Safety, Tolerability and Prophylactic Antiviral Activity of Neumifil Against Influenza Via a Human Viral Challenge Model: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Safety, Tolerability and Prophylactic Antiviral Activity of Neumifil Against Influenza Via a Human Viral Challenge Model (NCT05507567), a randomized phase 2 study. The primary outcome is Incidence of Symptomatic Influenza Infection.

2. Clinical Question

3. Trial Design

The registry record describes a randomized, double-blind, parallel, placebo-controlled Phase 2a study sponsored by Pneumagen Ltd. It is titled as a study of the safety, tolerability, and prophylactic antiviral activity of Neumifil against influenza using a human viral challenge model. The record lists 104 participants enrolled and a completed study status.

Participants were assigned to multiple-dose Neumifil, single-dose Neumifil, or placebo. The multiple-dose group received 3 single daily intranasal doses before challenge. In the single-dose group, a single Neumifil administration was blinded by two single daily placebo administrations; all doses were completed before challenge. The placebo group received 3 single daily intranasal doses before challenge. The registry record identifies the study population as healthy adults.

The listed study start was 2022-08-12, and primary completion was 2023-05-04. The primary endpoint analysis used a Per Protocol population, defined in the record as participants who received all doses and challenge virus and completed quarantine up to Day 8. Its group sizes were 30 for multiple-dose Neumifil, 29 for single-dose Neumifil, and 40 for placebo. The pooled Neumifil group contained 59 participants.

The study also listed secondary outcomes covering total symptom score over time, viral shedding over time, nasal discharge, and solicited and unsolicited adverse events. There were 9 outcome measures and 5 analyses recorded overall. The registry record does not report the original design assumptions or a justification for the planned enrollment.

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.

Randomised and Received Challenge Virus

Reasons for not completing this period:

From Challenge Virus to End of Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Per Protocol population (participants who received all doses, challenge virus and completed quarantine up to Day 8)

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 Incidence of Symptomatic Influenza Infection, measured over Day 1 to Day 8.

The primary endpoint was the incidence of symptomatic influenza infection, expressed as the number of participants meeting a combined virologic and symptom definition during Day 1 to Day 8. A participant counted as having an event if viral shedding measured by RT-qPCR was quantifiable on 2 consecutive days and any one of 11 assessed symptoms reached grade 2 or greater at a single time point.

Symptoms were graded from 0 to 3. Grade 0 meant no symptoms; grade 1 meant just noticeable; grade 2 meant clearly bothersome from time to time but not interfering with normal daily activities; and grade 3 meant quite bothersome most or all of the time and preventing participation in activities. Thus, the endpoint did not count viral detection alone or mild symptoms alone: both the stated shedding pattern and the symptom threshold were required.

General: A combined endpoint can capture more than one aspect of an illness—in this case, laboratory evidence of viral shedding and a symptom criterion. It can also make the result depend on each component's measurement and on how the combined case definition is applied. The registry record does not report additional detail about endpoint adjudication or the handling of measurements that could not be evaluated.

The endpoint was used to compare the proportions of participants meeting that definition across randomized groups. It is a binary participant-level outcome: each participant either met the event definition or did not. The registry record's primary analysis population was Per Protocol rather than all enrolled participants.

7. Results Posted in the Registry

• Neumifil Multiple Dose Prophylactic Treatment: 20.0% (6/30) versus 40.0% (16/40) on control; risk difference -20.0 percentage points (95% CI -40.9 to 0.9), risk ratio 0.50 (0.22–1.12); unadjusted two-proportion z-test p = 0.074.
• Neumifil Single Dose Prophylactic Treatment: 20.7% (6/29) versus 40.0% (16/40) on control; risk difference -19.3 percentage points (95% CI -40.5 to 1.9), risk ratio 0.52 (0.23–1.16); unadjusted two-proportion z-test p = 0.089.
• Pooled Neumifil Groups: 20.3% (12/59) versus 40.0% (16/40) on control; risk difference -19.7 percentage points (95% CI -38.0 to -1.3), risk ratio 0.51 (0.27–0.96); unadjusted two-proportion z-test p = 0.033.

