Safe Administration of Flu Vaccine to Egg Allergic Children: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Safe Administration of Flu Vaccine to Egg Allergic Children (NCT01264601), a randomized na study. The primary outcome is Categorical Reactivity to Vaccine as it Was Administered.

2. Clinical Question

3. Trial Design

The registry identifies this as a completed, randomized, parallel-group trial of trivalent influenza vaccine in children and young adults with egg allergy. Enrollment is recorded as 31. The study started in 2010-10, and primary completion is recorded as 2012-05. The phase is listed as NA. The sponsor is the University of Michigan.

Participants were assigned to one of two administration approaches. The “Graded Challenge” arm is described as receiving the vaccine in two steps, usually 10% followed by 90% of the age-appropriate dose, separated by 30 minutes. The “Single Dose” arm is described as receiving saline in place of an initial small vaccine dose, followed by the full age-appropriate vaccine dose after 30 minutes. For children receiving a 0.25 ml dose, both descriptions note a 20%/80% split. The record also says that participants could receive a booster vaccination as a single dose if required, but does not report how many participants received a booster or how booster outcomes were handled.

The masking field lists triple masking. The brief study summary describes the planned study as double blind. These descriptions do not match, and the registry record does not explain the difference or specify which roles were masked. Allocation concealment procedures, the randomization sequence method, and details of stratification are not reported in the registry record.

The primary outcome timeframe is 48 hours. The description includes reactions observed during in-office observation and adverse reactions reported during the following 48 hours. The registry lists one secondary outcome concerning atopic co-morbidities and severe reactivity, but does not provide its result. A detailed statistical analysis plan is 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: After informed consent process, parents filled out a questionnaire, detailing their child's history of past reactions to the ingestion of egg and any prior influenza vaccines. This information was verified by medical record review. In addition, the most recent egg skin test and serum egg protein specific IgE were also obtained.

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 Categorical Reactivity to Vaccine as it Was Administered, measured over 48 hours.

The primary outcome is titled “Categorical Reactivity to Vaccine as it Was Administered,” with participants as the unit. The outcome description focuses on reactions after the assigned vaccine-administration approach. It includes observation after the doses and collection of adverse reactions during the 48 hours after vaccination that were not observed at the time of in-office observation.

A categorical reactivity outcome can distinguish types or levels of response rather than reducing every participant’s experience to a single continuous measurement. Such an outcome may be useful when the clinical question concerns whether a reaction occurred or what kind of reaction was observed. However, the registry does not provide the categories, their definitions, or category-specific results. It also notes that the primary outcome has several categories or time points and was not reduced to one comparison. The available record therefore does not establish a single primary-effect estimate or a direct statistical contrast between arms.

For this safety question, the stated observation period matters because the endpoint includes reactions reported after participants leave in-office observation. The registry identifies a 48-hour timeframe, but does not report details about how reports were collected, whether all participants completed follow-up, or how missing outcome information was handled. The endpoint description indicates what the study intended to measure; it is not, by itself, evidence of the frequency or severity of reactions.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does randomization contribute?

Random allocation is intended to make assigned groups comparable, on average, with respect to both measured and unmeasured characteristics. In a randomized trial, this supports interpretation of an adequately conducted between-group comparison. It does not guarantee that groups will be identical, particularly in a small study, and it does not replace reporting participant flow, outcome data, and an appropriate analysis. The registry records randomized allocation and a parallel model. The method used to generate the allocation sequence and the procedures used to conceal assignments are not reported in the registry record.

What is the contrast being studied?

The two arms differ in how the initial portion of vaccination was administered. In the Graded Challenge arm, vaccine was divided into two steps. In the arm labelled Single Dose, saline was used for the initial step and the full vaccine dose followed. Both approaches include an interval of 30 minutes, and the registry describes a different split for the 0.25 ml dose. Because the comparison is between these assigned procedures, a causal interpretation would depend on participants being analysed according to a clearly specified randomized-group strategy and on outcome ascertainment being sufficiently complete. The analysis strategy is not reported in the registry record.

Why does the outcome structure matter?

A categorical endpoint can capture distinct kinds of reaction, but it requires clear category definitions and a clear rule for assigning participants to categories. If categories overlap, or if observations across time points are counted differently, the analysis must specify how those data contribute to the comparison. The registry identifies categorical reactivity and a 48-hour timeframe, but does not report the categories, their coding rules, or a single primary contrast. It also states that the primary outcome has several categories or time points and was not reduced to one comparison. Consequently, no single primary effect estimate can be interpreted from the posted record.

How should uncertainty be assessed?

