A Clinical Trial of CSL's 2009 H1N1 Influenza Vaccine (CSL425) in Healthy Children: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for A Clinical Trial of CSL's 2009 H1N1 Influenza Vaccine (CSL425) in Healthy Children (NCT00940108), a randomized phase 2 study. The primary outcome is Haemagglutination Inhibition (HI) Antibody Titre Seroconversion Rate After the First Vaccination.

2. Clinical Question

The study addressed an immune-response question in children, alongside safety and tolerability questions. The primary endpoint was an antibody measure rather than a count of influenza infections or a clinical measure of illness. The posted results therefore describe the frequency of the defined antibody response in each group; they do not by themselves establish how the groups compare on clinical influenza outcomes.

The registry lists 370 participants enrolled. Its primary endpoint is specifically tied to the first vaccination, while the vaccination schedules included a second dose on Day 21. The distinction matters when reading the results: the primary comparison concerns the measured response after dose one, not a response measured after completion of both vaccinations.

3. Trial Design

This was a Phase II, multicentre, randomized, observer-blind study with a parallel-group design. The registry describes masking as quadruple. The study was completed, with a start date of 2009-08 and primary completion in 2009-10. The sponsor is Seqirus.

The study enrolled 370 healthy children aged 6 months to under 9 years. The four result groups were CSL425 (15 mcg) Cohort A, CSL425 (30 mcg) Cohort A, CSL425 (15 mcg) Cohort B, and CSL425 (30 mcg) Cohort B. The intervention descriptions specify 15 mcg in a 0.25 mL injection or 30 mcg in a 0.5 mL injection, given intramuscularly in the deltoid region on Day 0 and Day 21. The registry does not report how participants were allocated among the four groups or what distinguishes Cohort A from Cohort B.

The stated purpose was to evaluate immunogenicity, safety, and tolerability. The primary outcome was HI antibody titre seroconversion after the first vaccination, measured before vaccination and 21 days afterward. Secondary outcomes covered solicited adverse events, including their frequency, intensity, and duration; unsolicited adverse events; serious adverse events; adverse events of special interest; and new onset of chronic illnesses. Five secondary outcomes are posted in the registry, and the record lists 11 outcome measures overall.

All four reported groups received CSL425. The registry results therefore permit comparisons among the listed dose and cohort groups, but do not provide a comparison with placebo or a different vaccine. The trial's original sample-size rationale, allocation details, and fuller protocol description are not reported in the registry record.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Before assignment: One randomized participant withdrew consent prior to vaccine administration and was not included in the participant flow data or in any analysis population.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: The Evaluable Population (for the first vaccination) comprised all randomised participants who received the first study vaccination; provided both pre- and post-vaccination blood samples; were not excluded from analyses (eg, for the use of a prohibited medication or a laboratory-confirmed 2009 H1N1 infection between Visit 1 and Visit 3).

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 Haemagglutination Inhibition (HI) Antibody Titre Seroconversion Rate After the First Vaccination, measured over Before and 21 days after the first vaccination.

The primary endpoint is the percentage of participants who met the registry definition of HI antibody titre seroconversion after the first vaccination. The definition includes either reaching a post-vaccination titre of at least 1:40 from a pre-vaccination titre below 1:10, or having a four-fold or greater increase when the pre-vaccination titre was at least 1:10. The measurement period runs from before vaccination to 21 days after the first vaccination.

This kind of endpoint is used to describe an immune response in a form that can be counted across participants. Reporting the percentage makes the frequency of the defined response comparable across trial groups. The confidence interval describes uncertainty around each group percentage, while a comparison of percentages can express how the observed response rates differ between groups.

As a general statistical point, an antibody endpoint is an immunogenicity measure; it is not the same outcome as infection, symptoms, or another clinical event. The registry's primary endpoint does not report how many participants developed influenza or whether an individual antibody response guarantees protection. Those clinical interpretations cannot be established from seroconversion percentages alone.

The analysis population is described as evaluable for the first vaccination. It includes randomized participants who received that vaccination and had both pre- and post-vaccination blood samples, with some participants excluded from analysis. The record gives examples of possible exclusions, but the complete criteria are not reported in the registry record.

