Those details are not reported in the registry record.

What can be inferred from the posted safety counts?

The adverse-event summary lists counts for serious events, other events, and deaths by group. General statistical explanation: a count without event detail, a defined observation window, or a fuller description of ascertainment does not by itself characterize severity patterns or establish causation. The summary reports no serious adverse events and no deaths in either group, and one other adverse event among participants who received AS03. The event’s description and attribution are not reported in the registry record. The separately listed secondary outcomes specify solicited events at Day 8, unsolicited events at Day 29, and serious adverse events at Day 365, but the group summary fields do not attach those timeframes to the individual counts.

The sample-size assumptions describe a planning illustration based on the observed effect, with a two-sided significance level of 0.05, equal allocation, and a normal approximation; the target effect is a stated fraction of the observed effect. Such calculations are planning illustrations, not observed power and not evidence that an effect was detected. The record does not report the resulting planning counts, the trial’s own sample-size justification, or whether a calculation informed enrollment. Since the primary effect estimate is not reported, the posted record also does not permit an independent assessment of planning assumptions against the observed primary outcome.

Finally, the record lists zero analyses. It does not report the statistical test or model used for the primary outcome, any adjustment for group differences, a prespecified analysis population, or a strategy for controlling false-positive findings across multiple outcomes. Those analysis details are not reported in the registry record, so no unreported method should be assumed.

10. Exact Estimates for Each Arm

No two-arm comparison is shown for this trial, but each arm's result can still be summarized with exact interval estimates computed from the posted counts. The Clopper-Pearson interval is exact and conservative; the Wilson interval is a common closer-to-nominal alternative; the Bayesian credible interval uses a uniform Beta(1, 1) prior. For small groups the three can differ noticeably.

R code and output

arm    <- c("Participants That Received AS03 Adjuvant", "Participants That Did Not Receive AS03 Adjuvant")
n      <- c(9, 3)
events <- c(0, 0)
for (i in seq_along(n)) {
  ci <- binom.test(events[i], n[i])$conf.int          # Clopper-Pearson exact interval
  cr <- qbeta(c(0.025, 0.975), 1 + events[i], 1 + n[i] - events[i])   # Bayesian, uniform Beta(1,1) prior
  wi <- (function(x, n) { p <- x / n; z <- qnorm(0.975); d <- 1 + z^2 / n
    c((p + z^2 / (2 * n) - z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d, (p + z^2 / (2 * n) + z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d) })(events[i], n[i])
  cat(sprintf("ARM|%s|%d|%d|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f\n", arm[i], n[i], events[i], 100 * events[i] / n[i],
              100 * ci[1], 100 * ci[2], 100 * wi[1], 100 * wi[2], 100 * cr[1], 100 * cr[2]))
}

ARM  Participants That Received AS03 Adjuvant  9  0  0.0  0.0  33.6  -0.0  29.9  0.3  30.8
ARM  Participants That Did Not Receive AS03 Adjuvant  3  0  0.0  0.0  70.8  0.0  56.1  0.6  60.2

11. Multiplicity, Missing Data and Analysis Populations

The registry record lists one primary outcome and three secondary safety outcomes. The primary outcome is the number of participants with a four-fold increase in H5 stem-specific antibody titers at Day 29. The secondary outcomes concern solicited Grade 2 and above adverse events at Day 8, unsolicited Grade 2 and above adverse events at Day 29, and serious adverse events at Day 365.

When a study examines multiple outcomes, general statistical practice may account for the possibility that testing many hypotheses increases the chance of at least one apparently unusual result. The registry record does not report a multiplicity strategy, a hierarchy among secondary outcomes, or whether any outcome was treated as exploratory for statistical testing. It is therefore not possible to determine how multiple comparisons were handled.

The record also does not report how missing baseline or Day 29 antibody measurements were handled, whether any participants were excluded from the primary endpoint analysis, or how incomplete adverse-event follow-up was treated. The analysis populations are not reported in the registry record. Although the record lists enrollment of 12 and adverse-event risk groups of 9 and 3, those counts do not establish how many participants had evaluable antibody measurements or were included in each endpoint analysis.

No primary analysis result or analysis methods are posted; the record lists zero analyses. Consequently, there is no reported basis for assessing missing-data assumptions, sensitivity analyses, or the effect of any participant exclusions on the immune-response estimate. These are uncertainties about reporting, not evidence that data were missing or that participants were excluded.

12. 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 0% reporting threshold.

Most frequent non-serious adverse event terms

The adverse-event summary lists no serious adverse events among participants who received AS03 adjuvant, with 9 at risk, and none among participants who did not receive AS03 adjuvant, with 3 at risk. It also lists no deaths in either group. For other adverse events, the summary records 1 event in the AS03 group and 0 in the group without AS03, using the same risk-group counts.

These are counts, not a complete description of event type, severity, timing, or relatedness to vaccination. The record does not describe the one other event. It also does not report whether the adverse-event summary counts correspond to the separately specified secondary outcome timeframes: solicited Grade 2 and above events at Day 8, unsolicited Grade 2 and above events at Day 29, and serious adverse events at Day 365.