8. Statistical Interpretation

9. Statistical Methods Explained

The primary endpoint is binary at the participant level: participants either meet the stated symptomatic-infection definition or do not. The posted data give the event count and denominator for each group. A risk difference expresses the difference between the two event proportions in the compared groups. In these recalculations, a negative value means the observed event proportion was lower in the Neumifil group than in placebo. General: unlike a relative measure, a risk difference stays on the event-proportion scale, which can make the size and direction of the contrast straightforward to describe.

The comparisons also include risk ratios and odds ratios with confidence intervals. General: a risk ratio compares event proportions as a ratio, while an odds ratio compares event odds. These relative measures use different scales from the risk difference, so their numeric values should not be interpreted as interchangeable. All three measures describe the same posted binary outcome, but each frames the contrast differently. The registry's reported analysis for the pooled comparison is a chi-squared test; it reports a p-value but no test statistic or confidence interval.

What does a confidence interval add?

General: a confidence interval represents the range of values compatible with the data and the method used, at the stated confidence level. It communicates uncertainty about the estimated contrast rather than only giving a single point estimate. For the recalculated risk differences, intervals that include zero allow for no difference as one of the values compatible with the data. The registry's sponsor analysis does not include a confidence interval in the posted record, so that precision cannot be assessed from its reported test alone.

How should the p-values be read?

General: a p-value describes how unusual data at least as incompatible with a specified null model would be if that model and the test assumptions were true. It is not the probability that the null hypothesis is true, nor does it measure the size or clinical importance of an effect. Here, the recalculated unadjusted p-values accompany the recalculated risk differences. The sponsor's reported p-value for the pooled comparison comes from a chi-squared analysis. Because the registry record flags a discrepancy, the sponsor's own analysis takes precedence for that comparison.

Why can low event counts affect estimates?

General: when event counts are limited, estimates can be sensitive to the outcomes of individual participants, and uncertainty may be substantial. The confidence intervals for the separate regimen comparisons are wide enough to include both zero and risk differences in the opposite direction from the point estimate. This is a reason to consider the interval alongside the point estimate and p-value, rather than treating a single threshold as a complete summary.

What does the analysis population mean?

The primary endpoint is reported for the Per Protocol population, defined as participants who received all doses and challenge virus and completed quarantine up to Day 8. This is distinct from the enrollment count. General: an analysis restricted to participants meeting protocol-completion criteria can answer a different question from an analysis of all randomized participants, and the choice can affect results if exclusions or missing observations are related to outcome. The registry record does not report the number or reasons for any exclusions from the primary endpoint population or an all-randomized analysis of this endpoint.

For the pooled comparison, the posted recalculation combines the Neumifil groups and compares them with placebo. Pooling increases the number of participants represented in the Neumifil comparison, but it also treats the two regimens as a combined group. It cannot establish that the regimen-specific effects are equivalent. No formal comparison between the two Neumifil groups is reported in the registry record.

General: if outcome variability exceeds what a statistical model assumes, a model may understate uncertainty; this is often called over-dispersion. The primary endpoint is a binary count, and the registry record does not report a model-based over-dispersion assessment. The posted recalculations are unadjusted comparisons from summary statistics, not a substitute for an unreported prespecified model or analysis plan. The registry record does not report the trial's original statistical methods in enough detail to determine whether other adjustments or sensitivity analyses were planned.

10. Confidence Intervals and Precision

The confidence intervals indicate substantial uncertainty around the risk-difference estimates. For multiple-dose Neumifil versus placebo, the recalculated risk difference is -0.2, with a 95% confidence interval from -0.409 to 0.009. For single-dose Neumifil versus placebo, it is -0.193, with a 95% confidence interval from -0.405 to 0.018. Both intervals include zero and extend to positive values, so the data are compatible with no difference and with a difference favoring placebo on this scale, as well as with a negative risk difference.

The pooled Neumifil comparison has a recalculated risk difference of -0.197 and a 95% confidence interval from -0.380 to -0.013. That interval remains below zero, but its range is still broad. The point estimate is not a precise statement of the underlying effect; the interval communicates the uncertainty associated with the posted counts and the recalculation method.

General: confidence intervals describe statistical uncertainty under the method's assumptions. They do not include every source of uncertainty, such as uncertainty about whether the endpoint definition captures outcomes of interest or whether results apply beyond the study setting. The registry record reports a p-value of 0.033 for the sponsor's pooled chi-squared analysis but no confidence interval for that analysis. The recalculated interval should therefore not be presented as the sponsor's interval.

