Evaluate the Pharmacokinetics, Safety, and Tolerability of Nirsevimab in Healthy Chinese Adults: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Evaluate the Pharmacokinetics, Safety, and Tolerability of Nirsevimab in Healthy Chinese Adults (NCT04840849), a randomized phase 1 study. The primary outcome is Serum Concentrations of Nirsevimab.

2. Clinical Question

This was a pharmacokinetic study rather than a clinical-outcome efficacy trial. Its primary question concerns the concentration of nirsevimab measured in serum at specified times, not whether a health outcome improved. The registry describes sampling before dosing on Day 1 and after dosing on Days 2, 4, 6, 8, 15, 31, 91, and 151.

The record also lists the number of participants with a positive anti-drug antibody of nirsevimab as a secondary outcome. The primary endpoint description does not establish a threshold for a meaningful concentration or identify a clinical benefit associated with any concentration. Numerical concentrations and comparative estimates are not reported in the registry record, so the primary question cannot be answered from its posted numerical results.

3. Trial Design

The registry identifies this as a Phase 1, randomized, placebo-controlled study with a parallel-group model. The official title calls it double-blind, while the registry’s masking designation is triple. These are the two masking descriptions recorded; further details about which groups were masked are not reported in the registry record.

The study evaluated a single intramuscular dose of nirsevimab against a single intramuscular dose of placebo in healthy Chinese adults. Enrollment was 24. The safety record lists 18 participants at risk in the nirsevimab group and 6 in the placebo group. The record does not describe the randomization sequence, allocation concealment, or the procedures used to maintain masking.

The listed sponsor is AstraZeneca. The study began on 2021-06-22, had a primary completion date of 2021-11-18, and is marked completed. These registry entries describe the study’s administrative status and timeline; they do not provide evidence about the magnitude or precision of the pharmacokinetic results.

Serum sampling was scheduled before dosing on Day 1 and on Days 2, 4, 6, 8, 15, 31, 91, and 151 post-dose. The primary outcome is serum concentration, summarized as a mean with standard deviation. The pharmacokinetic population was restricted to participants meeting the record’s criteria for treatment exposure, a measurable post-dose observation, and samples not considered affected by relevant factors such as important protocol deviations.

The registry lists five outcome measures, including the primary serum-concentration outcome and a secondary outcome concerning positive anti-drug antibodies. It records zero analyses. No detailed statistical analysis plan, rationale for the enrollment target, or description of any interim analysis is reported in the registry record. The available design information therefore supports a description of the intended comparison and measurement schedule, but not a reconstruction of all operational or analytical decisions.

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: This study consisted of a screening period (28 days) and treatment period (151 days). A total of 24 participants were randomized in a 3:1 ratio to receive either nirsevimab or placebo.

Overall Study

Analysis population for the primary outcome, as defined in the registry: The PK population included all participants who received any dose of study treatment and had at least one measurable post-dose serum PK observation and for whom PK blood samples were assumed not to be affected by factors such as important protocol deviations (if any, determined prior to unblinding). Only participants who received nirsevimab were analyzed for PK outcome measures.

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: As-treated population included all participants who were randomized into the study and received any amount of study treatment.

6. Primary Endpoint

The registry lists the primary outcome as Serum Concentrations of Nirsevimab, measured over Pre-dose on Day 1 and on Days 2, 4, 6, 8, 15, 31, 91, 151 post-dose..

The primary endpoint is serum concentration of nirsevimab, measured in micrograms/milliliter (mcg/mL). It is a continuous pharmacokinetic measure: the concentration of the study drug in serum at scheduled sampling times. The registry specifies that the outcome is expressed as a mean with standard deviation. Samples were collected before dosing on Day 1 and on Days 2, 4, 6, 8, 15, 31, 91, and 151 post-dose.

Concentration measurements are used in pharmacokinetic studies to describe drug exposure over time. Repeated measurements can characterize how concentrations vary across the sampling schedule. This is a general explanation of the role of the measure; the registry record does not report concentration values, a concentration-time curve, or a derived pharmacokinetic parameter such as an area under the curve or half-life.

The registry’s endpoint description says that serum samples were collected at the indicated timepoints to determine serum concentration. It defines the pharmacokinetic population as participants who received any dose of study treatment and had at least one measurable post-dose serum pharmacokinetic observation, with samples assumed not to have been affected by factors such as important protocol deviations when determined before unblinding.

