A Phase III Study to Assess the Lot-to-lot Consistency of GSK's Investigational RSV Maternal Vaccine and the Immune Response and Safety of RSV Maternal Vaccine When Given Alone or Co-administered With GSK's Influenza D-QIV Vaccine in Healthy Non-pregnant Women.: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for A Phase III Study to Assess the Lot-to-lot Consistency of GSK's Investigational RSV Maternal Vaccine and the Immune Response and Safety of RSV Maternal Vaccine When Given Alone or Co-administered With GSK's Influenza D-QIV Vaccine in Healthy Non-pregnant Women. (NCT05045144), a randomized phase 3 study. The primary outcome is Percentage of Participants Reporting Solicited Administration Site Events in RSV Pooled Group, RSV+Flu Pooled Group and Flu+Placebo Group.

2. Clinical Question

The study also addressed a distinct lot-consistency objective: evaluating whether immune responses were consistent across the three RSV vaccine lots. Its additional objectives included assessing immune responses, safety and reactogenicity when RSV MAT vaccine was given with Flu D-QIV. These objectives involve different outcomes from the primary solicited administration-site endpoint. In particular, the listed secondary outcomes include RSV neutralizing antibody titers, RSV MAT IgG concentrations, and influenza antibody response measures. The registry record identifies these measurements but does not report numerical results for them in the information. The primary question is therefore about the frequency of specified local reactions, not whether the vaccine prevented RSV infection or how well it protected participants from illness.

3. Trial Design

This was a randomized, quadruple-masked, parallel-group Phase III study. The registry record reports a total enrollment of 1586 and describes the study as multi-country. It was conducted in healthy non-pregnant women 18-49 years of age. The reported study start was 2021-10-26, primary completion was 2022-06-06, and the study status is completed.

Five groups are described. Participants in the RSV lot1, RSV lot2 and RSV lot3 groups received one dose of their assigned RSV MAT vaccine lot intramuscularly at Day 1. Those groups could also receive Flu D-QIV at Day 31. The RSV+Flu pooled group received one dose of RSV vaccine from one of the three lots and one dose of Flu D-QIV on Day 1, with follow-up through Day 181. The Flu+Placebo group received Flu D-QIV with placebo on Day 1 and was also followed through Day 181. The record identifies Flu+Placebo as the comparator for immunogenicity and safety analyses of the RSV+Flu pooled group.

The primary endpoint description pools participants who received RSV vaccine alone across lots and compares the pooled RSV, RSV+Flu pooled and Flu+Placebo groups for solicited administration-site events. It says this pooling was specified because minimal differences were expected between recipients of the different RSV lots for this outcome. That rationale applies to the solicited-event endpoint; the lot-specific groups remain relevant to the lot-consistency and lot-specific immune-response objectives. The exact randomization ratio, masking procedures, and allocation concealment methods 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: As pre-specified in statistical plan, data reported in Participant Flow, Baseline Characteristics and Adverse Events were presented for individual RSV lot groups, pooled RSV+Flu group (since minimal differences were expected between participants who received different RSV lots of the vaccine) and Flu+Placebo Group. As pre-specified in protocol, immunogenicity outcome measures presented data for the pooled RSV and RSV+Flu groups, and individual RSV lot groups were used for lot-to-lot analyses.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Analysis was performed on the Solicited Safety Set (SSS), which includes all participants who received at least 1 dose of the study intervention (Exposed Set \[ES\]) and who have solicited safety data.

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 Percentage of Participants Reporting Solicited Administration Site Events in RSV Pooled Group, RSV+Flu Pooled Group and Flu+Placebo Group, measured over From Day 1 to Day 7 (including Day 7).

The primary endpoint is the percentage of participants reporting solicited administration-site events in the RSV pooled, RSV+Flu pooled and Flu+Placebo groups. The events assessed were pain, erythema and swelling. The observation period was from Day 1 to Day 7, including Day 7. The analysis population was the Solicited Safety Set, defined as participants who received at least one dose of study intervention and had solicited safety data.

This endpoint is used to describe short-term local reactogenicity after vaccination. A percentage expresses how common the specified events were among the participants counted in the analysis, while the event definitions and observation window set the scope of that summary. It is not a measure of RSV infection, disease severity, or longer-term protection. The registry description says that results were presented for pooled RSV lots, the RSV+Flu pooled group and the Flu+Placebo group because minimal differences were expected between participants receiving different RSV lots for this objective.

