Systems Biology of Flu Vaccine in Healthy Adults With and Without the Use of Antibiotics: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Systems Biology of Flu Vaccine in Healthy Adults With and Without the Use of Antibiotics (NCT02154061), a randomized na study. The primary outcome is Number of Participants With Four Fold Rise in HAI Titers or HAI 1:40 and Above in Each Group at D30.

2. Clinical Question

3. Trial Design

The registry describes a randomized, parallel-group study with no masking. It compares IIV given with antibiotics against IIV given without antibiotics. The study is listed as completed, with Emory University as sponsor. The phase is recorded as NA. The registry lists Influenza as the condition.

The brief summary describes the scientific motivation as understanding whether antibiotics change intestinal microorganisms and whether those changes may alter the body’s response to seasonal flu vaccination. The investigators planned to examine blood markers after vaccination. The intervention arm was to receive antibiotics before and after IIV administration; the other arm was to receive IIV without antibiotics. Metronidazole, neomycin and vancomycin appear in the intervention list, but doses, exact drug combinations and treatment assignments are not reported in the registry record.

The registry gives a start date of 2015-04 and a primary completion date of 2017-05-26. It records enrollment of 33; the brief summary says investigators hoped to enroll 50 subjects at Emory. The day-30 primary-outcome results include 15 participants in the antibiotic group and 17 in the vaccine-only group. For the antibiotic group, the outcome description explains that one participant received antibiotics but not vaccine and lacked a blood draw on vaccination day, so she was included in the safety population but not the immunologic population.

Randomization helps create a basis for comparing assigned groups, but the registry does not report sequence generation, allocation concealment, adherence, or other implementation details. With no masking, participants and study personnel were not masked according to the recorded design. The statistical analysis plan and the methods used to analyze the endpoint 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.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: The Overall Number of Participants analyzed for "IIV Flu Vaccine with Antibiotics" is 15, as one participant received antibiotics and did not receive vaccine. The study personnel were unable to draw blood on her at the vaccination day- therefore she was part of the safety population and not the immunogenicity 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.

6. Primary Endpoint

The registry lists the primary outcome as Number of Participants With Four Fold Rise in HAI Titers or HAI 1:40 and Above in Each Group at D30, measured over At day 30.

The primary endpoint is the number of participants in each group who, at day 30, met either of two HAI antibody criteria: a fourfold rise in HAI titers or an HAI titer of 1:40 and above. HAI refers to the hemagglutination-inhibition antibody test; the registry describes the endpoint as based on immunologic testing of blood samples.

The endpoint combines the two criteria using “or.” A participant meeting either criterion is counted as meeting the endpoint. The results therefore concern a participant count, not the size of each person’s titer change, a continuous antibody measurement, or a clinical influenza outcome. The registry record does not report separate counts for the two component criteria, so it is not possible to tell how many participants qualified by a fourfold rise, by reaching the stated titer threshold, or by both.

Using a blood-based immune marker allows investigators to assess a biological response following vaccination. In general, a prespecified binary endpoint can make a group comparison easier to interpret as the number meeting a defined criterion. However, the registry does not explain why this particular combined endpoint was selected, whether it was prespecified in a protocol, or how it relates to clinical protection. The posted result should therefore be read as an immunologic endpoint result, not as a count of influenza cases prevented or a direct measure of vaccine effectiveness.

7. Results Posted in the Registry

• IIV Flu Vaccine: 100.0% (17/17) versus 100.0% (15/15) on control; risk difference 0.0 percentage points (95% CI 0.0 to 0.0), risk ratio 1.00 (1.00–1.00); unadjusted two-proportion z-test p = n/a.

8. Statistical Interpretation

9. Statistical Methods Explained

What does a risk difference describe?

In general, a risk difference compares the proportion of participants meeting an outcome in one group with the proportion in another. A value of 0.0 means the posted group proportions are equal according to that summary. Here, the registry reports a risk difference of 0.0 for the day-30 HAI endpoint. The underlying outcome is binary because each participant either meets the combined criterion or does not.