The mean describes the central value of the observed concentrations, while the standard deviation describes their spread around that mean. Neither alone indicates the precision of an estimate; a confidence interval would be needed to communicate uncertainty about an estimated mean or contrast. Numerical means, standard deviations, confidence intervals, and between-group contrasts are not reported in the registry record. The endpoint therefore identifies what was measured and when, but the available record does not permit assessment of the observed concentration profile.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry identifies the primary outcome as a continuous measure: mean serum concentration of nirsevimab, with standard deviation, in micrograms/milliliter (mcg/mL). Understanding the method requires separating the observed measurements from the statistical summaries that might be calculated from them. The registry describes the measurements and their schedule, but does not report the resulting numerical summaries or analyses.

What does a mean and standard deviation describe?

For a continuous outcome, the mean summarizes the central location of the observed values. The standard deviation describes how spread out those values are around the mean. These summaries answer different descriptive questions: the mean gives a typical level under the chosen summary, while the standard deviation communicates variability among observations. A mean and standard deviation do not by themselves show how precisely the population mean has been estimated. A confidence interval is commonly used for that purpose; it gives a range of values compatible with the data and the method’s assumptions. No confidence interval is reported in the registry record.

Concentration is measured repeatedly over time in the listed schedule. A mean at a particular timepoint describes measurements at that timepoint, rather than the whole concentration-time profile. Interpreting changes over time would require the actual observations or reported summaries at the scheduled times. Those numerical results are not reported in the registry record. The record also does not report a model for repeated measurements, any adjustment for baseline values, or a derived pharmacokinetic summary.

What does the pharmacokinetic population mean?

The registry defines the pharmacokinetic population by treatment exposure, availability of at least one measurable post-dose serum pharmacokinetic observation, and an assessment that samples were not affected by factors such as important protocol deviations. The record says that any such deviations were to be determined before unblinding. This definition describes an analysis population, but the number of participants satisfying it and the rules used to handle measurements outside it are not reported in the registry record.

Restricting an analysis to observations judged suitable for pharmacokinetic assessment can help focus the analysis on measurements considered interpretable. It can also affect which participants contribute to a summary. If eligibility for the analysis depends on having a measurable observation or on decisions about protocol deviations, the analysis population may differ from the enrolled group. The consequences cannot be assessed without the population count, participant flow, and details of exclusions, none of which are reported in the registry record.

Why does uncertainty matter?

Statistical estimates from a study population are subject to sampling variability. A confidence interval communicates uncertainty around an estimate, while a standard deviation describes variability among the observed values. They are not interchangeable. A narrow interval would generally indicate greater precision under its assumptions; a wide interval would indicate less precision. These are general statistical explanations, not descriptions of results from this trial. The registry record does not report an interval for the primary endpoint, so its precision cannot be evaluated.

For repeated concentration measurements, dependence among observations from the same participant may matter. General statistical methods can account for the correlation between repeated measurements, rather than treating all measurements as independent. The choice of method affects how uncertainty is estimated and how the time course is summarized. The analysis method for this endpoint is not reported in the registry record, so it is not possible to determine whether repeated-measure dependence was modeled or how any estimates were constructed.

What can the sample-size assumptions tell readers?

The registry’s planning assumptions describe an illustration based on the observed effect, not the trial’s own design. The stated assumptions are a two-sided significance level of 0.05, equal allocation between arms, and a normal approximation, with the effect to detect specified as a fraction of the observed effect. Such illustrations are conditional planning calculations: they describe the sample size that would be associated with the stated assumptions and target effect, rather than a result observed in this trial.

Planning calculations are not observed power. Observed power is not a substitute for an effect estimate and confidence interval, and a planning illustration does not show that the trial had a particular chance of detecting an effect. The record does not report a sample-size justification for the trial’s design. It also does not report numerical planning results for the primary outcome. The illustration’s equal-allocation assumption should be understood as a planning assumption, not as a description of the safety-group denominators.

What do the reported safety counts represent?

The safety entries report the number at risk and the number affected for serious and other adverse events, together with deaths. These are counts, not estimates adjusted for duration of follow-up or exposure. A count of participants with an event does not convey the event’s timing, duration, recurrence, severity, or relationship to treatment. No serious adverse event terms are listed, and the registry reports zero participants affected by serious adverse events in both groups. The record does not provide further detail about the other adverse events.