The registry record identifies the endpoint and its planned groups, but numerical percentages and confidence intervals for this primary outcome are not reported in the registry record. Consequently, the size and precision of the primary endpoint estimates cannot be described from the posted information. The listed adverse-event counts elsewhere in the record should not be substituted for these primary solicited administration-site results: they are distinct summaries, and the record does not identify them as the primary endpoint estimates.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The methods and concepts below explain how the recorded design and outcome summaries are generally interpreted. The registry record does not report a complete statistical analysis plan or the numerical primary-outcome results.

What does a percentage endpoint represent?

General: A percentage for an event endpoint describes the proportion of participants in a defined analysis population who experienced or reported the event during a defined observation period. Its meaning depends on the event definition, which participants are included, and the period in which events are counted. Here, the primary endpoint concerns solicited administration-site pain, erythema and swelling from Day 1 to Day 7, including Day 7. The stated analysis population is the Solicited Safety Set: participants who received at least one dose and had solicited safety data.

The registry record calls the outcome a percentage of participants and gives a 95% confidence interval as the dispersion measure. A confidence interval describes uncertainty around an estimate under the statistical method used: it is not a range containing every participant's outcome, and it does not show how individual participants' experiences varied. The numerical percentages and intervals for this primary endpoint are not reported in the registry record, so their widths and group-specific values cannot be assessed.

Why are vaccine lots pooled for this endpoint?

The primary endpoint description says that the RSV lots were pooled for the solicited-event presentation because minimal differences were expected between participants who received different lots. This is a stated rationale for presentation of this outcome, not evidence that lot-specific results were identical. Pooling combines information across the specified lots and can provide a group-level summary, but it does not answer the separate lot-to-lot consistency question. That question concerns whether responses were consistent across the three lots and is addressed by the trial's other objectives and listed outcomes.

What is the role of randomization and masking?

General: Random allocation is intended to create groups that are comparable on average with respect to measured and unmeasured characteristics, although chance imbalances can still occur. Masking is intended to reduce the influence of knowledge about assigned treatment on participant experience, care or outcome assessment. The registry classifies this trial as randomized and quadruple-masked, with a parallel-group model. It does not describe the exact randomization procedure, the allocation ratio, who was masked in practice, or how masking was maintained. Those details are not reported in the registry record.

How should group comparisons be read?

General: A comparison of event percentages considers both the observed group estimates and their uncertainty. A confidence interval around each estimate can describe the precision of that estimate, while a confidence interval for a contrast would address uncertainty in the difference between groups. Separate intervals for each group are not, by themselves, a formal test of a between-group difference. The registry record describes the groups for the primary endpoint but does not report numerical estimates or a comparative statistical test for that outcome. Accordingly, no claim about a statistically significant difference, similarity, or equivalence can be made from the primary endpoint information available.

For safety counts, denominators matter because the number of participants differs by group. Counts should be read alongside the corresponding number at risk, not as stand-alone measures. Even with denominators, descriptive event counts do not replace a prespecified comparative analysis, particularly for uncommon events. The record does not report adjusted safety comparisons or intervals for the serious adverse-event figures.

What do the antibody outcomes measure?

The listed secondary outcomes include RSV A and RSV B neutralizing antibody titers, RSV MAT IgG concentrations, and influenza hemagglutination-inhibition antibody titers, seroconversion rates and seroprotection rates. These are immunogenicity measures, not direct counts of RSV illness. Titers and concentrations summarize measured antibody responses, while seroconversion and seroprotection rates summarize the proportions meeting their respective definitions. The registry record lists the outcomes and time points but does not provide the numerical antibody results or the detailed criteria for those response definitions in the information described.

General: Immunogenicity findings can describe immune responses, but their clinical interpretation depends on validated relationships between the measure and clinical outcomes. The presence of an antibody endpoint alone does not establish prevention of infection or disease. No clinical efficacy endpoint is described among the registry entries summarized for this analysis.

What can planning illustrations tell readers?

General: A sample-size planning illustration estimates how many participants might be needed under chosen assumptions to detect a specified effect with a chosen statistical power and significance level. It is a forward-looking planning calculation, not an estimate of the chance that a completed study's result is true, and not observed power. The planning assumptions described for illustrations use a two-sided significance level of 0.05, equal allocation between two arms, a normal approximation, and an effect defined as a stated fraction of the observed effect. For time-to-event outcomes, the illustration is expressed as a total event count; for other outcomes, it is expressed as participants per arm. Numerical planning results are not reported in the registry record, and these assumptions are not evidence of the trial's original design rationale. The study's sample-size justification is not reported in the registry record.

