Serologic Assay Validation, Proficiency Testing, Safety and Immunogenicity of Norovirus GI.1/GII.4 Bivalent Virus-Like Particle Vaccine: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Serologic Assay Validation, Proficiency Testing, Safety and Immunogenicity of Norovirus GI.1/GII.4 Bivalent Virus-Like Particle Vaccine (NCT02475278), a na phase 2 study. The primary outcome is Number of Participants With Serum Samples Obtained on Day 8 for Assessment of Seropositivity for Both Anti-NoV GI.1 VLP and GII.4 VLP Antibodies.

2. Clinical Question

3. Trial Design

This completed phase II study was registered as a single-arm, open-label trial. The registry lists 50 participants enrolled, no allocation to competing groups, and no masking. The study dates are 2015-02-26 for its start and 2015-04-07 for primary completion. These design features frame how its results can be interpreted: observations describe the vaccinated group, rather than a randomized contrast between vaccine and control.

The intervention was the NoV GI.1/GII.4 bivalent VLP vaccine, given as an intramuscular injection once on Day 1. The registry describes a formulation with 15 µg of GI.1 norovirus VLP and 50 µg of GII.4 norovirus VLP, adjuvanted with 500 µg aluminum hydroxide. The study population is described as healthy participants, and the listed conditions include norovirus and healthy participants.

The stated purpose was to collect serum samples for evaluation of serologic assays and to establish proficiency panels for assays used to assess post-vaccination immune response. In particular, the primary endpoint concerns the availability of baseline and Day 8 measurements for both antibody targets and both assay approaches. The registry identifies the safety analysis set as all participants who received the vaccine. It does not report how many participants had complete paired samples or the resulting assay values.

Safety outcomes listed include solicited local and systemic adverse events by maximum severity, elevated daily oral temperature, unsolicited adverse events by maximum severity, and serious adverse events. Those listed outcomes indicate what the study intended to monitor; they do not, by themselves, give each outcome’s observed result. Detailed results for these measures are not reported in the registry record.

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: Healthy volunteers were enrolled in 1 treatment group and received a single dose of NoV Vaccine (15 µg of GI.1 norovirus VLP and 50 µg GII.4 norovirus VLP, adjuvanted with 500 µg aluminum hydroxide).

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Safety Analysis Set, all participants who received the trial vaccine (NoV Vaccine).

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: Safety Analysis Set, all participants who received the trial vaccine (NoV Vaccine).

6. Primary Endpoint

The registry lists the primary outcome as Number of Participants With Serum Samples Obtained on Day 8 for Assessment of Seropositivity for Both Anti-NoV GI.1 VLP and GII.4 VLP Antibodies, measured over Day 8.

The primary endpoint is the number of participants with serum samples obtained on Day 8 for assessment of seropositivity for both anti-NoV GI.1 VLP and GII.4 VLP antibodies. The endpoint description specifies that participants were to have measurements for both antibody targets using both the pan-Ig enzyme-linked immunosorbent assay and the histoblood group antigen binding assay, with values available at baseline and Day 8.

This endpoint is useful for describing whether paired samples were available for the planned assay assessment. Paired measurements allow an assay evaluation to consider results from the same participant at baseline and after vaccination. Including both antibody targets and both assay approaches also makes sample availability relevant to the stated aim of evaluating serologic assays and establishing proficiency panels.

The endpoint should not be confused with the number who tested seropositive or with the magnitude of an immune response. Its title focuses on participants with the required samples for assessment. The record’s description says the antibody assays were used to assess seropositivity, but the endpoint result and assay values are not reported in the registry record. No seropositivity rate, change from baseline, or assay agreement result can therefore be described from the registered information.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does a count endpoint represent?

In general, a count endpoint records how many participants meet a stated condition. Here the condition is having serum samples available on Day 8 for assessment of both antibody targets with both assay methods, alongside baseline and Day 8 values. Such a count is different from a continuous laboratory result, such as an antibody concentration, and different from a binary seropositivity result. The count describes completion of a defined set of assessments; it does not reveal the assay values themselves.

To interpret a count fully, readers need to know the eligible analysis population and the denominator against which the count is understood. The registry describes the safety analysis set, but does not report a numerical primary endpoint result or its analyzed denominator. It is therefore not possible to characterize the rate of complete paired sample availability from the registry record.

What is the role of the two assays?

The endpoint description names the pan-Ig ELISA and the HBGA binding assay as methods for assessing antibodies to GI.1 VLP and GII.4 VLP. In general, two assays can be evaluated for how they classify or quantify the same specimens. Their agreement, relative performance, and ability to identify seropositivity require observed assay results and a stated analysis approach. Neither the assay names nor the sample-availability endpoint alone establishes those properties.

