Persistence of Antibodies at 3, 4 and 6 Years of Age After Vaccination With Meningococcal, Pneumococcal and Hib Vaccines: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Persistence of Antibodies at 3, 4 and 6 Years of Age After Vaccination With Meningococcal, Pneumococcal and Hib Vaccines (NCT00891176), a randomized phase 3 study. The primary outcome is Number of Subjects With Meningococcal Serogroup C Serum Bactericidal Titers Using Rabbit Complement (rSBA-MenC) Equal to or Above Cut-off Value.

2. Clinical Question

3. Trial Design

This was a randomized, open-label, parallel-group phase 3 study with 582 participants enrolled. The registry lists the study as completed, with a start date of 2009-05-14 and primary completion on 2012-11-21. These dates describe the registry record; they do not add details about the conduct of each visit or the timing of every measurement.

The record describes this trial as an extension phase focused on persistence of pneumococcal, meningococcal serogroup C, Hib and hepatitis B antibodies when children were aged 3, 4 and 6 years. No vaccine was administered during the persistence phase. The courses received before this phase varied among the four groups. The group names identify combinations of pneumococcal and meningococcal vaccines; their descriptions also refer to other vaccines received in the primary study.

The primary study and booster study are distinct from this extension and have separate registry postings. The persistence analysis therefore concerns antibody measurements after those earlier courses, rather than a new randomized vaccination delivered during this trial phase. The available description identifies an According-to-Protocol cohort for the primary outcome at age 3, based on evaluability, completion of the full earlier vaccination course and availability of an age-3 result.

Random allocation is stated in the registry, but the method used to generate or conceal the allocation is not reported in the registry record. Masking is listed as none. The registry record does not report the original sample-size justification, the planned statistical model, any interim analyses or details of the randomization procedure. Those omissions limit how fully the design can be reconstructed from the posting alone.

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: At 3 years of age, 582 subjects were enrolled. One subject who did not participate in the primary study was enrolled by mistake and was therefore withdrawn from the study. Therefore the total number of subjects participating at the 36 months of age time point was 581.

At 3 Years of Age

At 4 Years of Age

At 6 Years of Age

Analysis population for the primary outcome, as defined in the registry: Analysis was performed on the According-to-Protocol cohort for antibody persistence at 3 years of age, which included all evaluable subjects who had received the full vaccination course in the primary study (NCT00334334) and in the booster study (NCT00463437) and had available results at 3 years of age.

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

6. Primary Endpoint

The registry lists the primary outcome as Number of Subjects With Meningococcal Serogroup C Serum Bactericidal Titers Using Rabbit Complement (rSBA-MenC) Equal to or Above Cut-off Value, measured over At 3 years of age.

The primary endpoint counts subjects whose serum bactericidal antibody titer against meningococcal serogroup C, measured using rabbit complement (rSBA-MenC), was at or above the cut-off of 1:8 at 3 years of age. It is a binary outcome: each child’s result is classified according to whether the measured titer reaches the threshold. The endpoint description states that the age-3 and age-4 samples were tested at a GSK laboratory, while the age-6 assay was performed at the Public Health England laboratory.

General statistical explanation: a threshold endpoint can make group results easier to summarize as counts above and below a defined level. It also discards information about how far a titer lies from that threshold. Two children with different measured titers may receive the same classification if both are on the same side of the cut-off. The endpoint is therefore useful for describing the proportion meeting a specified antibody criterion, but it does not show every feature of antibody levels.

The endpoint measures an antibody assay result, not a clinical illness outcome. The registry record does not establish that crossing this cut-off guarantees protection in an individual child, nor does it report a clinical disease endpoint for this primary measure.