What does the risk ratio describe?

In general, a risk ratio expresses one group’s event proportion relative to the other group’s event proportion. A value of 1.0 indicates equal proportions in the comparison as reported. The registry reports a risk ratio of 1.0, with an interval from 1.0 to 1.0. This is a relative summary of the same endpoint, not a separate clinical outcome. Neither a risk difference nor a risk ratio conveys the antibody-titer values of individual participants.

How should the p-value be read?

In general, a p-value describes how compatible data are with a specified null model, given the assumptions of the test. It is not the probability that a treatment has no effect, and it does not measure the size or clinical importance of an effect. The registry reports p = 1.0 for the comparison. The statistical test, its assumptions, and whether the p-value is adjusted are not reported in the registry record. Therefore, the p-value cannot be fully evaluated from the posted summary alone.

Why do confidence intervals matter?

In general, a confidence interval communicates the range of estimates compatible with a method and the observed data, under its assumptions. It can help readers judge precision and distinguish a narrow estimate from one that leaves substantial uncertainty. The registry’s risk-difference interval is 0.0 to 0.0, and the risk-ratio interval is 1.0 to 1.0. Because the analysis method is not reported and each interval has equal endpoints, these entries do not allow a conventional assessment of sampling uncertainty. They should be described as the values recorded rather than treated as proof of certainty.

What does randomization contribute?

In general, random assignment is intended to make groups comparable with respect to both measured and unmeasured baseline characteristics, on average. This supports causal interpretation when implementation, follow-up, outcome measurement and analysis are also appropriate. The registry labels this study randomized, but does not report the randomization procedure or allocation concealment. It also records no masking. Randomization is a design feature, not a guarantee that every source of bias has been removed.

What can be inferred from a count endpoint?

For a binary endpoint, a count is meaningful only alongside the group denominator and a clear definition of who was analyzed. The registry gives the primary-outcome group sizes and counts, and describes the combined HAI criteria. It does not report separate results for each criterion. The outcome is assessed at day 30; the registry does not describe additional time points for this primary measure or provide individual-level data. The summaries cannot show the spread of antibody responses or identify whether a participant met one criterion or both.

How should planning illustrations be understood?

In general, sample-size calculations depend on assumptions about the effect to detect, the significance level, allocation, and statistical method. The registry’s planning assumptions describe an 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 described as a fraction of the observed effect. Such calculations are planning illustrations, not observed power and not evidence that the study was designed around a specified clinical difference. No particular planning result or protocol-based sample-size justification is reported in the registry record.

What is missing from the analysis description?

The registry lists no detailed analysis records. It does not report the statistical test, model specification, covariate adjustment, missing-data method, handling of protocol deviations, or prespecified analysis plan. Those omissions limit reproducibility and make it difficult to determine whether the comparison was planned in advance or how robust it is to alternative reasonable analytic choices. The posted summaries remain interpretable as registry results, but they do not supply the methodological detail needed for a complete statistical audit.

10. Confidence Intervals and Precision

The group counts are 15 participants meeting the endpoint in the antibiotic-plus-IIV arm and 17 in the IIV-only arm. The corresponding primary-outcome group sizes are 15 and 17. The registry’s comparison summaries report a risk difference of 0.0 and a risk ratio of 1.0, with p = 1.0. These values describe equality in the posted group proportions for this endpoint.

Precision is usually assessed by looking at how much plausible effect estimates vary around the observed estimate. In general, a confidence interval gives a range of values compatible with the data and the procedure used to calculate it. The posted risk-difference interval runs from 0.0 to 0.0; the risk-ratio interval runs from 1.0 to 1.0. Both are collapsed to their point estimates. The method used to construct them is not reported in the registry record, so their statistical behavior cannot be assessed from the record. They should not be read as demonstrating that the true effect is known without uncertainty.