More generally, model assumptions matter. For count outcomes, over-dispersion means that observed variability exceeds what a simpler model assumes; ignoring it can make uncertainty appear too small. This is a general statistical consideration, not a claim that over-dispersion affected the primary endpoint in this study. The endpoint is described as a percentage outcome, and the specific statistical model, any adjustment variables, and any method for handling repeated or multiple events are not reported in the registry record.

10. Multiplicity, Missing Data and Analysis Populations

The registry record lists a primary solicited administration-site endpoint and multiple secondary outcomes. These include antibody measures for RSV A and RSV B, RSV MAT IgG concentrations, and influenza antibody titers, seroconversion and seroprotection measures. When a study evaluates many outcomes, the chance of at least one apparently unusual result can increase if each result is assessed separately. General statistical approaches to this issue include defining a hierarchy of tests, adjusting significance thresholds, or treating secondary analyses as descriptive. The registry record does not report a multiplicity strategy, testing hierarchy, or adjustment method.

The record describes the Solicited Safety Set for the primary endpoint as participants who received at least one dose and had solicited safety data. It also identifies the Exposed Set as participants who received at least one dose of study intervention. The detailed membership rules for other analysis populations, and which population was used for each secondary outcome, are not reported in the registry record. The record also does not state how missing solicited safety data were handled, whether any imputation was used, or how missing antibody measurements were treated.

These omissions affect interpretation because an analysis population and missing-data approach determine which participants contribute to an estimate and what assumptions are made about unavailable measurements. If participants with missing data differ from those with observed data, a complete-case summary may not describe the full randomized group in the same way. This is a general concern, not a claim that missingness biased these results. The registry record does not report the amount or pattern of missing outcome data or sensitivity analyses evaluating its impact.

Interim analyses, stopping rules and the statistical analysis plan are not reported in the registry record. Their absence from the record means that readers cannot assess whether any planned interim review or other prespecified analysis decisions affected interpretation.

11. Safety Results

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

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: fibula fracture (0.5%), cervical dysplasia (0.5%), joint ankylosis (0.5%), suicidal ideation (0.5%), back pain (0.4%).

The registry record gives serious adverse-event counts with the number at risk for each group. Serious events were reported for 2 of 220 participants in RSV lot1, 1 of 223 in RSV lot2, 2 of 218 in RSV lot3, 4 of 438 in RSV+Flu Pooled, and 4 of 440 in Flu+Placebo. The record reports 0 deaths in each of these groups. These are participant counts and denominators, not the solicited administration-site endpoint results.

The record also reports other adverse-event counts of 182 of 220, 193 of 223, 194 of 218, 409 of 438, and 396 of 440 across those same groups. The record does not establish in the information described which specific events make up these other-event totals or whether they share the primary endpoint's observation window. They should therefore be read separately from solicited pain, erythema and swelling.

The listed serious-event terms include Fibula fracture, Cervical dysplasia and Joint ankylosis, each reported as 0.5%; Suicidal ideation, reported as 0.5%; Back pain, reported as 0.4%; and Greater trochanteric pain syndrome, reported as 0.4%. The record does not provide group assignments for these terms in the information described. Counts and listed terms do not establish causation, comparative risk or absence of risk. The registry record does not report adjusted comparisons or confidence intervals for these safety figures.

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

This trial was designed to evaluate lot-to-lot consistency of an investigational RSV maternal vaccine and to assess immune responses, safety and reactogenicity when the vaccine was given alone or with Flu D-QIV. The primary endpoint specified in the registry record measures solicited administration-site events over a short, defined period. The study design and endpoint definitions clarify what the investigators set out to assess; they are not themselves evidence that a particular result occurred.

The available registry information does not report numerical results for the primary endpoint. It therefore cannot establish how common the specified local events were in each group, how different the group estimates were, or how precise those estimates were. The listed secondary antibody outcomes likewise have no numerical results reported in the registry record. The central quantitative conclusions about reactogenicity, lot consistency and immune response cannot be reconstructed from the outcome descriptions.

The adverse-event counts provide descriptive safety information for the groups, including serious-event counts and the reported absence of deaths. These counts do not establish that events were caused by the assigned intervention, and they do not show that groups had equivalent safety profiles. Nor do they substitute for a comparative analysis of the primary solicited events.