7. Results Posted in the Registry

• Synflorix-NeisVac-C Group: 98.6% (144/146) versus 86.3% (120/139) on control; risk difference 12.3 percentage points (95% CI 6.3 to 18.3), risk ratio 1.14 (1.07–1.22); unadjusted two-proportion z-test p = <0.001.
• Synflorix-Menitorix Group: 88.8% (127/143) versus 86.3% (120/139) on control; risk difference 2.5 percentage points (95% CI -5.2 to 10.2), risk ratio 1.03 (0.94–1.12); unadjusted two-proportion z-test p = 0.528.
• Prevenar-Menitorix Group: 82.5% (113/137) versus 86.3% (120/139) on control; risk difference -3.8 percentage points (95% CI -12.4 to 4.7), risk ratio 0.96 (0.86–1.06); unadjusted two-proportion z-test p = 0.378.

8. Secondary Efficacy Endpoints

The registry also posts results for secondary outcomes. For each outcome below, the endpoint type, the test applied to the posted summary statistics, the result and its interpretation are given in turn. Secondary endpoints are usually not adjusted for multiple testing, so they support rather than confirm the primary finding.

Number of Subjects With an rSBA-MenC Titer Equal to or Above Cut-off Value

• Endpoint type: Binary: the number of participants with the event, compared as proportions.
• Test: Unadjusted two-proportion z-test, with a Wald 95% confidence interval for the risk difference.
• Result:
  • Synflorix-NeisVac-C Group: 74.7% (109/146) versus 49.6% (69/139) on control; risk difference 25.0 percentage points (95% CI 14.1 to 35.9), risk ratio 1.50 (1.24–1.82); unadjusted two-proportion z-test p = <0.001.
  • Synflorix-Menitorix Group: 68.5% (98/143) versus 49.6% (69/139) on control; risk difference 18.9 percentage points (95% CI 7.6 to 30.2), risk ratio 1.38 (1.13–1.69); unadjusted two-proportion z-test p = 0.001.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the proportion with the event is statistically higher for Synflorix-NeisVac-C Group than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.
  • The 95% confidence interval excludes no difference, so the proportion with the event is statistically higher for Synflorix-Menitorix Group than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

Number of Subjects With rSBA-MenC Titer Equal to or Above Cut-off Value

• Endpoint type: Binary: the number of participants with the event, compared as proportions.
• Test: Unadjusted two-proportion z-test, with a Wald 95% confidence interval for the risk difference.
• Result:
  • Synflorix-NeisVac-C Group: 13.9% (19/137) versus 8.6% (11/128) on control; risk difference 5.3 percentage points (95% CI -2.3 to 12.8), risk ratio 1.61 (0.80–3.26); unadjusted two-proportion z-test p = 0.176.
  • Synflorix-Menitorix Group: 11.5% (15/130) versus 8.6% (11/128) on control; risk difference 2.9 percentage points (95% CI -4.4 to 10.3), risk ratio 1.34 (0.64–2.81); unadjusted two-proportion z-test p = 0.432.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Synflorix-NeisVac-C Group and the control. The interval gives the range of effects that remain compatible with the data.
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Synflorix-Menitorix Group and the control. The interval gives the range of effects that remain compatible with the data.

The registered secondary outcomes cover additional measures of meningococcal antibody, Hib antibody, pneumococcal serotype antibody, protein D antibody and hepatitis B surface antigen antibody. Some are counts above specified cut-offs, while others concern titers, concentrations or antibody activity. Together, these outcomes broaden the description beyond the primary binary rSBA-MenC result, but they address different assays and immune measures rather than repeat the same endpoint.

The detailed secondary results available in the record include rSBA-MenC threshold outcomes at age 3 and age 6. Their pattern does not simply replicate the primary age-3 comparison across every group and visit: the age-3 secondary outcome has comparisons with intervals above zero for the two listed Synflorix groups relative to the reference, whereas the age-6 comparisons include zero. This change in the pattern across visits is a reason to avoid treating one age or one antibody measure as a complete account of persistence. The secondary outcomes should be interpreted on their own definitions and time points.

The registry lists 31 secondary outcome measures, but the record does not provide a reported inferential analysis for them in the analysis summary. The outcomes also represent multiple opportunities to observe differences. General statistical explanation: when many outcomes or comparisons are examined, some results can appear notable by chance even when there is no underlying difference. Unadjusted secondary p-values therefore carry less weight than results from a clearly prespecified analysis with an appropriate multiplicity strategy. The statistical plan and any such strategy are not reported in the registry record.

