Immune Responses to H5N1 Vaccine With and Without AS03 Adjuvant: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Immune Responses to H5N1 Vaccine With and Without AS03 Adjuvant (NCT01578317), a randomized phase 1, phase 2 study. The primary outcome is Flu Antibody Titers.

2. Clinical Question

3. Trial Design

This was a randomized, quadruple-masked, parallel-group Phase 1/Phase 2 study. Participants were assigned to H5N1 vaccine with AS03 or to H5N1 vaccine without adjuvant. The registry record describes both groups receiving an initial vaccination on day 1 and a booster on day 21. The trial is listed as completed, with enrollment of 43 participants.

The study focused on healthy volunteers between 18 and 45 years of age. The registry description says participants were screened with a physical examination and medical history. It also describes inpatient stays around vaccination, frequent blood draws, and monitoring for signs or symptoms that might be caused by vaccination. Additional blood samples were planned after the initial vaccination.

Random allocation is intended to make treatment groups comparable, on average, with respect to factors that could affect outcomes. Masking can reduce the influence of expectations on participant reports, clinical care, and outcome assessment. The registry record does not report how the random sequence was generated, which roles were masked, or how allocation was concealed.

The study's primary outcome was antibody titer against five H5N1 virus strains, assessed at days 0, 21, 42, and 100. The record defines the measurements but does not report the numerical titers or an analysis comparing the groups. The trial began on 2012-03-20 and reached primary completion on 2016-01-31.

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 Flu Antibody Titers, measured over Days 0, 21, 42, and 100.

The primary endpoint concerns antibody-neutralization titers measured by microneutralization. The assay assessed serum activity against A/Vietnam/1194/2004 (clade 1), A/Indonesia/5/2005 (clade 2.1), A/Turkey/15/2006 (clade 2.2), A/Egypt/3072/2010 (clade 2.2), and A/Anhui/1/2005 (clade 2.3.4). Measurements were specified at days 0, 21, 42, and 100. Day 0 is the prevaccination measurement; the later measurements track antibody titers after vaccination and the booster.

Neutralization titers are a laboratory measure of antibody activity against a virus strain. They provide a way to describe an immune response, but a laboratory endpoint alone does not establish a clinical benefit. The registry record describes geometric mean titers as the outcome measure and standard deviation as the dispersion measure. It also states that sera were tested at an initial dilution of 1:20 and that negative results (<1:20) were assigned a titer of 10.

The listed time points and multiple virus strains make the endpoint multidimensional. A complete interpretation would require the actual titers, measures of uncertainty, and a clear account of which comparisons were intended. Numerical antibody results and inferential analyses are not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry describes an outcome based on geometric mean antibody titers, with standard deviation recorded as the dispersion measure. These summaries answer different questions. A geometric mean is a way to summarize measurements that are analyzed on a logarithmic scale and then expressed on the original scale. It can be useful for titers, which may vary multiplicatively rather than by equal additive steps. The standard deviation describes spread in the measurements, but its interpretation depends on the scale used. The registry record does not give the numerical estimates or further details about the calculation.

What does a neutralization titer represent?

In general, a neutralization assay tests whether antibodies in serum inhibit a virus under laboratory conditions. A titer is a summary of the dilution at which activity is measured. Higher titers can indicate greater measured neutralizing activity in that assay, but assay results are not the same as a clinical outcome. Their meaning depends on the assay procedures, the virus strain tested, and how results are summarized. The registry record names the microneutralization assay and the five strains, but detailed assay validation and laboratory procedures are not reported in the registry record.

Why does the lower measurement limit matter?

The record states that sera were initially tested at a dilution of 1:20 and that negative results, described as <1:20, were assigned a titer of 10. This is a rule for handling measurements below the assay's initial dilution threshold. In general, assigning a value to results below a detection limit allows them to be included in summaries, but it also means the assigned value is not a direct measurement of the true titer. The choice can affect calculated summaries, especially when many observations are below the limit. The number of such observations is not reported in the registry record.

Why are measurements at several times and against several strains different analyses?

Each strain-specific measurement represents a different antibody response, and each time point represents a different stage of follow-up. In general, examining multiple outcomes creates a multiplicity issue: when many comparisons are tested, the chance of finding at least one apparently unusual result by chance can increase. Researchers may address this through a prespecified primary comparison, adjusted significance thresholds, hierarchical testing, or an explicitly exploratory interpretation. Which strategy was planned or used is not reported in the registry record. The posted record notes that the outcome has several categories or time points and is not reduced to one comparison.