7. Results Posted in the Registry

• CSL425 (30 mcg) Cohort A: 97.3% (71/73) versus 88.2% (67/76) on control; risk difference 9.1 percentage points (95% CI 0.9 to 17.3), risk ratio 1.10 (1.01–1.21); unadjusted two-proportion z-test p = 0.034.
• CSL425 (15 mcg) Cohort B: 85.7% (84/98) versus 88.2% (67/76) on control; risk difference -2.4 percentage points (95% CI -12.5 to 7.6), risk ratio 0.97 (0.87–1.09); unadjusted two-proportion z-test p = 0.637.
• CSL425 (30 mcg) Cohort B: 91.9% (91/99) versus 88.2% (67/76) on control; risk difference 3.8 percentage points (95% CI -5.3 to 12.8), risk ratio 1.04 (0.94–1.15); unadjusted two-proportion z-test p = 0.405.

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is binary at the participant level: each participant either met the seroconversion definition or did not. A group percentage expresses the proportion meeting that definition. The registry reports a percentage and a 95% confidence interval for each of the four groups, alongside the number evaluated in each group. The percentages are 88.2% for CSL425 (15 mcg) Cohort A, 97.3% for CSL425 (30 mcg) Cohort A, 85.7% for CSL425 (15 mcg) Cohort B, and 91.9% for CSL425 (30 mcg) Cohort B.

As a general explanation, a confidence interval gives a range of values reasonably compatible with the observed data under the statistical model used to calculate it. It is not a range containing a fixed share of individual participants, and it does not account for every possible source of uncertainty, such as design limitations or unreported analysis choices. The width of an interval reflects precision: narrower intervals indicate a more precise estimate, while wider intervals leave more uncertainty about the underlying response percentage or group difference.

The registry reports three comparisons, each using CSL425 (15 mcg) Cohort A as the reference. A risk difference is the difference between the two groups' event proportions, expressed on the proportion scale. A value above zero indicates a higher observed response proportion in the compared group; a value below zero indicates a lower one. The reported estimates are 0.091 for CSL425 (30 mcg) Cohort A, -0.024 for CSL425 (15 mcg) Cohort B, and 0.038 for CSL425 (30 mcg) Cohort B. Their confidence intervals are, respectively, 0.009 to 0.173, -0.125 to 0.076, and -0.053 to 0.128.

As a general explanation, a confidence interval for a risk difference that includes zero is compatible with no difference under the interval's assumptions. An interval entirely above or below zero indicates that the corresponding range of differences does not include zero. This is one way to interpret the estimate and its uncertainty; it does not determine the clinical importance of the difference. The first comparison's interval lies above zero, whereas the intervals for the other two comparisons include zero.

The registry also reports risk ratios and odds ratios. A risk ratio compares the group proportions directly as a ratio; a value of 1 represents equal proportions. An odds ratio compares the odds of the outcome, rather than the proportions themselves; a value of 1 represents equal odds. These are general definitions. For CSL425 (30 mcg) Cohort A, the reported risk ratio is 1.103 (95% CI 1.007 to 1.208) and the odds ratio is 4.769 (95% CI 0.994 to 22.88). For CSL425 (15 mcg) Cohort B, the risk ratio is 0.972 (95% CI 0.866 to 1.091) and the odds ratio is 0.806 (95% CI 0.329 to 1.976). For CSL425 (30 mcg) Cohort B, the risk ratio is 1.043 (95% CI 0.943 to 1.153) and the odds ratio is 1.528 (95% CI 0.560 to 4.167). The estimates are not interchangeable: the scales answer related but distinct questions.

Each comparison has an unadjusted p value: 0.034 for CSL425 (30 mcg) Cohort A, 0.637 for CSL425 (15 mcg) Cohort B, and 0.405 for CSL425 (30 mcg) Cohort B. In general, a p value describes how unusual the observed data, or more extreme data, would be under a specified null model. It is not the probability that the null hypothesis is true, and it does not measure the size or importance of an effect. The registry labels these values as unadjusted. The statistical plan, including any adjustment for making multiple comparisons, is not reported in the registry record.

The sizes of the analyzed groups for the primary endpoint were 76 participants for CSL425 (15 mcg) Cohort A, 73 for CSL425 (30 mcg) Cohort A, 98 for CSL425 (15 mcg) Cohort B, and 99 for CSL425 (30 mcg) Cohort B. Those numbers are the evaluable denominators posted for this endpoint; they should not be conflated with the overall enrollment of 370. The record describes an evaluable population requiring receipt of the first vaccination and both blood samples. Its full exclusion criteria and its handling of missing outcome data are not reported in the registry record.