Secondary findings can help assess whether the broader antibody profile is consistent with the primary outcome, but they do not automatically confirm or refute it. Differences in assay, threshold, age and endpoint scale matter. The results are best understood as a collection of exploratory or descriptive measures unless the original analysis plan indicates otherwise; that plan is not reported in the registry record.

Secondary outcomes registered for this trial, for reference (only those above were recalculated):

• Number of Subjects With an rSBA-MenC Titer Equal to or Above Cut-off Value
• rSBA-MenC Titers
• Number of Subjects With Anti-polyribosyl-ribitol Phosphate (Anti-PRP) Antibody Concentrations Equal to or Above Cut-off Values
• Anti-PRP Concentrations
• Antibody Concentrations Against Vaccine Pneumococcal Serotypes
• Number of Subjects With Opsonophagocytic Activity
• Concentration of Antibodies Against Protein D
• Number of Subjects With Anti-hepatitis B Surface Antigen (Anti-HBs) Antibody Concentrations Equal to or Above Cut-off Values

9. Statistical Interpretation

10. Statistical Methods Explained

General statistical explanation: The primary outcome is a count of participants meeting a binary criterion. For each group, the registry reports the number meeting the cut-off and the number in the group used for that outcome. A risk difference expresses the difference between the two observed proportions. A positive difference means the proportion is higher in the comparison group than in the reference group; a negative difference means it is lower. The estimate is an absolute contrast in proportions, not a ratio.

What does the interval around a risk difference tell us?

General statistical explanation: an interval estimate describes a range of values compatible with the observed data under the method used to construct it. An interval that crosses zero includes both directions of difference as well as no difference. An interval entirely on one side of zero indicates that the values in that interval are in one direction. The registry record does not state the confidence level or the interval-construction method for the posted comparisons, so those details should not be inferred from the interval values alone.

The primary comparisons list a risk difference, an interval, a p-value, a risk ratio and an odds ratio. These measures describe the same binary group data in different ways. Risk ratios compare proportions as a ratio, while odds ratios compare odds. They are not interchangeable with risk differences, and their numerical scale is different. The risk-difference results are a direct way to read the absolute contrast in the proportion above the antibody threshold. The ratios are included in the posted comparison data but do not change the endpoint’s meaning.

How should the p-values be read?

General statistical explanation: a p-value describes how incompatible the observed data are with a specified null model, assuming that model and the analysis assumptions hold. It is not the probability that the null hypothesis is true, and it does not measure the size or clinical importance of an effect. The posted p-values are explicitly unadjusted. Their interpretation therefore does not account for the multiple outcomes and comparisons in the trial record. The original statistical plan, including any planned adjustment, is not reported in the registry record.

The primary outcome description identifies an According-to-Protocol cohort for antibody persistence at 3 years of age. It includes evaluable subjects who received the full vaccination course in the primary and booster studies and had an available result at age 3. This is a selected analysis population rather than a description of every enrolled participant. General statistical explanation: restricting an analysis to participants with evaluable results can make the intended population more specific, but missing or unavailable measurements can affect how representative the analyzed group is. The registry record does not give the number excluded from the primary cohort or the reasons for missing age-3 results.

The trial is described as randomized, open-label and parallel-group. Random allocation can help balance measured and unmeasured baseline characteristics on average, but the record excerpt does not provide baseline data or the allocation method. Open-label status means masking is listed as none; the record does not clarify whether laboratory personnel were masked. The primary laboratory and the age-6 laboratory are identified, but no further assay comparability or calibration information is reported in the registry record.

Why does the antibody threshold matter?

General statistical explanation: converting a continuous measurement into a threshold outcome can simplify communication and focus attention on whether a specified criterion is met. It also loses detail. Children just below and well below a cut-off are combined, as are children just above and well above it. The binary endpoint cannot describe changes in the actual antibody titer within either category. The other registered outcomes include titers, concentrations and antibody activity measures, which address different aspects of the immune response; their presence does not make them interchangeable with the primary outcome.