Repeated measurements from the same participant are related. In general, an analysis that accounts for this within-participant correlation can use the data differently from an analysis that treats each measurement as independent. The analysis model, handling of correlation, and any covariate adjustment are not reported in the registry record. No estimate or test result is posted to assess how these choices affected the comparison.

How should uncertainty be assessed?

In general, an estimate describes the observed contrast, while a confidence interval conveys its precision under the chosen model. A p-value, when used, describes how compatible the data are with a specified null hypothesis under the analysis assumptions; it does not measure the probability that a treatment works. Neither a confidence interval nor a p-value can be reconstructed from the outcome description alone. The registry record reports no numerical antibody results, confidence intervals, or hypothesis tests.

The registry's sample-size assumptions describe a planning illustration based on an observed effect, with a two-sided significance level of 0.05, equal allocation, and a normal approximation. The illustration is not the trial's own design justification, and its values are not reported in the registry record. Sample-size calculations are planning tools: they describe requirements under stated assumptions and are not evidence that an observed effect is precise. They must not be interpreted as observed power.

Finally, a complete statistical interpretation depends on how participants are included in analyses and how missing measurements are handled. The analysis population, amount and pattern of missing antibody data, imputation approach, and sensitivity analyses are not reported in the registry record. These omissions prevent evaluation of whether the available outcome data represent all randomized participants and whether conclusions are robust to missingness.

10. Multiplicity, Missing Data and Analysis Populations

The endpoint contains measurements at days 0, 21, 42, and 100, and evaluates five H5N1 virus strains. This creates multiple possible contrasts across time, strain, and treatment group. In general, testing many contrasts without a prespecified strategy can make isolated findings harder to interpret because chance variation may produce apparently notable results. A multiplicity plan might identify a primary contrast or specify how statistical evidence is adjusted or interpreted across comparisons. The multiplicity strategy is not reported in the registry record.

The record indicates that the primary outcome has several categories or time points and was not reduced to one comparison. It lists no analyses. Numerical antibody results, group contrasts, confidence intervals, and hypothesis tests are not reported in the registry record. The statistical analysis plan, including any interim analyses, is not reported in the registry record.

Missing outcome data can affect estimates when measurements are absent, particularly if absence is related to participants' responses or other factors. In general, methods may range from analyzing available observations to using an imputation model or sensitivity analyses, with different assumptions. The amount and pattern of missing antibody data, the method used to address missingness, and sensitivity analyses are not reported in the registry record.

The analysis populations are also not reported in the registry record. It is therefore unclear from the record whether analyses were intended to include all randomized participants, participants who received vaccinations, or participants with available measurements under another definition. The randomization and masking labels do not, by themselves, resolve these questions about analysis conduct.

11. 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 5% reporting threshold.

Most frequent non-serious adverse event terms

The registry safety entries list 22 participants at risk in the AS03-adjuvanted group and 20 in the unadjuvanted group. Serious adverse events are recorded for 0 participants in each group, and deaths are recorded as 0 in each group. The entries for other adverse events list 17 participants in the AS03-adjuvanted group and 13 in the unadjuvanted group.

These figures are counts as recorded in the registry, not percentages or adjusted comparisons. They do not by themselves show whether event frequency differed between groups, and they do not establish that an event was caused by vaccination. The record does not report the definition of serious adverse events, the specific terms for other adverse events, their severity, or their timing. It lists no top serious-event terms.

Absence of recorded serious events in these entries should be read narrowly: it describes the registry counts for this study, not the possibility of rare events or events that might be detected in a different population or setting. The safety entries are distinct from the primary antibody endpoint and cannot fill the gap left by the unreported antibody results.

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

This trial is designed to compare immune responses to H5N1 vaccine with and without AS03 adjuvant in healthy volunteers. The registry record identifies randomization, masking, the vaccination schedule, the antibody assay, the virus strains, and the measurement times. It also reports safety counts. Those details describe the question and conduct of the study, but they do not provide a numerical answer to the primary antibody comparison.