These intervals are unadjusted recalculations, and the registry record does not report whether multiplicity was addressed. That distinction matters when interpreting several comparisons or outcomes together: intervals and p-values from separate analyses do not automatically account for the number of questions asked. The record also does not report an interval for the difference between the two Neumifil regimens.

11. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The sample-size figures are planning illustrations based on the observed effect, not the original trial's design calculations. The registry record does not report the trial's own sample-size assumptions or justification. The figures for this binary endpoint are participants per arm, not total events. The planning assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation; the effect to detect is the stated fraction of the observed effect.

The columns for 80% power and 90% power describe the number of participants per arm under those assumptions for a study designed to detect the specified effect. General: power is the probability of detecting an effect of the assumed size under the specified model and testing conditions, if that effect is present. The figures are planning quantities, not counts observed in this trial.

The rows use 100% of the observed effect, 75% of the observed effect, and 50% of the observed effect. For example, the pooled comparison's planning illustration lists 85 participants per arm for 80% power and 113 participants per arm for 90% power at 100% of the observed effect. At 75% of the observed effect, it lists 158 participants per arm for 80% power and 211 participants per arm for 90% power. At 50% of the observed effect, it lists 369 participants per arm for 80% power and 494 participants per arm for 90% power. Smaller effects require more participants under these assumptions.

These illustrations are not observed power. They do not show the probability that the completed trial detected a true effect, and they should not be used to reinterpret the trial's results as if a prospective design calculation had been reported. The original design assumptions are not reported in the registry record.

12. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, p₀ and p₁ are the control and treatment proportions, and p̄ is their average.

Worked calculation for this trial

1. Control proportion p₀ = 0.400; treatment proportion p₁ = 0.200; average p̄ = 0.300.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.6481 = 1.2702.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.6325 = 0.5323.
4. n = (1.2702 + 0.5323)² / (-0.2000)² = 81.2, rounded up to 82 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
p0 <- 0.4                          # control proportion
p1 <- 0.2                          # treatment proportion
n_per_arm <- function(power, frac = 1) {
  q1 <- p0 + (p1 - p0) * frac               # smaller effect = fraction of the observed difference
  pbar <- (p0 + q1) / 2
  z_b <- qnorm(power)
  ceiling(round((z_a * sqrt(2 * pbar * (1 - pbar)) + z_b * sqrt(p0 * (1 - p0) + q1 * (1 - q1)))^2 / (q1 - p0)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (unrounded n per arm)
cat("power.prop.test:", round(power.prop.test(p1 = p0, p2 = p1, power = 0.80)$n, 1), "\n")

# Simulation: how often does the z-test reject at the 80%-power sample size?
set.seed(5507567)
n    <- n_per_arm(0.80)
reps <- 20000
x0 <- rbinom(reps, n, p0); x1 <- rbinom(reps, n, p1)
ph <- (x0 + x1) / (2 * n)
z  <- ((x1 - x0) / n) / sqrt(ph * (1 - ph) * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(z) > z_a, na.rm = TRUE), reps))

Output from running the code

100% of observed effect: n per arm = 82 (80% power), 109 (90% power)
 75% of observed effect: n per arm = 152 (80% power), 203 (90% power)
 50% of observed effect: n per arm = 356 (80% power), 477 (90% power)
power.prop.test: 81.2 
Simulated power at n = 82 per arm: 0.810 (20000 replicates)

The simulation draws many pairs of event counts at the planned sample size and counts how often the two-proportion z-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

13. Analyses Reported by the Sponsor

The registry record reports the sponsor's pooled comparison of placebo and pooled Neumifil using a chi-squared analysis, with p = 0.033. The recalculated unadjusted comparison gives a risk difference of -0.197, a 95% confidence interval from -0.380 to -0.013, and p = 0.033. These are not identical results: the recalculation is a simple unadjusted analysis from the posted summary statistics, while the registry's stated result is the sponsor's own chi-squared analysis.

The record flags a discrepancy between the posted sponsor result and the recalculation. The sponsor's own analysis takes precedence. The recalculated estimate and interval can still help describe the observed contrast and its precision, but they should not replace the sponsor's reported test result. The registry record does not report a confidence interval for the sponsor's chi-squared analysis or additional details that explain the discrepancy.