The posted comparisons are labeled unadjusted recalculations in the analytical material, rather than an account of the sponsor’s prespecified model. The registry record does not report a statistical analysis plan, the original sample-size justification, covariate adjustment, interim analyses or a procedure for handling multiplicity. Because no discrepancy is identified between the posted summary values and these comparisons, there is no stated conflict requiring a different numerical result to take precedence. Still, the record’s lack of a reported analysis plan means that the comparisons should be treated as descriptive statistical contrasts, not as a complete reconstruction of the planned analysis.

General statistical explanation: binary outcomes can be analyzed with methods that compare proportions, but their results depend on the chosen estimand and method. Here, the risk difference is the absolute contrast, and the posted p-values and interval estimates are associated with the posted comparison calculations. Without a reported model or calculation procedure, details such as exact testing method, adjustment strategy and treatment of any departures from assumptions cannot be assessed. The data support describing observed group counts and the posted contrasts, while claims beyond those recorded results require caution.

11. Confidence Intervals and Precision

The posted interval estimates convey uncertainty around the age-3 risk differences. For the Synflorix-NeisVac-C comparison, the interval ranges from 0.063 to 0.183 and stays above zero. The intervals for Synflorix-Menitorix and Prevenar-Menitorix include zero, ranging from -0.052 to 0.102 and from -0.124 to 0.047, respectively. The registry record does not report the confidence level or the method used to construct these intervals, so their nominal coverage cannot be specified from this record.

General statistical explanation: a wider interval indicates less precision about the size and direction of a contrast, while a narrower interval indicates greater precision under the same method. An interval crossing zero does not prove there is no difference; it indicates that the interval includes no difference as well as values in either direction. Conversely, an interval excluding zero does not establish clinical importance. The size of the estimate, the measured endpoint, the analysis population and the limitations of the study remain relevant.

The observed group counts are not identical in size, and the primary analysis is limited to the stated evaluable cohort. The record does not report the number of missing results, missing-data handling or a sensitivity analysis. Those omissions make it difficult to judge whether the reported precision fully reflects uncertainty related to unavailable measurements. The interval estimates should therefore be read as precision around the posted group comparison, not as a complete accounting of every source of uncertainty.

For this endpoint, the central question is whether the proportion above the threshold differs across earlier vaccination groups at age 3. Precision around that contrast is distinct from precision of antibody titers themselves or from precision about clinical outcomes, neither of which is established by the primary count alone.

12. 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 trial’s original design calculation. For these binary outcomes, the figures mean participants per arm. The planning assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, a normal approximation, and an effect to detect set at the stated fraction of the observed effect. The original trial’s own design assumptions and sample-size justification are not reported in the registry record.

The 80% power column gives the illustrative number of participants per arm under which a study would have an 80% chance of detecting the specified effect, if the planning assumptions and effect were correct. The 90% power column gives the corresponding illustrative number for a 90% chance. These are prospective planning quantities. They are not a measure of the probability that the observed trial result is true and are not observed power.

The rows that use 100%, 75% or 50% of the observed effect describe progressively smaller effects to be detected. Smaller effects generally require more participants to distinguish them from random variation under otherwise unchanged assumptions. This is why the planning figures rise as the target fraction of the observed effect becomes smaller. The values are specific to the observed comparison and the stated assumptions; they should not be treated as a universal sample-size recommendation.

The displayed planning figures concern two-arm comparisons, whereas the trial has four groups and the registry record does not report its original sample-size strategy. The calculations should therefore be read as illustrations of the sample sizes associated with selected effects, not as evidence that the study was designed or powered according to those calculations. The registry record does not report the original assumptions for allocation, anticipated outcome rates or the target effect used during trial planning.

13. 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 = 0.863; treatment proportion p₁ = 0.986; average p̄ = 0.925.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.3729 = 0.7309.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.3627 = 0.3052.
4. n = (0.7309 + 0.3052)² / (0.1230)² = 71.0, rounded up to 71 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 <- 0.863309352517986                          # control proportion
p1 <- 0.986301369863014                          # 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(891176)
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 = 71 (80% power), 95 (90% power)
 75% of observed effect: n per arm = 151 (80% power), 202 (90% power)
 50% of observed effect: n per arm = 392 (80% power), 525 (90% power)
power.prop.test: 71 
Simulated power at n = 71 per arm: 0.868 (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.