Statistical interpretation depends on the analysis question and the data actually reported. Here, the record supplies a design description, an endpoint definition, a sampling schedule, and safety counts, but no numerical primary outcome analysis. Any inference about the magnitude, precision, or statistical significance of the pharmacokinetic comparison would therefore go beyond the registry record.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists five outcome measures and identifies serum concentrations of nirsevimab as the primary outcome. It also lists the number of participants with positive anti-drug antibody of nirsevimab as a secondary outcome. The registry record does not report a hierarchy among secondary outcomes, a multiplicity adjustment, or a strategy for controlling the chance of false-positive findings across multiple comparisons. It also records zero analyses, so no outcome-specific tests or estimates are available to evaluate.

Multiplicity is a general concern when several outcomes, timepoints, or comparisons are tested. Considering many tests without an appropriate plan can increase the chance that at least one result appears notable by chance. This is a general statistical point, not a claim that the trial conducted multiple tests. Because an analysis plan is not reported in the registry record, it is not possible to determine how repeated timepoints or secondary outcomes were handled statistically.

The primary endpoint has scheduled measurements before dosing on Day 1 and on Days 2, 4, 6, 8, 15, 31, 91, and 151 post-dose. Missing-data handling for these measurements is not reported in the registry record. The record does not state whether missing observations were excluded, imputed, or addressed through a model, nor does it report the extent or reasons for missingness. The number contributing measurements at each timepoint is also not reported.

The record defines the pharmacokinetic population and notes that protocol deviations affecting samples could be determined before unblinding. It does not report how many participants were excluded under this definition, which deviations occurred, or whether any sensitivity analyses evaluated the effect of those decisions. Interim analyses, stopping criteria, and a detailed statistical analysis plan are not reported in the registry record. These omissions limit assessment of how analysis choices may affect the reported findings, especially because numerical primary outcome results are not available.

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 0% reporting threshold.

Most frequent non-serious adverse event terms

The registry’s serious adverse event entries report zero affected participants in the nirsevimab group, with 18 at risk, and zero affected participants in the placebo group, with 6 at risk. Deaths are recorded as zero in both groups. These figures describe what is entered in the registry and are not, by themselves, evidence about the cause of any event or the comparative safety of the interventions.

For other adverse events, the registry reports 5 affected participants among 18 at risk in the nirsevimab group and 2 among 6 at risk in the placebo group. The record does not identify the event terms, their severity, timing, duration, or whether participants experienced more than one event. It therefore does not support a detailed comparison of event patterns or an assessment of treatment attribution.

Counts of affected participants are not the same as exposure-adjusted rates, and the record does not give person-time or other exposure-duration information. The safety entries also do not specify how adverse events were collected or whether follow-up was identical across groups. Zero recorded serious adverse events should be read as a count in this study record, not as proof that serious events cannot occur.

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

This trial’s primary question concerns serum concentrations after a single intramuscular dose of nirsevimab in healthy Chinese adults. The record establishes the planned sampling schedule, describes the summary measure as a mean with standard deviation, and defines the pharmacokinetic population. These details clarify the type of evidence the study was designed to collect.

The numerical primary endpoint results are not reported in the registry record. Without those results, it is not possible to describe the concentration profile, estimate a difference between groups, or assess the precision of a comparison. The record’s zero analyses means there are no listed statistical analyses to interpret. This absence does not mean the groups had the same results or that the study demonstrated a null effect.

The primary measure is pharmacokinetic, not a clinical outcome. A serum concentration can describe exposure at a particular sampling time, but it does not by itself establish clinical efficacy or a clinical safety benefit. No relationship between concentration and clinical outcomes is reported in the registry record. The findings therefore cannot be used to state whether nirsevimab does or does not produce a clinical benefit.

The safety entries show zero participants with serious adverse events and zero deaths in both groups, alongside the reported counts for other adverse events. These are descriptive registry counts. They do not establish that treatment caused or prevented an event, and the absence of reported serious events in this study cannot establish absence of risk. The record does not provide event descriptions or exposure-adjusted analyses needed for a fuller safety interpretation.

The intended scope is also limited by the enrolled population: the registry describes healthy Chinese adults. The record does not establish how results would generalize to other populations. In the absence of numerical pharmacokinetic findings, statistical uncertainty measures, and fuller safety details, the appropriate conclusion is about the limits of the report: it documents the study design and selected safety counts but does not provide enough analyzed outcome information to quantify its primary finding.