The multiple-dose and single-dose recalculations are also unadjusted comparisons with placebo; their p-values are 0.074 and 0.089, respectively. The reported sponsor analysis listed in the registry record is for the pooled comparison, not separate sponsor tests for each regimen. No sponsor analysis directly comparing the two Neumifil regimens is reported in the registry record.

14. Multiplicity, Missing Data and Analysis Populations

The registry record lists a primary endpoint and several secondary outcomes, including total symptom score over time, viral shedding over time, weight of nasal discharge, nasal discharge, and solicited and unsolicited adverse events. It records 9 outcome measures, 7 secondary outcomes posted, and 5 analyses. The secondary outcome list repeats viral shedding over time. These details indicate that the study considered more than one outcome, but they do not establish how many hypotheses were tested or how those tests were organized.

The registry record does not report whether the sponsor adjusted for multiple comparisons, used a testing hierarchy, or designated particular analyses as confirmatory or exploratory. Without that information, the posted p-values should be read as the results of their individual analyses, not as evidence that any family-wise error or false-discovery procedure was applied. The recalculated p-values are explicitly unadjusted.

The primary endpoint is reported in the Per Protocol population. The record defines that population as participants who received all doses and challenge virus and completed quarantine up to Day 8. It does not report the number excluded from this population, reasons for exclusion, the amount or pattern of missing endpoint data, or a missing-data method. It also does not report an intention-to-treat analysis for the primary endpoint. Consequently, the posted endpoint counts cannot establish how a different analysis population or missing-data approach would have affected the estimates.

The record does not report the original statistical analysis plan, including details of model selection, covariate adjustment, sensitivity analyses, or interim analyses. Those matters should not be inferred from the posted count data or from the sponsor's chi-squared p-value. The reported group sizes and comparisons support a description of the posted results, but not a reconstruction of unreported analysis procedures.

15. 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 serious adverse event figures are reported for safety groups of 32 participants in the multiple-dose Neumifil group, 31 in the single-dose group, and 41 in the placebo group. The record lists 0 serious adverse events in each group and 0 deaths in each group. These are the posted counts for participants at risk in the safety summaries.

The safety denominators differ from the primary endpoint Per Protocol group sizes of 30, 29, and 40. The registry record does not explain the difference in these populations or provide further participant-flow detail. The serious adverse event figures should therefore be read using their stated safety denominators, not the primary endpoint denominators.

The registry record also lists participants affected by other, non-serious adverse events: 30 in the multiple-dose group, 25 in the single-dose group, and 34 in the placebo group. These counts are distinct from the serious adverse event counts. No serious adverse event terms are listed among the top serious terms. The record does not provide event-level details or establish whether the groups differed in severity or type of non-serious events.

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

The posted primary endpoint results show that fewer participants met the symptomatic-infection definition in each Neumifil group than in placebo: 6 of 30 with multiple-dose treatment, 6 of 29 with single-dose treatment, and 16 of 40 with placebo. The pooled group had 12 events among 59 participants. These counts describe the Per Protocol population in this human challenge study.

The recalculated risk-difference estimates are negative for each comparison with placebo. The separate regimen confidence intervals include zero, while the pooled recalculated interval does not. The sponsor's reported pooled chi-squared p-value is 0.033; because the record flags a discrepancy with the recalculation, the sponsor's own analysis takes precedence. These statistical results do not establish that the observed contrast will recur in another study, nor do they demonstrate the size or certainty of an effect beyond the specific endpoint and population studied.

The result is tied to a particular case definition: quantifiable viral shedding on 2 consecutive days together with a symptom of grade 2 or greater at a single time point. A different endpoint definition could capture a different aspect of infection or symptoms. The study involved healthy adults in a controlled viral challenge model, and the results should not be assumed to describe other populations or settings.

The pooled result combines participants receiving two different Neumifil regimens. It cannot answer whether the regimens have equivalent effects. The registry record does not report a direct comparison between them, nor does it report whether the statistical plan accounted for multiple comparisons. The endpoint was analyzed in a Per Protocol group rather than all enrolled participants, and information on exclusions and missing outcomes is not reported in the registry record.