14. Multiplicity, Missing Data and Analysis Populations

The registry lists a large set of antibody outcome measures and multiple comparisons among groups and ages. The primary outcome is one of these measures, while the secondary outcomes include several distinct antibody assays and forms of measurement. The posted comparison p-values are unadjusted. The record does not report whether the trial’s prespecified analysis plan used a multiplicity procedure, identified a testing hierarchy or treated the secondary outcomes as exploratory.

General statistical explanation: when many statistical tests are performed, the chance of at least one apparently unusual result can rise, even if all tested null hypotheses are true. Adjustment procedures or a prespecified hierarchy can help control the interpretation of multiple testing. Without information about the planned approach, the unadjusted comparisons should not be read as if each were the only test conducted. This concern applies especially to secondary findings and comparisons chosen after examining the data.

The primary analysis is described for an According-to-Protocol cohort at age 3, requiring completion of the full earlier vaccination course and an available result. The registry record does not state the number of participants who lacked an age-3 result, why results were unavailable, or how missing values were handled. It also does not report whether any sensitivity analyses assessed the effect of exclusions or missing measurements. Consequently, the potential influence of selection into the evaluable cohort cannot be quantified from the record.

The registry describes randomized allocation and no masking. It does not provide the randomization method, allocation concealment, baseline characteristics or details about laboratory masking. These details would help readers judge implementation and possible sources of bias. The statistical analysis plan, interim analyses, covariate adjustments and original sample-size justification are also not reported in the registry record. The posted results do not establish whether these elements were prespecified or how they were addressed in the sponsor’s analysis.

These gaps do not invalidate the recorded counts, but they limit conclusions about how fully the comparisons reflect the planned trial analysis and how confidently secondary results can be separated from chance findings.

15. 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.

The adverse-event figures list zero serious adverse events in each group: the reported at-risk counts are 144 for Synflorix-Meningitec, 147 for Synflorix-NeisVac-C, 149 for Synflorix-Menitorix and 141 for Prevenar-Menitorix. No serious adverse event terms are listed. These figures describe the safety data recorded in the extension record; they do not establish that no events occurred outside the reporting scope or in the earlier studies.

The record shows zero for both the at-risk and affected counts for other adverse events in each group. With no participants listed as at risk for that outcome, these entries do not support a meaningful comparison of other adverse events. Death counts are not reported in the registry record.

The persistence phase involved no vaccine administration, so these figures should not be interpreted as a safety comparison of newly administered vaccines in this phase. The record does not provide further detail about event definitions, collection windows or attribution. The safety information is therefore limited to the posted serious-event counts and the entries shown for other events.

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

The primary result describes the proportion of evaluable children whose age-3 rSBA-MenC titer met or exceeded the 1:8 threshold after different earlier vaccination courses. The observed count was higher in the Synflorix-NeisVac-C Group than in the Synflorix-Meningitec reference group, and the posted unadjusted interval for that risk difference stays above zero. The other two primary comparisons have intervals that include zero. These are statistical descriptions of the posted endpoint and its uncertainty.

They do not show that one vaccination course is clinically superior, establish protection against disease for any individual child, or determine how long antibody levels remain above the cut-off. The primary measure is an antibody threshold at a particular age, not a clinical disease outcome or a continuous record of each child’s antibody level. The record does not report a link between the threshold and clinical protection in this population.

The four groups reflect earlier combinations of vaccines, and the study phase under discussion administered no vaccine. The contrasts therefore cannot be interpreted as the effects of a new intervention delivered during the persistence phase. Nor do the results establish that two groups are equivalent when an interval includes zero; an absence of clear evidence of a difference is not proof of equivalence.

The age-3 primary result also cannot be generalized automatically to other ages or antibody measures. The record includes a range of secondary outcomes and describes measurement at ages 3, 4 and 6, but the statistical detail available for each outcome is not uniform. Differences in assay, time point and endpoint definition affect what each result can answer.