General statistical principle: an estimate describes the observed data, while a confidence interval describes the precision of an estimate under the assumptions of the analysis. A narrow interval indicates greater precision than a wide one; an interval that includes values compatible with different conclusions may leave substantial uncertainty. A p-value, when used, measures how unusual data at least as extreme as those observed would be under a specified null model. It does not measure the probability that a treatment is safe, nor does it measure the size or importance of an effect. The registry reports no confidence interval or p-value for the primary outcome or the adverse-event comparison.

The recorded serious and other adverse-event counts are descriptive. General statistical principle: sparse binary outcomes often yield imprecise estimates, so counts should not be read as proof that the underlying risks are equal or absent. A formal comparison would need to define the event outcome, analysis population, handling of missing observations, and method for estimating uncertainty. Those details are not reported in the registry record.

What do the planning assumptions mean?

The registry describes a sample-size planning illustration based on the observed effect, with a two-sided significance level of 0.05, equal allocation, and a normal approximation. It says the effect to detect is a stated fraction of the observed effect. For time-to-event outcomes, the planning convention is total events; for other outcomes, it is participants per arm. These are planning illustrations, not observed power and not proof that a study had sufficient power. The registry record does not report the trial’s own sample-size justification, nor does it provide the numerical planning illustrations in the available record. No planning result can therefore be assessed.

General statistical principle: a planning calculation depends on assumptions about the outcome, the effect to detect, allocation, significance level, and the statistical method. A calculation based on an observed effect is a retrospective planning illustration; it should not be presented as the trial’s original design rationale. If a trial is small or the outcome is rare, a non-significant result—if one were reported—would not by itself show that the approaches are equivalent. Equivalence or non-inferiority requires a defined margin and a design and analysis suited to that question. Such a margin is not reported in the registry record.

What remains unclear about analysis?

The registry records zero analyses. It does not report the statistical model, any adjustment variables, the handling of repeated observations or multiple categories, or the approach to missing data. It does not report interim analyses or a complete statistical analysis plan. These omissions prevent assessment of whether the analysis followed a prespecified plan and how the primary outcome was intended to be summarized. The posted counts can be described, but they do not supply the missing inferential framework.

10. Multiplicity, Missing Data and Analysis Populations

The primary outcome is described as having several categories or time points, and the registry indicates that it was not reduced to one comparison. It does not report which categories were analyzed, whether any were designated as primary components, or how a primary conclusion would be drawn across them. If multiple outcomes or comparisons are tested, the chance of at least one apparently notable result can increase. General statistical principle: a multiplicity strategy may control that risk, but the appropriate approach depends on the scientific question and analysis plan. No such strategy is reported in the registry record.

The record lists one secondary outcome concerning the influence of atopic co-morbidities on severe reactivity. Its result and analysis are not reported. The registry also records zero analyses, so it does not provide inferential results for the primary or secondary outcomes. Interim analyses and any stopping rules are not reported in the registry record.

Missing-data handling is also not described. The primary outcome includes follow-up through 48 hours, but participant-level completion, losses to follow-up, and missing outcome counts are not reported. The record does not say whether missing outcomes were excluded, imputed, or handled through another approach. Nor does it define analysis populations such as intention-to-treat or per-protocol. Without these details, it is not possible to determine how incomplete follow-up might affect the reported event counts or any intended comparison.

These omissions do not change the descriptive counts that the registry records, but they limit the ability to interpret them as a complete comparative analysis. A reader cannot determine how multiplicity, missing observations, or analysis-population choices were addressed.

11. 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 non-serious adverse event terms

The registry reports serious adverse events for each arm as counts among participants at risk. It records zero affected participants among 17 at risk in the Single Dose arm and zero among 14 at risk in the Graded Challenge arm. For other adverse events, it records one affected participant among 17 at risk in the Single Dose arm and two among 14 at risk in the Graded Challenge arm. The serious-event terms list contains no terms.

These fields distinguish serious from other adverse events, but the registry does not define the seriousness criteria or name the non-serious events. The counts describe what was recorded; they are not a statistical comparison, and no uncertainty intervals or significance tests are reported for them. A zero count means no event was recorded in that group during the reported collection, not that the underlying possibility of an event has been ruled out.

The registry’s primary endpoint is broader in description: categorical reactivity to vaccine as administered, including reports during the 48 hours after vaccination. The adverse-event fields should not be assumed to capture every category of that endpoint or to substitute for its missing results.

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

The registry describes a randomized comparison of two ways to administer trivalent influenza vaccine to participants with a documented history of severe egg allergy. The posted adverse-event fields record no serious adverse events in either arm and a small number of other adverse events. Those observations are relevant as descriptive safety information, but the record does not give a formal estimate comparing the assigned approaches.

