A Phase 1/2, Randomized, Placebo-controlled, Observer-blinded Trial To Evaluate The Safety, Tolerability, And Immunogenicity Of A Multivalent Group B Streptococcus Vaccine In Healthy Adults 18 To 49 Years Of Age: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for A Phase 1/2, Randomized, Placebo-controlled, Observer-blinded Trial To Evaluate The Safety, Tolerability, And Immunogenicity Of A Multivalent Group B Streptococcus Vaccine In Healthy Adults 18 To 49 Years Of Age (NCT03170609), a randomized phase 2 study. The primary outcome is Percentage of Participants With Clinical Laboratory Abnormalities at 1-Week After Vaccination as Measured by Food and Drug Administration (FDA) Grade.

2. Clinical Question

3. Trial Design

The registry describes a randomized, placebo-controlled, observer-blinded Phase 1/2 study. Its title identifies it as Phase 1/2, while the registry phase classification is Phase 2. The model is recorded as sequential, but the registry record does not report the sequence or explain how the study stages were organized. The study is described as first-in-human and was sponsored by Pfizer.

Participants were healthy adults aged 18 to 49 years with no history of group B streptococcal vaccination. The study compared a single intramuscular dose of multivalent group B streptococcus vaccine with saline placebo. Vaccine groups varied by dose level and by whether aluminum phosphate was included. The registry lists three dose levels in each of those formulation categories, alongside the placebo group.

Enrollment was 365. For the adverse-event summaries, each of the seven groups lists 52 participants at risk. These group-specific figures describe the safety information recorded for those outcomes; they should not be treated as the denominator for every endpoint. The registry record does not report further details about allocation procedures, concealment, or how participants were assigned among groups.

The primary outcome was the percentage of participants with clinical laboratory abnormalities at one week after vaccination, graded using FDA criteria. A secondary outcome concerned GBS6 serotype-specific IgG geometric mean concentrations one month after vaccination. The registry record does not report numerical results for either outcome in the information available for this analysis.

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.

Only the first 6 of 7 groups are shown.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Analysis population for this outcome measure included a subset of participants who received GBS6 vaccine or placebo.

5. Baseline Characteristics

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

Population: Safety population included all participants who received either GBS6 vaccine or placebo.

Only the first 6 of 8 groups are shown.

6. Primary Endpoint

The registry lists the primary outcome as Percentage of Participants With Clinical Laboratory Abnormalities at 1-Week After Vaccination as Measured by Food and Drug Administration (FDA) Grade, measured over 1 week after vaccination.

The primary endpoint measures the percentage of participants with clinical laboratory abnormalities at one week after vaccination, classified by FDA grade. It includes abnormalities in blood counts and chemistry measures, such as hemoglobin, leukocytes, neutrophils, platelets, liver-related tests, bilirubin, blood urea nitrogen, and creatinine. The registry describes grade thresholds for these measures. It also states that categories with at least one participant with an abnormality are reported.

This endpoint is used to describe laboratory safety findings after vaccination. Grading distinguishes the recorded degree of abnormality rather than treating every result outside a reference range as equivalent. The endpoint is not a measure of whether participants developed group B streptococcal infection, and it does not directly measure vaccine-induced immunity. The listed secondary outcome addresses immunogenicity through GBS6 serotype-specific IgG geometric mean concentrations at one month.

The endpoint title specifies a percentage, but the registry record does not report the percentages or grade-specific counts. It also identifies the analysis population only as a subset of participants who received vaccine or placebo; the subset size and the denominator for each laboratory measure are not reported in the registry record. Consequently, the endpoint definition can be described, but its observed distribution cannot be interpreted from the available results.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry describes a randomized comparison, but the information available does not include a reported statistical analysis for the primary outcome. The registry lists 0 analyses. No inferential estimate, confidence interval, or p-value for the laboratory-abnormality endpoint is reported in the registry record. The distinctions below explain how such statistics are generally used; they are not results from this trial.

What does a percentage endpoint represent?

General statistical explanation. A percentage endpoint for participants with an event is a binary outcome: each participant is classified as having or not having the specified event under the endpoint definition. The percentage describes the observed frequency in the analysis population. Its interpretation depends on knowing the denominator, the event definition, and how participants with missing measurements were handled. Here, the primary endpoint is defined as laboratory abnormalities by FDA grade at one week. The registry record does not report the observed percentages or the denominator for each category.

Because the endpoint includes multiple laboratory measures and grades, a participant could potentially contribute findings to more than one category. A percentage for one category should not be assumed to represent the percentage with any abnormality across all tests unless the endpoint definition says so. The registry record says categories with at least one participant with an abnormality are reported, but it does not provide the category-level outcome values in the information available for this analysis.

What would a confidence interval add?