Baseline and Day 8 values make paired assessment possible. In general, paired observations compare measurements within the same participant across time, which can account for stable differences between participants. However, the registry record does not report the paired measurements, the number of complete pairs, or an analysis of change. No direction or size of an immune response can be inferred from the endpoint title.

Why does the single-group design matter?

In general, a single-group study describes what was observed among participants receiving the intervention. A randomized comparator can help separate intervention-associated differences from background changes and other influences. This study has no registered comparison group, so an estimate of a difference between vaccine and control groups is not available. Open-label status also means masking is listed as none; the registry does not describe any blinded assessment procedure.

The design is consistent with the stated objective of collecting samples for assay evaluation and proficiency panels, but it does not make every possible clinical inference available. Its primary outcome concerns specimen availability, and the secondary outcomes listed concern safety. The record does not report analyses of clinical protection or comparative effectiveness.

How should uncertainty be understood?

In general, a confidence interval describes a range of values compatible with the observed data under a specified statistical model. Its width reflects precision, while its interpretation depends on the outcome, analysis population, and assumptions. The registry record does not report a confidence interval for the primary endpoint or assay outcomes. Without the observed count and denominator, precision cannot be assessed.

For event outcomes, uncertainty also depends on how many events and participants were observed and how the analysis handles follow-up and event definitions. Small event counts can leave substantial uncertainty even when a percentage is reported. The adverse-event entries are descriptive; the record does not provide a comparative statistical estimate or interval for them.

What do planning illustrations mean?

In general, sample-size planning asks how many participants a future study may need under specified assumptions about an effect, allocation, significance level, and statistical model. The registry’s planning assumptions describe illustrations based on a fraction of an observed effect, two-sided significance level 0.05, equal allocation between two arms, and a normal approximation. They are planning illustrations, not results from this single-group trial and not observed power.

Those assumptions describe a hypothetical two-arm design, while the registered study is single group. Thus, such planning values should not be read as the number enrolled in this study, nor as evidence that the trial could detect a particular effect. A sample-size illustration depends on its assumed effect and model; the registry record does not report a sample-size justification for the trial’s actual design.

What analysis details are absent?

The registry record reports no analyses in the analysis count. It does not describe a statistical analysis plan, a method for handling missing data, interim analyses, or a multiplicity adjustment. Those details are not reported in the registry record. They should not be inferred from the endpoint wording or from the presence of multiple registered outcomes.

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("NoV Vaccine")
n      <- c(50)
events <- c(48)
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  NoV Vaccine  50  48  96.0  86.3  99.5  86.5  98.9  86.5  98.8

11. Multiplicity, Missing Data and Analysis Populations

The registry lists a primary endpoint and several safety outcomes, including local and systemic solicited adverse events, elevated daily oral temperature, unsolicited adverse events, and serious adverse events. Considering multiple outcomes can raise multiplicity concerns when many statistical tests are used to support confirmatory claims. In general, multiplicity methods control the chance of false-positive findings across a defined family of tests. The registry record does not report a multiplicity strategy or a statistical analysis plan, so it is not possible to say whether any adjustment was planned or used.

Missing data are especially relevant to the primary endpoint because it requires baseline and Day 8 values for both antibody targets and both assay methods. A participant lacking one required measurement would not meet the endpoint’s stated sample-availability condition. The record does not report the number with complete assessments, the amount or pattern of missing samples, reasons for missingness, or an imputation method. Those details are not reported in the registry record.

The registry describes the safety analysis set as all participants who received vaccine. It does not provide further analysis-population definitions for the primary endpoint or assay evaluations. The adverse-event summary identifies 50 as at risk in each of its displayed categories, but that does not establish the denominator used for every other outcome. In general, an analysis population and its denominator should be explicit because they determine which participants contribute to each estimate.

The record indicates no analyses in its analysis count. Accordingly, no reported inferential procedure, missing-data method, or adjustment for multiple outcomes can be summarized. Absence of those details in the registry record should be treated as unreported information, not as proof that no such methods were used outside the record.

12. Safety Results

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

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 5% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: unevaluable event (2.0%).

The registry’s adverse-event summary lists 1 participant affected among 50 at risk for serious adverse events and 3 affected among 50 at risk in the other adverse-event category. It also lists “Unevaluable event” as a serious-event term, with 2.0% recorded. These entries are descriptive registry data. The record does not provide enough detail to reconcile event terms with individual participants or explain the classification of an unevaluable event.

The presence of an event in a post-vaccination summary does not establish that vaccination caused it. A single-group study has no concurrent control group for estimating how event frequency compares with background occurrence or another intervention. The registry record also does not give detailed results for each listed solicited and unsolicited safety outcome, or explain follow-up completeness in the safety summary.

In general, adverse-event counts and percentages should be read with their definitions, denominator, observation period, and severity criteria in mind. The registry lists outcomes by maximum severity for several categories, but the detailed category results are not reported in the registry record. These figures describe what is recorded; they are not, on their own, a controlled assessment of safety.