The primary outcome was intended to capture categorical reactivity after vaccination, including reactions reported over 48 hours. However, the categories and their results are not reported in the registry record, and the registry notes that the outcome was not reduced to one comparison. The record therefore does not provide the information needed to assess the primary question with an effect estimate and a measure of precision.

The counts do not establish that the administration approaches are equivalent, that the risk of a reaction is absent, or that one approach is safer than the other. A lack of a reported serious event is not proof of zero risk. Conversely, the presence of other adverse events does not by itself show that either administration approach caused them; the registry does not report event descriptions or a causal assessment.

The trial’s brief summary states that the investigators intended to examine vaccine administration in participants with severe egg allergy and the possible relationship of adverse outcomes to ovalbumin content. The available results do not report an analysis of ovalbumin content or a result addressing that objective. The record should be read as a description of the trial design and limited event counts, not as a complete answer to the broader safety question.

For clinical interpretation, the most important statistical distinction is between an observed count and a precise estimate of underlying risk. The record gives counts but no confidence intervals, no inferential comparison, and no detailed account of follow-up completeness. The findings as posted are therefore descriptive and leave substantial uncertainty about comparative outcomes.

13. Why This Trial Matters Statistically

This trial raises a statistical challenge common to studies of uncommon safety outcomes: informative conclusions depend not only on whether events were observed, but also on how the outcome was defined, how completely it was measured, and how precisely the comparison was estimated. The registry provides adverse-event counts and a 48-hour primary-outcome timeframe, but does not provide the primary categorical results or an inferential comparison.

The randomized design is relevant because it aims to compare two administration procedures in parallel groups. Interpreting that comparison requires details about allocation, masking, follow-up, and analysis. The record identifies randomization and lists triple masking, while the brief summary describes the study as double blind. It does not explain the mismatch. Such details matter because outcome assessment and participant reporting can influence the recording of reactions.

The trial also illustrates why “no recorded serious events” and “no risk” are not interchangeable statements. General statistical principle: observed data are subject to sampling uncertainty, and sparse events can leave a wide range of underlying risks plausible. Reporting event definitions and uncertainty estimates helps readers distinguish a reassuring observation from evidence precise enough to exclude clinically meaningful possibilities.

Finally, the registry describes a multi-category primary outcome but does not provide category-level results or an analysis plan. This leaves readers unable to see whether the outcome was handled as intended or how multiple components were combined. Clear outcome definitions, transparent participant flow, and prespecified comparative analyses are especially important when a study’s central question concerns safety and the available event counts are limited.

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 registry record does not report the primary endpoint’s category definitions or category-specific results. It also states that the primary outcome has several categories or time points and was not reduced to one comparison. This prevents interpretation of a single primary effect estimate and makes it difficult to connect the reported adverse-event counts to the full primary endpoint.

Participant flow and analysis populations are not described. Although enrollment is recorded as 31 and arm-specific at-risk counts are listed for adverse events, the record does not explain the relationship between enrollment, randomization, receipt of vaccination, follow-up completion, and inclusion in each outcome count. Missing outcome information and its handling are not reported.

The record does not name the non-serious adverse events or define serious-event criteria. It does not report confidence intervals, p-values, or another formal comparison for the adverse-event counts. It also does not report the randomization sequence method, allocation concealment, or a complete statistical analysis plan. The masking descriptions differ: the masking field says triple, while the brief summary says double; the record does not reconcile them.

There is no reported result for the secondary outcome concerning atopic co-morbidities, and no reported analysis addressing the stated objective related to ovalbumin content. The registry does not report the trial’s own sample-size justification, interim analyses, or how any required booster vaccination was incorporated into outcome assessment. These limitations leave the posted record useful for describing the design and selected event counts, but insufficient for a detailed assessment of comparative safety or the full primary question.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Safe Administration of Flu Vaccine to Egg Allergic Children — NCT01264601.
• Registry record last updated 2017-10-26; status last verified 2017-09.
• Results first posted 2017-10-26.
• 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

The registry record describes a completed, randomized, parallel-group trial sponsored by the University of Michigan, with enrollment recorded as 31. It compares a graded two-step trivalent influenza vaccine challenge with an arm labelled Single Dose, in which saline precedes the full vaccine dose. The study concerns participants with a history of severe egg allergy, and the primary outcome is categorical reactivity assessed over 48 hours.

The adverse-event fields record zero serious adverse events in both arms and report other adverse events in each arm. The record does not provide category-level primary outcome results, a formal statistical comparison, uncertainty intervals, or details about missing data and analysis populations. Its descriptions of masking differ, and the reason is not reported in the registry record. The posted information supports a descriptive account of the design and recorded events, but not a precise comparative conclusion.