The endpoint information does not answer whether vaccination prevented RSV infection or illness. It describes solicited local reactions and lists antibody outcomes, while the clinical efficacy findings are not reported in the registry record. General: a measured immune response is not automatically equivalent to demonstrated clinical protection; the relevance of a biomarker depends on evidence connecting it to meaningful clinical outcomes.

Thus, the record establishes the trial's population, groups, primary endpoint definition, follow-up windows, and some adverse-event counts. It leaves the main numerical outcome estimates and important analytic details unreported. Conclusions should remain limited to those documented features rather than extending to efficacy, equivalence, causality or a complete characterization of risk.

13. Why This Trial Matters Statistically

The study brings together two distinct statistical questions: whether immune responses are consistent across three vaccine lots, and how reactogenicity and immune responses look when RSV MAT vaccine is given alone or with an influenza vaccine. Keeping those questions separate matters because a pooled estimate for solicited local events does not itself demonstrate lot-to-lot consistency. Conversely, lot-specific immune-response outcomes do not replace the group summaries for local events.

The design also illustrates why endpoints and analysis populations need to be read together. The primary outcome concerns specified solicited administration-site events over a defined period, and its analysis population requires both exposure and solicited safety data. Those choices define the population and events represented by the percentage. The record's description makes those boundaries visible, even though the numerical endpoint results are not reported.

For statistical interpretation, the record is also a reminder to distinguish descriptive counts from comparative evidence. Serious adverse-event counts and denominators describe what was recorded in each group, but without comparative estimates and uncertainty they do not establish a treatment difference, equivalence or causation. Similarly, antibody outcomes can characterize immune response but are not direct evidence of clinical disease prevention.

The registry documents a randomized, quadruple-masked, parallel Phase III design, but its available outcome reporting is incomplete for evaluating the main quantitative questions. That distinction is important: the trial's intended questions and methods can be described, while conclusions about effect sizes and precision require reported estimates. A careful statistical reading makes clear both what the record permits readers to understand and what remains unresolved because key numerical results and analysis details are not reported.

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 principal limitation for interpreting this study from the registry record is that numerical results for the primary solicited administration-site endpoint are not reported. Without the group percentages and confidence intervals, the frequency and precision of the primary outcome cannot be evaluated. Numerical findings for the listed antibody outcomes are also not reported, limiting assessment of lot-to-lot consistency and immune response with co-administration.

The registry record does not report the sample-size justification, statistical analysis plan, multiplicity approach, interim analyses, or stopping rules. It also does not provide the detailed randomization procedure, allocation ratio, masking procedures, or methods for handling missing outcome data. These details are relevant to evaluating how analyses were planned and conducted, but they cannot be inferred from the randomized and quadruple-masked classifications alone.

The primary analysis population excludes participants without solicited safety data, according to the stated definition. The record does not report how many participants were excluded from that population, the extent of missing data, or whether sensitivity analyses were conducted. The available information also does not establish the detailed definitions or observation windows for the other adverse-event counts. As a result, those counts cannot be treated as interchangeable with the primary solicited local-event outcome.

The population was healthy non-pregnant women 18-49 years of age. Generalizability to other populations or settings cannot be assessed from this study description alone. Finally, the registry record describes immune and safety outcomes but does not report clinical efficacy results. These limitations do not show that the study was conducted improperly; they identify the boundaries of what can be interpreted from its reported record.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: A Phase III Study to Assess the Lot-to-lot Consistency of GSK's Investigational RSV Maternal Vaccine and the Immune Response and Safety of RSV Maternal Vaccine When Given Alone or Co-administered With GSK's Influenza D-QIV Vaccine in Healthy Non-pregnant Women. — NCT05045144.
• Registry record last updated 2023-10-05; status last verified 2023-09.
• Results first posted 2023-10-05.
• 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

This completed randomized, quadruple-masked, parallel Phase III study enrolled 1586 healthy non-pregnant women 18-49 years of age. It evaluated three lots of RSV MAT vaccine, RSV vaccine co-administered with Flu D-QIV, and a Flu+Placebo comparator group. The primary endpoint was the percentage reporting solicited administration-site pain, erythema or swelling from Day 1 to Day 7, including Day 7, in the Solicited Safety Set.

The registry record reports serious adverse-event counts, other adverse-event counts and 0 deaths in each group. Numerical results for the primary endpoint and listed antibody outcomes are not reported in the registry record. The sample-size justification, detailed statistical analysis plan, multiplicity strategy and missing-data methods are also not reported in the registry record. The posted information therefore describes the trial design and selected safety counts but does not permit evaluation of the primary outcome's magnitude or precision.