General statistical explanation. A confidence interval describes the statistical uncertainty around an estimated quantity. For a percentage, it would indicate a range of values compatible with the observed data under the interval method’s assumptions. A narrower interval generally indicates greater precision, while a wider interval indicates less precision. An interval does not remove uncertainty, and it does not by itself establish that a difference between groups is important.

No confidence interval for the primary outcome is reported in the registry record. The safety summaries give participant counts at risk and counts affected for serious events, but do not report confidence intervals around those counts or a between-group contrast. The recorded counts can therefore be read descriptively, not as evidence of a statistically established difference.

How should a group comparison be interpreted?

General statistical explanation. A comparative analysis of binary outcomes might estimate a difference in percentages, a ratio of percentages, or another contrast. Each expresses a different aspect of the comparison. Such estimates require clearly defined groups and outcome denominators, and their uncertainty should be reported alongside them. A p-value, when used, summarizes how compatible the data are with a specified null hypothesis under the analysis assumptions; it does not measure the size or clinical importance of an effect.

The registry record does not report a comparative analysis for the primary laboratory endpoint, and it does not report p-values or confidence intervals for the adverse-event group counts. No group comparison should be reconstructed from the descriptive information alone. The record also does not report whether any model adjustment or stratification was planned or used.

What do the planning assumptions mean?

General statistical explanation. Sample-size planning illustrations estimate how many participants might be needed to detect a specified effect under stated assumptions. They are prospective planning calculations, not measures of the probability that an already completed trial found an effect. The registry’s planning assumptions describe a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. The assumed effect is expressed as a stated fraction of the observed effect. Time-to-event illustrations use total events, while other illustrations use participants per arm.

Those assumptions do not describe the trial’s own design justification. The record does not report the trial’s sample-size justification, and the assumptions alone do not establish that the trial was adequately powered for the primary endpoint. No calculated planning sample sizes for a specific comparison are reported in the available information. Since no primary outcome estimate is reported, the precision of that endpoint and any planning illustration based on its observed effect cannot be assessed from these results.

The study is identified as sequential, but the registry record does not report interim analyses or stopping rules. The record also does not report the statistical methods used to analyze the laboratory endpoint. Those omissions matter because analysis choices can affect how estimates and uncertainty are interpreted. They should not be filled in by assuming a standard approach.

10. Multiplicity, Missing Data and Analysis Populations

The primary outcome covers multiple laboratory measures and FDA grades, and the registry lists a secondary immunogenicity outcome. Seven outcome measures are recorded overall. When a study evaluates several outcomes, grades, or time points, multiple statistical tests can increase the chance of finding an apparently notable result by chance. General statistical explanation. A prespecified testing hierarchy or adjustment can address some multiplicity concerns, but the appropriate approach depends on the study’s analysis plan and the claims being evaluated.

The registry record does not report a multiplicity strategy, a hierarchy among outcomes, or an analysis plan for the laboratory categories. It also lists 0 analyses, so no reported inferential results are available to assess for multiplicity. The registry record does not report whether all planned analyses were completed or whether the posted outcome information is complete.

The primary outcome population is described as a subset of participants who received vaccine or placebo. The size of that subset, the criteria for inclusion, and the analysis denominators are not reported in the registry record. Missing laboratory measurements, reasons for missingness, and the handling of missing data are also not reported. These details are important because the percentage for an endpoint depends on which participants contribute data and how incomplete observations are treated.

Although the study is randomized, the registry record does not report whether analyses followed an intention-to-treat, per-protocol, or other analysis-population definition. The available record therefore supports only a limited description of the intended population and outcome definitions, not a full evaluation of analysis-population selection or missing-data bias.

11. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 5% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: diabetic ketoacidosis (1.9%), completed suicide (1.9%), metrorrhagia (1.9%).

The serious adverse-event summaries list 52 participants at risk in each of the six vaccine groups and the placebo group. The numbers affected were 1 in each of the 5 microgram with aluminum phosphate, 10 microgram with aluminum phosphate, and 20 microgram with aluminum phosphate groups; the other three vaccine groups and placebo each had 0 affected. These are counts within each group, not comparative estimates.

The registry lists one death in the 10 microgram with aluminum phosphate group and zero in the other groups. It also lists diabetic ketoacidosis, completed suicide, and metrorrhagia as serious adverse-event terms, each with a frequency of 1.9%. The registry record does not identify which group each listed term occurred in, nor does it report a causal assessment for the events.

The summaries also give counts for participants with other adverse events: 40, 35, 39, 36, 41, 36, and 35 across the six vaccine groups and placebo, respectively. These event counts should be read separately from the serious-event counts. The registry record does not provide comparative statistical analyses or uncertainty estimates for these summaries.