The displayed group percentages and comparisons are unadjusted summaries in the registry. No model-based adjustment for participant characteristics, cohort structure, or other factors is described. The record also does not report the method used to calculate the confidence intervals, the test underlying the p values, or a prespecified hierarchy for the comparisons. Without those details, the estimates can be interpreted on their stated scales, but the precise analysis procedure cannot be reconstructed from the registry record.

As a general concept, statistical significance is not the same as precision, and neither is the same as practical importance. A small p value can accompany an uncertain or modest effect, while a confidence interval makes a range of effect sizes visible. Here, the risk-difference interval for CSL425 (30 mcg) Cohort A is above zero but spans a range of positive values. The other risk-difference intervals span values on both sides of zero. These patterns are more informative than treating a p value alone as a definitive summary.

10. Confidence Intervals and Precision

The group-level confidence intervals convey uncertainty in the observed seroconversion percentages. For CSL425 (15 mcg) Cohort A, the estimate is 88.2%, with a 95% confidence interval from 78.7% to 94.4%. For CSL425 (30 mcg) Cohort A, it is 97.3% (90.5% to 99.7%). For CSL425 (15 mcg) Cohort B, it is 85.7% (77.2% to 92.0%), and for CSL425 (30 mcg) Cohort B, it is 91.9% (84.7% to 96.4%). The ranges overlap, but overlap between separate group intervals is not by itself a formal test of a group difference; the posted comparison intervals address that question more directly.

The risk-difference intervals are particularly useful for reading the comparisons against CSL425 (15 mcg) Cohort A. The estimate for CSL425 (30 mcg) Cohort A is 0.091, with an interval from 0.009 to 0.173. Its lower bound is above zero, while the interval still allows a range of positive differences. For CSL425 (15 mcg) Cohort B, the estimate is -0.024 and its interval runs from -0.125 to 0.076. For CSL425 (30 mcg) Cohort B, the estimate is 0.038 and its interval runs from -0.053 to 0.128. The latter intervals include zero and extend in both directions, indicating uncertainty about the direction as well as the size of the difference.

As a general explanation, confidence intervals are affected by the amount of information in the data and by the variability of the outcome. They do not measure bias, and they do not incorporate uncertainty from design or analysis choices that are not captured by the calculation. The registry record does not report the interval-calculation method, so the intervals are best interpreted as posted rather than reconstructed.

Precision also depends on the chosen measure. The odds-ratio interval for CSL425 (30 mcg) Cohort A, 0.994 to 22.88, is broad compared with its point estimate of 4.769. The risk-ratio interval for that comparison, 1.007 to 1.208, gives a different scale and a different numerical range. For the Cohort B comparisons, the risk-ratio and odds-ratio intervals also include their respective null values of 1. Taken together, the registry offers more precise information about some aspects of the observed response than others; no single interval should be taken as a complete description of uncertainty.

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 planning figures are illustrations based on observed risk differences, not the trial's original design calculations. The original design assumptions, including any sample-size justification, are not reported in the registry record. The posted illustration assumes a two-sided significance level of 0.05, equal allocation between the two compared arms, and a normal approximation. It evaluates effects set at 100%, 75%, or 50% of the observed effect.

For these binary-outcome comparisons, the planning figures are participants per arm. The 80% power column means the per-arm sample size estimated to give an 80% chance of detecting the specified effect under the stated assumptions; the 90% power column uses a higher chance of detection and therefore generally requires more participants. These are hypothetical planning targets, not counts of participants in the trial. The figures are not observed power.

The calculations are comparison-specific because the observed risk difference differs across the three comparisons. For example, using 100% of the observed effect gives 127 participants per arm for 80% power and 170 participants per arm for 90% power for the CSL425 (30 mcg) Cohort A comparison. For CSL425 (15 mcg) Cohort B, the corresponding figures are 2,985 and 3,995 participants per arm; for CSL425 (30 mcg) Cohort B, they are 995 and 1,331 participants per arm.

Within each comparison, the planning figures increase when the target is reduced to 75% or 50% of the observed effect. This follows from a general statistical principle: smaller effects are harder to distinguish from random variation, so detecting them with the same power generally requires more participants. The illustrations therefore show how strongly planning needs can depend on the assumed effect size. They should not be interpreted as evidence that the trial was designed or powered using these assumptions.