The registry lists an enrollment of 33, while the primary-outcome results give the analyzed group sizes and describe an antibiotic-treated participant who did not receive vaccine and had no blood draw on vaccination day. The record says she was in the safety population but not the immunologic population. Details about any other missing outcome data, reasons for missingness, or sensitivity analyses are not reported. That limits assessment of whether the analysis groups fully represent the randomized participants.

With the available summary, readers can describe the recorded endpoint counts and comparison estimates but cannot determine the range of effects that might be compatible with the study under a fully specified analysis. The absence of reported interval methodology and analysis details is especially important when interpreting the unusually collapsed intervals.

11. Multiplicity, Missing Data and Analysis Populations

The registry lists one primary outcome measure and no secondary outcomes. It also lists no detailed analysis records. The statistical plan for handling multiple comparisons is not reported in the registry record. Although the registry lists one primary outcome, it does not establish whether additional outcomes or analyses were planned outside the posted record. The reported p-value should therefore be interpreted as the registry’s comparison summary, without assuming whether multiplicity was considered.

The primary-outcome description identifies an immunologic analysis group of 15 in the antibiotic arm and 17 in the vaccine-only arm. It states that one participant received antibiotics but did not receive vaccine and had no blood draw on vaccination day; she was included in the safety population and not the immunologic population. The registry record does not report a complete participant flow, the number randomized to each group, or a full account of exclusions from each analysis population.

Methods for handling missing primary-outcome data are not reported. The record does not describe imputation, sensitivity analyses, or how any other missing blood samples would have been handled. It also does not state whether analyses followed randomized assignment or another analysis-population definition. Consequently, readers cannot assess from the record whether missingness could affect the endpoint comparison.

Safety denominators differ from the immunologic group sizes: the adverse-event record lists 16 participants at risk in the antibiotic group and 17 in the vaccine-only group. The outcome description explains the safety inclusion of the participant who lacked the vaccination-day blood draw. Other details about safety-population definitions are not reported. These distinct analysis populations should not be conflated when interpreting efficacy-related and safety counts.

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 registry reports zero serious adverse events in each group and zero deaths in each group. The serious-event risk sets are 16 participants for IIV with antibiotics and 17 for IIV alone. These are safety figures, not the immunologic analysis denominators. The registry also lists six participants affected by other adverse events in the antibiotic group and three in the vaccine-only group, with risk sets of 16 and 17, respectively.

These counts describe what the registry records; they do not establish that the interventions caused the events or that there were no unrecorded events. The registry does not provide serious adverse-event terms, and the list of top serious terms is empty. It does not report event definitions, severity grading, timing, relationship to treatment, or the method used to collect adverse events. Zero reported serious events should therefore be read as a finding in the posted safety record, not as proof that serious harms are impossible.

Other adverse events are reported separately from serious adverse events. The numbers affected are counts, not percentages, and should be read with their stated risk sets. No statistical comparison or causal analysis of these safety counts is reported in the registry record.

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

The posted result answers a narrow question: how many participants in each recorded immunologic group met the combined HAI criterion at day 30? The registry reports 15 of 15 in the antibiotic-plus-vaccine group and 17 of 17 in the vaccine-only group, with a risk difference of 0.0, risk ratio of 1.0 and p = 1.0. This is a description of the primary endpoint as recorded, not a broad conclusion about immune function.

The result does not show whether the antibiotic regimen changed intestinal microorganisms, because no microbiome result is included in the registry record for this endpoint. It does not establish whether antibody titers differed in their actual magnitude, since only the binary combined criterion is reported. Nor does it provide separate counts for a fourfold rise and reaching an HAI titer of 1:40 and above.

The endpoint is an immunologic measure, not a clinical influenza outcome. The posted result does not report influenza infections, vaccine effectiveness, duration of protection, or clinical consequences. It cannot establish that antibiotics do or do not alter protection against influenza. The statistical summary also does not prove the groups are equivalent: the registry does not report a prespecified equivalence margin or a noninferiority framework, and its intervals are collapsed with no stated method.