General statistical explanation: zero observed events in a small group does not establish that the underlying event risk is zero. The group sizes are unequal, and the summary does not provide uncertainty intervals or detailed ascertainment information. These figures describe what the registry record reports; they do not by themselves establish whether an event was caused by vaccination.

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

The record identifies an exploratory study of immune responses after seasonal influenza vaccination among participants with different prior H5N1 vaccine adjuvant histories. Its primary question concerns the count of participants whose H5 stem-specific antibody titers increased four-fold by Day 29. Both groups were to receive the same seasonal vaccine, so the intended comparison is between prior AS03 exposure groups rather than between vaccination and no vaccination.

The record does not report the primary endpoint counts or an estimated group contrast. It therefore does not show whether either group had more participants meeting the response definition, how large any difference was, or how precisely it was estimated. It also does not support a conclusion about clinical protection or any other clinical outcome: the stated primary endpoint is an antibody response, and clinical outcomes demonstrating benefit are not reported.

Any observed difference in a non-randomized comparison would need cautious interpretation because group membership reflects prior study participation and adjuvant history. Without reported baseline characteristics and analysis details, the extent to which groups were comparable cannot be assessed. The small and unequal adverse-event group counts also limit what can be learned from the safety summary alone.

The absence of a posted primary result should not be read as evidence that there was no response or no difference. It means the registry record does not contain the result needed to assess those possibilities. The record does report no serious adverse events and no deaths in either group, alongside one other adverse event in the AS03 group and none in the group without AS03. Those counts are descriptive and do not establish causality or the complete safety profile.

In short, the record documents the study question, design, endpoint definition, and limited adverse-event counts. It does not provide the primary immune-response result or sufficient statistical detail to quantify the comparison.

14. Why This Trial Matters Statistically

This trial is statistically instructive because its central comparison is defined by prior treatment history rather than randomized assignment within the study. Participants with and without prior AS03 exposure both received the seasonal influenza vaccine. That structure makes clear why the group contrast is not automatically a causal estimate of the effect of AS03: groups may differ for reasons other than the exposure used to label them.

The endpoint also illustrates the distinction between a laboratory measurement and a responder count. The stated outcome classifies participants according to whether their antibody titer increased four-fold. Such thresholds can provide a simple interpretation, but they do not retain all information about the size of each participant’s change. The registry record does not report either the responder counts or continuous antibody results.

The record includes an enrollment of 12 and adverse-event groups of 9 and 3. This highlights why denominator and uncertainty information matter, especially in an unequal, small-group comparison. A count alone cannot indicate how stable an estimate is, and zero events in a group should not be interpreted as proof that an event cannot occur.

Finally, the registry record separates a clearly stated endpoint from the results needed to evaluate it. Without primary counts, an effect estimate, or an uncertainty interval, the research question cannot be answered from the posted record. This distinction is important when reading clinical trial registrations: a defined outcome and a completed study do not themselves constitute a reported outcome analysis.

15. 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 of the posted record is that it does not report the primary endpoint result. There are no group-specific counts for four-fold antibody increases, no estimated contrast, and no confidence interval or test result. The record lists zero analyses, so the statistical evidence for the primary question cannot be evaluated.

The design is non-randomized. Participants were grouped according to participation in earlier H5N1 vaccine studies with or without AS03, and the registry record does not report baseline characteristics that would allow assessment of group comparability. It does not report an adjusted analysis to address potential group differences. Thus, even if a primary contrast were available, causal interpretation would require caution.

The record lists enrollment of 12, while adverse-event summary groups contain 9 and 3 participants at risk. It does not report the number with evaluable primary endpoint data, the analysis populations, or whether all enrolled participants completed the Day 29 assessment. Missing-data handling and reasons for any unavailable measurements are not reported in the registry record.

The study is described as exploratory and single site. The record does not report a sample-size justification or the statistical methods used for the primary analysis. It also does not report a multiplicity plan, detailed assay methods, or the event description for the one other adverse event. Although adverse-event outcomes include specified follow-up timeframes, those timeframes are not attached to the grouped summary counts. These reporting gaps limit interpretation of both efficacy-related immune outcomes and safety counts.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Durability and Impact of the Seasonal Influenza Vaccine on H5 Induced B Cell Response — NCT03701061.
• Registry record last updated 2020-03-11; status last verified 2020-02.
• Results first posted 2020-03-11.
• 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.

19. Record Summary

NCT03701061 is a completed, prospective, single-site exploratory study sponsored by Emory University and listed as Phase 4. It used non-randomized allocation, a parallel model, and no masking. The registry lists enrollment of 12, a start date of 2018-10-11, and a primary completion date of 2019-02-28.

The study compared participants with prior H5N1 vaccine exposure with and without AS03 adjuvant; both groups were to receive a single dose of the 2018-2019 seasonal influenza vaccine, Fluarix Quadrivalent. The primary endpoint was the number with a four-fold increase in H5 stem-specific antibody titers at Day 29. That primary result and its statistical analysis are not reported in the registry record.

The adverse-event summary lists no serious adverse events or deaths in either group, and one other adverse event in the group that received AS03 versus none in the group that did not. The record does not provide further detail about that event.