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 = 0.882; treatment proportion p₁ = 0.973; average p̄ = 0.927.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.3677 = 0.7206.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.3620 = 0.3047.
4. n = (0.7206 + 0.3047)² / (0.0910)² = 126.9, rounded up to 127 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 <- 0.881578947368421                          # control proportion
p1 <- 0.972602739726027                          # 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(940108)
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 = 127 (80% power), 170 (90% power)
 75% of observed effect: n per arm = 259 (80% power), 346 (90% power)
 50% of observed effect: n per arm = 655 (80% power), 876 (90% power)
power.prop.test: 126.9 
Simulated power at n = 127 per arm: 0.831 (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. Multiplicity, Missing Data and Analysis Populations

The registry lists 11 outcome measures overall and posts five secondary outcomes. The primary endpoint is the first-vaccination seroconversion rate. Secondary outcomes concern solicited adverse events after either vaccination, duration of solicited events after each vaccination, serious adverse events, adverse events of special interest, new onset of chronic illnesses, and unsolicited adverse events. Considering several outcomes and comparisons raises a general multiplicity issue: when many statistical questions are assessed, the chance of at least one apparently notable result can increase. The registry does not report a multiplicity adjustment, a testing hierarchy, or a statistical analysis plan.

The three posted risk-difference comparisons use CSL425 (15 mcg) Cohort A as the reference, and their p values are unadjusted. The record does not explain whether these comparisons were prespecified, whether other comparisons were planned, or how any family of analyses was to be interpreted. Consequently, the p value of 0.034 should be understood as an individual unadjusted comparison rather than as an adjusted conclusion across outcomes and groups.

The endpoint population is described as the evaluable population for the first vaccination. Participants had to be randomized, receive the first study vaccination, and provide both pre- and post-vaccination blood samples. Participants could also be excluded for reasons such as prohibited medication use or a laboratory-confirmed 2009 H1N1 infection, but the remaining text of that criterion is incomplete in the registry record. The complete exclusion rules are not reported in the registry record.

The primary endpoint denominators are 76, 73, 98, and 99 across the four listed groups. The registry does not describe how missing blood samples or other missing outcome information were handled, whether imputation was used, or how participants excluded from the evaluable population were treated in any other analysis. It also does not report a separate analysis population definition for the safety outcomes. These omissions limit assessment of how missingness or exclusions may affect the estimates.

The record lists 0 analyses as separate registry analysis entries. This does not supply the missing analysis plan or resolve which methods were used to obtain the posted comparisons. Details of covariate adjustment, subgroup analysis, interim analyses, and multiplicity handling are not reported in the registry record.

14. 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 2% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: convulsion (2.4%), kawasaki's disease (1.2%), gastroenteritis viral (1.2%), asthma (1.2%), lobar pneumonia (1.0%).

The registry posts serious adverse event counts and other adverse event counts for each group. For CSL425 (15 mcg) Cohort A, 4 of 82 participants at risk were affected by a serious adverse event, and 81 of 82 were affected by another adverse event. For CSL425 (30 mcg) Cohort A, the corresponding counts were 1 of 80 and 78 of 80. For CSL425 (15 mcg) Cohort B, they were 1 of 103 and 91 of 103; for CSL425 (30 mcg) Cohort B, they were 1 of 104 and 96 of 104.

These figures count affected participants, not necessarily the total number of individual event episodes. The registry also lists serious-event terms and percentages, including Convulsion at 2.4%, Kawasaki's disease at 1.2%, Gastroenteritis viral at 1.2%, Asthma at 1.2%, Lobar pneumonia at 1.0%, and Pyrexia at 1.0%. The record does not provide enough context in these entries to infer that any event was caused by the vaccine or to compare event risk fully across groups. Death counts are not reported in the registry record.

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

The results describe antibody seroconversion after the first vaccination among the evaluable participants in each group. The observed percentages range from 85.7% to 97.3%, with confidence intervals that show uncertainty around each estimate. The reported risk-difference comparison for CSL425 (30 mcg) Cohort A is positive and its confidence interval does not include zero. The two Cohort B comparisons have intervals that include zero, leaving uncertainty about the direction and size of their differences from the reference group.

These findings do not, on their own, establish that one dose level is superior across cohorts. The comparison pattern is not uniform, and the registry does not explain the cohort structure or report an adjusted analysis combining cohort information. The p values are unadjusted, and the record does not report how multiplicity was handled. The estimates should therefore be read as specific descriptive and inferential results for the posted comparisons.