13. Why This Trial Matters Statistically

This study is statistically informative as an example of why a clearly defined endpoint is not enough to evaluate a trial’s findings. The registry specifies a continuous pharmacokinetic outcome, a summary measure, a population definition, and scheduled serum sampling. Those details make the intended measurement question understandable. Yet without numerical endpoint results or analyses, the magnitude and precision of the finding cannot be assessed.

The distinction between descriptive variation and inferential uncertainty is important in a concentration study. A standard deviation describes variation among measurements, whereas a confidence interval would communicate uncertainty around an estimate. Neither can be interpreted without reported numerical results. The record’s endpoint description indicates which summaries were intended, but does not give values that would allow readers to judge variability or precision.

The scheduled repeated measurements also make analysis choices relevant. Observations at different times from one participant may be related, and the approach used to account for repeated measurements can influence estimates and uncertainty. Because the statistical method is not reported in the registry record, the analytical handling of time cannot be evaluated.

The record also illustrates why planning illustrations must be separated from the study’s own design and results. Its assumptions describe a hypothetical planning exercise based on an observed effect, not a justification for the enrollment target and not observed power. A planning calculation cannot replace a reported estimate and its uncertainty.

Finally, the safety counts show why descriptive event totals need context. The counts identify participants affected, but event terms, timing, exposure duration, and causal attribution are not reported. Overall, the statistical importance of this record lies in the gap between an explicitly described measurement plan and the absence of numerical outcome analyses needed to interpret what the study observed.

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 trial-specific limitation for interpreting the primary endpoint is that numerical serum concentration results are not reported in the registry record. Means, standard deviations, estimates comparing groups, confidence intervals, and p-values are absent. The registry lists zero analyses, so the primary outcome’s magnitude, variability, and precision cannot be assessed.

The record gives a pharmacokinetic population definition but does not report how many participants met it or contributed data at each scheduled timepoint. It does not give a participant flow, exclusions, missing-sample counts, or reasons for missingness. As a result, the relationship between enrollment, safety denominators, and the population contributing to the primary analysis cannot be evaluated from the registry record.

The statistical method used for the repeated serum measurements is not reported. The record does not describe how within-participant correlation, baseline measurements, deviations, or potential outlying values were handled. Nor does it report a detailed statistical analysis plan or sensitivity analyses. These gaps prevent assessment of whether alternative reasonable analysis choices could change the estimated profile or its uncertainty.

The registry reports safety counts but not the event terms for other adverse events, their severity, timing, duration, or treatment attribution. It does not provide exposure-adjusted rates. The absence of serious events in the registry entries should therefore be interpreted as a limited count in the study record, not as a complete characterization of safety.

Generalizability is also bounded by the recorded study population: healthy Chinese adults. The registry record does not establish that the pharmacokinetic or safety findings apply to other populations. The sample-size justification, interim analyses, and fuller protocol details are not reported in the registry record, further limiting evaluation of the study’s planning and conduct.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Evaluate the Pharmacokinetics, Safety, and Tolerability of Nirsevimab in Healthy Chinese Adults — NCT04840849.
• Registry record last updated 2023-11-02; status last verified 2022-12.
• Results first posted 2023-11-02.
• 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

NCT04840849 is a completed Phase 1 randomized, placebo-controlled, parallel-group study of nirsevimab in healthy Chinese adults. The registry describes a single intramuscular dose of nirsevimab compared with a single intramuscular placebo dose. Enrollment was 24; the safety record lists 18 at risk in the nirsevimab group and 6 in the placebo group.

The primary outcome was serum concentration of nirsevimab, summarized as a mean with standard deviation, with sampling scheduled before dosing on Day 1 and on Days 2, 4, 6, 8, 15, 31, 91, and 151 post-dose. The record also lists positive anti-drug antibody as a secondary outcome. It reports zero analyses and does not report numerical primary endpoint results.

Serious adverse events and deaths are recorded as zero in both groups. Other adverse events affected 5 participants in the nirsevimab group and 2 in the placebo group. The registry does not provide event details sufficient for causal interpretation. Thus, the record describes the study’s design, endpoint, and selected safety counts, but does not provide analyzed pharmacokinetic results or their statistical precision.