Finally, unadjusted comparisons, missing-data details and the original analysis plan are not reported. The most defensible reading stays close to the observed counts and posted contrasts, recognizes their uncertainty, and avoids turning antibody measurements into claims about clinical outcomes that this endpoint did not measure.

17. Why This Trial Matters Statistically

This trial illustrates a common statistical challenge in vaccine follow-up: a study may evaluate persistence through several antibody measures, ages and earlier vaccination courses, while its primary outcome captures only one threshold measure at one stated time point. The endpoint is interpretable as a count above a cut-off, but it compresses the underlying titer information and does not directly measure disease incidence.

The primary comparisons also show why effect estimates and intervals are more informative than a p-value alone. One group contrast has a posted interval entirely above zero, while the other primary intervals include zero. That difference in uncertainty is important, but it does not settle clinical importance, equivalence or the results of other antibody outcomes. The record’s unadjusted comparisons and absent multiplicity details further limit the weight that should be placed on isolated statistical findings.

The extension design creates another important interpretive distinction: the outcomes reflect persistence after earlier vaccination courses, not a vaccine administered during the persistence phase. Group labels correspond to combinations used in previous studies, so comparisons concern those earlier courses as represented in this extension cohort. The details of those preceding studies are not fully available in this record.

For biostatistical interpretation, the case underscores the value of a transparent analysis plan, explicit missing-data accounting, stated confidence levels and methods, and a clear approach to multiple outcomes. The registry provides useful counts and contrasts, but does not report these elements in enough detail to reconstruct the full inferential framework. Readers can describe what was observed while remaining cautious about broader claims.

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.

Several limitations are specific to the available record. First, the primary outcome is a threshold count at age 3, so it does not preserve the full titer distribution. Children with different titers can be classified together, and results close to the cut-off may be sensitive to measurement variation. The registry does not provide individual-level measurements or a distribution of titers for the primary endpoint.

Second, the primary analysis uses an evaluable According-to-Protocol cohort after completion of earlier vaccination courses and availability of an age-3 result. The record does not report the number excluded, the reasons for unavailable measurements or sensitivity analyses for missing data. The effect of selection into this cohort cannot be assessed from the posting.

Third, the record does not report the original statistical analysis plan, sample-size justification, interval confidence level, interval method, multiplicity procedure, interim analyses or any covariate-adjusted analyses. The posted comparisons are unadjusted, and the registry analysis summary does not list reported analyses. This limits the ability to determine how the posted calculations relate to any prespecified sponsor analysis.

Fourth, the record describes an extension after earlier vaccination studies, with different vaccination combinations across groups. The persistence phase itself administered no vaccine. The results should not be read as a direct test of a newly administered vaccine, and the earlier-course descriptions are incomplete in the available record. The age-3 and age-6 rSBA measurements were tested at different laboratories; the record does not report assay-comparability details. It also does not provide detailed statistical results for every registered outcome in the information.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Persistence of Antibodies at 3, 4 and 6 Years of Age After Vaccination With Meningococcal, Pneumococcal and Hib Vaccines — NCT00891176.
• Registry record last updated 2018-02-15; status last verified 2016-09.
• Results first posted 2010-12-23.
• 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

NCT00891176 is a completed randomized, open-label, parallel-group phase 3 extension study with 582 participants enrolled. It evaluated persistence of pneumococcal, meningococcal serogroup C, Hib and hepatitis B antibodies in children aged 3, 4 and 6 years after earlier vaccination courses. No vaccine was administered during the persistence phase.

The primary outcome was the number of subjects with an rSBA-MenC titer at or above 1:8 at age 3. The registry reports group counts and unadjusted comparisons against the Synflorix-Meningitec Group. The Synflorix-NeisVac-C contrast has an interval above zero and p < 0.001; the other two primary intervals include zero. Secondary outcomes cover multiple antibody measures, but the record does not report a multiplicity strategy, original sample-size justification or full statistical analysis plan. Missing-data details and death counts are not reported in the registry record.