The record does not report antibody titers, group differences, confidence intervals, p-values, or an inferential analysis. It is therefore not possible to determine from the posted results whether the groups differed, how large any difference was, or how precisely it was estimated. The lack of a reported result should not be interpreted as evidence of equal responses or as evidence of a particular response in either group.

Even if numerical antibody results were available, laboratory neutralization titers would remain an immune-response measure rather than a direct measure of clinical outcomes. The trial's endpoint can describe assay-measured antibody activity against specified strains, but the registry record does not establish how that activity relates to protection or to outcomes outside the study.

The reported safety counts provide a limited description of recorded events in this study. They do not establish causation, exclude uncommon events, or replace a full account of event type, severity, and follow-up. Overall, the registry supports understanding what was studied and how the primary outcome was defined, while leaving the principal comparative result and its uncertainty not reported in the registry record.

13. Why This Trial Matters Statistically

This trial is statistically notable because its primary outcome is not a single measurement at a single time. It tracks antibody-neutralization titers over follow-up and across several virus strains. That structure raises practical questions about which comparisons matter most, how repeated observations are modeled, and how evidence across multiple strains and times should be interpreted.

The design also pairs a randomized, masked comparison with a laboratory immune-response endpoint. Randomization can support comparison between groups, while masking can limit some sources of bias. Those design features are useful context, but they do not replace reporting the numerical estimates and their uncertainty. Without those results, readers cannot assess the magnitude or precision of the antibody contrast.

Measurement limits are another important statistical feature. The record assigns a titer of 10 to results below <1:20. In general, rules for values below an assay threshold influence summaries and should be understood alongside the number of affected observations and any sensitivity analyses. Those details are not reported in the registry record.

The registry also illustrates why a defined endpoint and a completed study are not the same as a fully interpretable result. The record describes what investigators intended to measure and reports safety counts, yet it does not provide the antibody estimates or analysis needed to answer the primary comparative question. For statistical readers, that distinction is central: design information explains how a result might be interpreted, while the result and its uncertainty are needed to quantify what the data show.

14. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

The main limitation for interpreting this trial from the registry record is that numerical results for the primary antibody endpoint are not reported. There are no posted group-specific titers, treatment contrasts, confidence intervals, or hypothesis tests. Without these, neither the direction nor magnitude nor precision of the immune-response comparison can be assessed.

The outcome covers multiple strains and time points, but the registry record does not report a prespecified primary contrast or a multiplicity strategy. The statistical model for repeated measurements, any covariate adjustment, and the handling of assay values below the threshold are not described beyond the assignment of a titer of 10 to negative results (<1:20).

The analysis populations, missing-data amounts and methods, and sensitivity analyses are not reported in the registry record. The randomization sequence generation and allocation concealment are also not reported. Although the study is labeled quadruple-masked, the identities of the masked roles are not reported in the registry record. These gaps limit assessment of how the trial was implemented and analyzed.

The registry describes healthy volunteers between 18 and 45 years of age. That study population does not, by itself, establish how findings would apply to other populations. Safety reporting is also limited: the record provides counts but not detailed event terms, severity, timing, or the event definitions. The trial's enrollment and completion status do not resolve these missing outcome and analysis details.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Immune Responses to H5N1 Vaccine With and Without AS03 Adjuvant — NCT01578317.
• Registry record last updated 2019-02-26; status last verified 2018-09.
• Results first posted 2019-02-26.
• 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.

18. Record Summary

NCT01578317, titled Immune Responses to H5N1 Vaccine With and Without AS03 Adjuvant, is listed as a completed randomized, quadruple-masked, parallel Phase 1/Phase 2 study sponsored by the National Institute of Allergy and Infectious Diseases (NIAID). The registry record reports enrollment of 43 healthy volunteers between 18 and 45 years of age.

The study compared H5N1 vaccine with AS03 adjuvant against H5N1 vaccine without adjuvant. Both groups were scheduled for an initial vaccination on day 1 and a booster on day 21. The primary outcome was geometric mean antibody-neutralization titers, with standard deviation recorded as the dispersion measure, at days 0, 21, 42, and 100 against five H5N1 virus strains.

The trial began on 2012-03-20, and primary completion was recorded as 2016-01-31. Numerical antibody outcomes and statistical analyses are not reported in the registry record. Safety entries record no serious adverse events or deaths in either group, and report other adverse events in both groups.