Accordingly, the posted data support a descriptive account of event counts and statistical uncertainty in this trial. They do not, on their own, provide a complete account of treatment effects, long-term outcomes, or safety beyond the adverse event summaries recorded.

17. Why This Trial Matters Statistically

This trial illustrates how a clinical question can depend on a deliberately combined endpoint. The primary outcome required both a specified pattern of viral shedding and a symptom threshold. That definition makes clear what counted as symptomatic infection, but it also means that interpretation depends on the measurement of both components and on their combination.

The posted results also show why point estimates, confidence intervals, and p-values answer related but different questions. The risk-difference estimates describe the direction and scale of the observed contrasts. The intervals communicate precision, and the p-values summarize compatibility with a null model under the relevant test assumptions. For the two regimen-specific recalculations, the intervals include zero; for the pooled recalculation, the interval does not. The sponsor's pooled analysis is reported separately and takes precedence because the record flags a discrepancy.

Pooling can be useful for presenting a combined comparison, but it changes the question: it does not establish that the single-dose and multiple-dose regimens have the same effect. This matters statistically because a pooled estimate can conceal differences between the component groups. The registry record does not report a direct regimen-to-regimen analysis.

The study also highlights the importance of distinguishing enrollment, analysis populations, and safety denominators. The record lists 104 enrolled participants, a Per Protocol population for the primary endpoint, and different safety group denominators. Without participant-flow and missing-data details, readers cannot fully reconstruct how those populations relate.

Finally, planning illustrations based on observed effects are not a substitute for the trial's original design justification. They can show how sample-size requirements change when planning around smaller effects, but the original design assumptions are not reported in the registry record. Keeping that distinction clear helps prevent retrospective planning figures from being mistaken for evidence about the trial's prospective design or its probability of success.

18. 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 primary endpoint analysis is limited to the Per Protocol population, defined as participants who received all doses and challenge virus and completed quarantine up to Day 8. Although the record lists enrollment of 104, it does not report participant flow or explain the difference between enrollment, primary endpoint group sizes, and safety denominators. Reasons for any exclusions are not reported in the registry record.

The endpoint combines RT-qPCR viral shedding and symptom scores. It requires quantifiable shedding on 2 consecutive days and at least one symptom at grade 2 or greater at a single time point. The registry record does not report further information on endpoint adjudication, missing measurements, or whether alternative endpoint definitions were examined.

The study used a human viral challenge model in healthy adult participants. This setting is distinct from other populations and circumstances, so the posted results should be interpreted within the study's defined population and challenge conditions. Details about broader applicability are not reported in the registry record.

The registry record does not report the original statistical analysis plan, the trial's sample-size justification, multiplicity procedures, or details of any interim analyses. It also does not report an intention-to-treat analysis, reasons for missing outcome data, or sensitivity analyses addressing missingness. These omissions limit assessment of how robust the primary results are to alternative analysis choices.

The sponsor's pooled chi-squared result and the simple recalculation are flagged as discrepant. The sponsor's own analysis takes precedence, but the registry record does not provide enough detail to explain the difference or report a confidence interval for that analysis. No direct comparison between the two Neumifil regimens is reported.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Safety, Tolerability and Prophylactic Antiviral Activity of Neumifil Against Influenza Via a Human Viral Challenge Model — NCT05507567.
• Registry record last updated 2024-10-28; status last verified 2024-10.
• Results first posted 2024-10-28.
• 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.

22. Record Summary

The registry record describes a completed, randomized, double-blind, parallel, placebo-controlled Phase 2a human influenza challenge study sponsored by Pneumagen Ltd. It lists 104 participants enrolled, a study start of 2022-08-12, and primary completion on 2023-05-04.

The primary endpoint was symptomatic influenza infection from Day 1 to Day 8, defined by quantifiable viral shedding on 2 consecutive days and a symptom score of grade 2 or greater at a single time point. The Per Protocol analysis recorded 6 events among 30 participants in the multiple-dose group, 6 among 29 in the single-dose group, and 16 among 40 in placebo. The pooled Neumifil group recorded 12 events among 59 participants.

The registry reports a sponsor chi-squared p-value of 0.033 for the pooled comparison. A discrepancy with the unadjusted recalculation is flagged, so the sponsor's own analysis takes precedence. Serious adverse events and deaths were recorded as 0 in each safety group.