The study concerns healthy adults and was conducted at Emory University, so the record does not establish applicability to other populations or settings. The study is listed as randomized, but the lack of detail on allocation procedures, analysis methods and missing data constrains interpretation. The accurate conclusion is limited to the recorded endpoint counts and comparison; broader biological or clinical claims are not supported by the posted results alone.

14. Why This Trial Matters Statistically

This study illustrates why endpoint definitions and analysis populations matter in clinical biostatistics. The primary outcome is a combined binary criterion: a fourfold rise in HAI titers or an HAI titer of 1:40 and above at day 30. The combined count makes the result compact, but without component-specific counts it conceals which criterion participants met. That distinction can matter when interpreting the biological response.

The record also makes clear that the population used for immunologic results need not be the same as the safety population. One participant in the antibiotic arm received antibiotics but not vaccine and could not provide a vaccination-day blood sample; the outcome description excludes her from the immunologic population but includes her in safety. Readers need these population details to interpret counts and denominators correctly.

The comparison summaries demonstrate the importance of uncertainty reporting. The registry lists a risk difference of 0.0 and an interval from 0.0 to 0.0, but does not report the interval method. An interval that collapses to the point estimate cannot, without methodological context, be treated as a complete account of uncertainty. Detailed analysis records are also absent, making transparent statistical interpretation harder.

Finally, the registry’s planning assumptions are illustrations based on the observed effect rather than a reported study-design justification. Planning calculations and observed results answer different questions. Clear protocol-level assumptions, analysis methods, missing-data handling and endpoint-component reporting would make the findings easier to evaluate and reproduce.

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 registry record does not report the statistical analysis plan, the test used for the primary comparison, any covariate adjustment, or the method used to calculate the reported intervals. The interval endpoints are identical for both the risk difference and risk ratio, and the record does not explain this. This prevents a complete assessment of uncertainty and the statistical procedure.

The primary outcome combines two HAI criteria, but results for each criterion separately are not reported. The registry also does not provide individual titers, change scores, or information about the distribution of antibody responses. The endpoint is limited to day 30, and no clinical influenza outcome is included in the posted results.

The outcome description notes one participant in the antibiotic arm who received antibiotics but did not receive vaccine and lacked a blood draw on vaccination day. The participant was excluded from the immunologic population and included in safety. A full flow of participants, details for other missing data, and sensitivity analyses are not reported. Allocation concealment, adherence, antibiotic dosing and the specific use of the listed drugs are also not reported.

The study is recorded as randomized and unmasked. The record does not give enough detail to assess randomization implementation or the potential effect of unmasked treatment on other study procedures. Enrollment is listed as 33, while the summary states that investigators hoped to enroll 50 subjects at Emory; no sample-size justification is reported. Together, these limitations mean that the posted comparison is informative as a registry result but does not support detailed judgments about robustness, generalizability, or clinical effect.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Systems Biology of Flu Vaccine in Healthy Adults With and Without the Use of Antibiotics — NCT02154061.
• Registry record last updated 2018-08-15; status last verified 2018-07.
• Results first posted 2018-06-27.
• 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

NCT02154061 is a completed randomized, parallel-group, unmasked study sponsored by Emory University. It compared inactivated influenza vaccine with antibiotics against vaccine without antibiotics in healthy adults. The registry lists enrollment of 33 and a primary completion date of 2017-05-26.

The primary endpoint was the number meeting either a fourfold rise in HAI titers or an HAI titer of 1:40 and above at day 30. The registry reports counts of 15 in the antibiotic-plus-vaccine arm and 17 in the vaccine-only arm. The comparison summary reports a risk difference of 0.0, risk ratio of 1.0 and p = 1.0. The stated intervals have identical endpoints; the method is not reported.

The safety record lists zero serious adverse events and zero deaths in each group, and reports other adverse events affecting six participants in the antibiotic group and three in the vaccine-only group. Detailed analysis methods, missing-data procedures and protocol-level statistical plans are not reported in the registry record.