The primary outcome measures an antibody response, not the occurrence of influenza disease. A high seroconversion percentage is evidence about the stated laboratory endpoint in this study population; it is not a direct count of infections, symptoms, hospitalization, or other clinical outcomes. The registry record does not establish that a participant meeting the antibody definition was protected from infection.

The safety entries show that adverse events were recorded, including serious adverse events in each group. Counts alone do not establish causation, severity beyond the registry classifications, or comparative safety. The registry's listed secondary outcomes include event intensity and duration, but the full outcome results and detailed analysis information are not reported in the registry record.

The most defensible reading is limited to what the registry reports: group-specific response percentages, intervals, unadjusted comparisons, and adverse-event counts for the posted populations and timeframes. Interpretation beyond these endpoints requires information that is not reported in the registry record, including the complete analysis plan, the full population rules, and clinical outcome results.

16. Why This Trial Matters Statistically

This trial illustrates why an immunogenicity result needs to be read on both the group and comparison scales. The group percentages are all relatively high, yet the estimated differences versus CSL425 (15 mcg) Cohort A vary in direction and precision. A percentage alone cannot answer whether groups differ; the effect estimate and its confidence interval provide information about the size and uncertainty of that comparison.

It also demonstrates how the choice of statistical measure affects interpretation. Risk differences express a contrast in proportions, while risk ratios and odds ratios use ratio scales. Their numerical values can look quite different, particularly for a common binary outcome. Reading all estimates as if they were the same quantity can distort the size of the observed contrast.

The record highlights the distinction between an unadjusted comparison and a complete analysis strategy. One unadjusted comparison has a confidence interval above zero, while the others include zero. Without a reported multiplicity plan, prespecified testing hierarchy, or full statistical methods, these findings cannot be treated as a comprehensive account of all testing in the study.

Finally, the study connects efficacy-style statistical interpretation with safety reporting. The primary endpoint concerns an antibody response after the first vaccination, while adverse-event counts concern different outcomes and populations. Neither an antibody response nor a simple safety count replaces the other. Separating endpoints, denominators, timeframes, and estimands is central to sound interpretation of clinical trial results.

17. 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.
• Participant counts were reconstructed from posted percentages and arm sizes, so small rounding differences are possible.

The primary endpoint is an antibody seroconversion measure after the first vaccination. The registry does not post a clinical influenza outcome alongside this primary result, so the reported response percentages do not quantify illness prevention. The primary observation window is before vaccination and 21 days after the first vaccination; the registry's primary result therefore does not describe a later antibody response after the second vaccination.

All reported groups received CSL425, at either 15 mcg or 30 mcg. There is no placebo or alternative vaccine group among the posted arms, limiting the comparisons to the listed dose and cohort groups. The record does not explain the distinction between Cohort A and Cohort B or the allocation across groups. This makes it difficult to know whether cohort differences reflect design features relevant to interpretation.

The analysis is based on an evaluable population requiring receipt of the first vaccination and both blood samples. Complete exclusion criteria and the handling of missing data are not reported in the registry record. The endpoint denominators are smaller than the overall enrollment, but the record does not provide enough detail to assess how exclusions or missing measurements may have affected results.

The registry posts unadjusted comparison p values and does not report a multiplicity strategy, analysis plan, or detailed statistical methods. The reported safety counts are not accompanied by complete event-level context in these entries; death counts are not reported in the registry record. The full results for all listed secondary outcomes, including intensity and duration details, are also not reported in the registry record. These limitations constrain conclusions about both comparative immunogenicity and safety.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: A Clinical Trial of CSL's 2009 H1N1 Influenza Vaccine (CSL425) in Healthy Children — NCT00940108.
• Registry record last updated 2018-06-28; status last verified 2018-04.
• Results first posted 2013-11-20.
• 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.

21. Record Summary

NCT00940108 is a completed, randomized, quadruple-masked, parallel-group Phase II study of CSL425 in healthy children aged 6 months to under 9 years. The registry lists 370 participants enrolled. The two vaccine doses were 15 mcg and 30 mcg, administered on Day 0 and Day 21.

The primary outcome was HI antibody titre seroconversion after the first vaccination. Reported group percentages ranged from 85.7% to 97.3%. Three comparisons used CSL425 (15 mcg) Cohort A as the reference; one risk-difference interval was entirely above zero, and two included zero. The p values are unadjusted.

Posted safety data include serious and other adverse-event counts. The original sample-size rationale, full analysis plan, complete exclusion criteria, missing-data methods, and multiplicity handling are not reported in the registry record.