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

The registry record establishes the study’s basic comparison: healthy adults aged 18 to 49 years were randomized to receive a single dose of one of several multivalent group B streptococcus vaccine formulations or saline placebo. The primary endpoint was a laboratory safety measure one week after vaccination. A secondary outcome concerned GBS6 serotype-specific IgG geometric mean concentrations one month after vaccination.

The available information does not report numerical results for either of those outcomes. It therefore cannot show the observed frequency or grade of laboratory abnormalities, the magnitude of any antibody response, or how those outcomes compared between vaccine groups and placebo. No confidence intervals, p-values, or comparative analysis for the primary outcome are reported in the registry record.

The adverse-event data provide a descriptive account of participants affected in each group. They include serious adverse-event counts, a death count, and counts for other adverse events. These records are useful for understanding what was reported, but the counts alone do not quantify uncertainty or establish a difference between groups. The serious-event terms are listed without group attribution in the information available, and the registry does not report a causal assessment for them.

In general, a randomized design helps make groups comparable on average, but randomization does not guarantee identical groups or remove uncertainty. General statistical explanation. A sound interpretation also depends on outcome definitions, the analysis population, missing-data handling, and uncertainty estimates. Several of those details are not reported in the registry record. The study’s enrollment and design should not be mistaken for evidence of an outcome that is not numerically reported. The record supports a description of the trial and selected safety counts, but not a conclusion about the primary endpoint or comparative effects.

13. Why This Trial Matters Statistically

This trial is statistically notable for combining several formulation groups with a placebo group in an early-phase, randomized study. The vaccine groups differed by dose level and by presence or absence of aluminum phosphate. Such a structure can support descriptive comparisons across formulations, but interpreting those comparisons depends on outcome-specific denominators, uncertainty estimates, and a clearly reported analysis plan.

The primary endpoint is not a single clinical event. It covers abnormalities across several laboratory measures, each classified by grade. That kind of endpoint requires careful reporting: readers need to know which categories occurred, how many participants contributed data, and whether participants could be counted in more than one category. The registry record describes the grading approach and states that categories with at least one participant with an abnormality are reported, but the available information does not include the resulting percentages or counts.

The record also illustrates why descriptive event counts and inferential comparisons should be kept distinct. Counts of serious and other adverse events communicate what was recorded in each group; without uncertainty estimates or a reported comparative analysis, they do not establish how groups differ statistically. Likewise, planning assumptions are not trial results or evidence of observed power.

Finally, the separation between safety and immunogenicity outcomes matters. Laboratory abnormalities are the primary outcome, while the recorded secondary outcome concerns antibody concentrations. Neither outcome’s numerical results are reported in the available information. Statistical interpretation is therefore constrained less by the trial’s stated design than by the limited results and analysis details recorded.

14. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

The main limitation for interpreting the primary endpoint is that its observed percentages and grade-specific counts are not reported in the registry record. The endpoint population is described only as a subset of participants who received vaccine or placebo. Its size, selection criteria, and measurement-specific denominators are not reported, so the precision and completeness of the outcome cannot be assessed.

The record lists 0 analyses and does not report confidence intervals, p-values, or comparative estimates for the primary outcome or adverse-event summaries. It also does not report the statistical analysis plan, multiplicity approach, missing-data handling, or the trial’s sample-size justification. Interim analyses and stopping rules are not reported. Although the study is classified as sequential, the registry does not explain what that meant for study conduct or analysis.

The serious adverse-event terms are listed with percentages but without group attribution in the information available. The death count is reported by group, but the registry does not provide a causal assessment. The other adverse-event counts are also descriptive and are not accompanied by comparative uncertainty estimates.

These gaps limit interpretation of both the outcomes and the analysis process. The registered design and event counts can be described, but they do not fill in unreported primary endpoint results, establish group differences, or resolve questions about missing observations and analysis populations.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: A Phase 1/2, Randomized, Placebo-controlled, Observer-blinded Trial To Evaluate The Safety, Tolerability, And Immunogenicity Of A Multivalent Group B Streptococcus Vaccine In Healthy Adults 18 To 49 Years Of Age — NCT03170609.
• Registry record last updated 2019-07-02; status last verified 2019-06.
• Results first posted 2019-07-02.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

18. Record Summary

The registry describes a completed, randomized, placebo-controlled, observer-blinded Phase 1/2 study of a multivalent group B streptococcus vaccine in healthy adults aged 18 to 49 years with no history of group B streptococcal vaccination. The study enrolled 365 participants and compared six vaccine formulations with saline placebo. The vaccine groups varied by dose level and inclusion of aluminum phosphate.

The primary outcome was the percentage of participants with FDA-graded clinical laboratory abnormalities one week after vaccination. A secondary outcome concerned GBS6 serotype-specific IgG geometric mean concentrations one month after vaccination. Numerical results for these outcomes and statistical analyses are not reported in the registry record. The registry does report group-level counts for serious and other adverse events, and one death in the 10 microgram with aluminum phosphate group.