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

This study’s stated purpose was to collect serum samples for serologic assay evaluation and to establish proficiency panels for assays used to assess post-vaccination immune response. Its primary endpoint operationalizes that aim by counting participants with the required Day 8 assessments for both antibody targets and both assay methods, with baseline and Day 8 values available. That makes the endpoint relevant to whether the planned laboratory assessment could be conducted.

The registry does not report the primary endpoint result. It also does not report assay values, seropositivity findings, assay agreement, or changes from baseline. As a result, the posted information does not establish how many participants had the specified samples, what antibody responses were observed, or how the assays performed relative to one another.

The safety data are limited to the adverse-event summary entries. Because the study is single group and open label, those entries do not provide a randomized comparison, and they cannot establish that an event was caused by the vaccine. Nor does the registry’s completed status supply missing endpoint or safety results.

In general, a laboratory sample-availability endpoint is distinct from a clinical benefit endpoint. It can address whether materials were available for assay work without answering whether vaccination prevents illness or changes a clinical outcome. No claim about clinical protection follows from the primary endpoint description. The registry record does not report such an outcome or a controlled estimate of one.

14. Why This Trial Matters Statistically

This trial is statistically notable for the distinction between an assay-readiness question and a treatment-effect question. Its primary outcome is the number of participants with the required paired serum assessments for two antibody targets and two assay methods. Such an endpoint speaks to the availability of specimens for assay validation and proficiency-panel work. It does not, by itself, summarize immune response magnitude or clinical benefit.

The single-group, open-label design also illustrates why the estimand matters. The registered study can describe observations among vaccinated participants, but it has no randomized control group for a direct treatment contrast. This is particularly important when interpreting safety events or any post-vaccination change: descriptive observations are not equivalent to a comparative estimate.

The record also demonstrates the importance of distinguishing enrollment from endpoint-specific analysis populations. Enrollment is listed as 50, while the primary endpoint requires a particular set of baseline and Day 8 measurements. The record does not report how many participants met that requirement. Likewise, adverse-event at-risk group sizes belong to the safety summary and should not automatically be treated as denominators for the laboratory endpoint.

Finally, statistical interpretation depends on the results being reported, not only on the registered purpose and endpoint wording. Without the primary count, assay results, and analysis details, readers cannot assess precision, missingness, or assay performance from this registry record. The study’s stated methodological aim is clear, but the registry information available for interpretation is limited.

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 principal limitation for interpreting the registered primary endpoint is that its observed result is not reported in the registry record. The endpoint description specifies the required Day 8 and baseline assessments, but the record gives no count of participants meeting that condition, no endpoint denominator, and no account of incomplete sample sets. Therefore, the degree of sample availability and the precision of any estimate cannot be evaluated.

The registry record also does not provide antibody assay values, seropositivity results, changes from baseline, or comparisons between the pan-Ig ELISA and HBGA binding assay. Although assay evaluation is central to the stated purpose, the available endpoint information describes sample availability rather than assay performance. Results for the listed secondary safety outcomes are not reported in detail either.

The single-group, open-label design limits causal interpretation. There is no registered concurrent control, and the record does not describe masking. Consequently, the safety counts cannot be interpreted as comparative risks, and observed post-vaccination measurements would not alone isolate an intervention effect. The registry does not report a statistical analysis plan, missing-data procedures, multiplicity handling, or a sample-size justification for the trial’s actual design.

These limitations concern what can be concluded from the registry record. They do not establish that additional study data or analyses do not exist; those details are not reported in the registry record.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Serologic Assay Validation, Proficiency Testing, Safety and Immunogenicity of Norovirus GI.1/GII.4 Bivalent Virus-Like Particle Vaccine — NCT02475278.
• Registry record last updated 2018-02-22; status last verified 2018-02.
• Results first posted 2016-10-28.
• 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

NCT02475278 is a completed phase II, single-group, open-label study sponsored by Takeda. The registry lists 50 enrolled participants and study dates of 2015-02-26 to 2015-04-07. Participants received one intramuscular dose on Day 1 of a bivalent norovirus GI.1/GII.4 VLP vaccine containing 15 µg of GI.1 VLP and 50 µg of GII.4 VLP, adjuvanted with 500 µg aluminum hydroxide.

The stated purpose was to collect serum for assay evaluation and proficiency-panel development. The primary endpoint concerns participants with the required baseline and Day 8 assessments for both antibody targets using the pan-Ig ELISA and HBGA binding assay. Its result and assay measurements are not reported in the registry record. The safety summary lists 1 participant affected among 50 at risk for serious adverse events and 3 among 50 in the other adverse-event category; a serious-event term is recorded as “Unevaluable event” at 2.0%. No randomized comparator is registered.