A Study to Assess the Safety, Tolerability, and Immunogenicity of RSVpreF in Older Adults in Korea: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for A Study to Assess the Safety, Tolerability, and Immunogenicity of RSVpreF in Older Adults in Korea (NCT06593587), a randomized phase 3 study. The primary outcome is Percentage of Participants With Local Reactions Within 7 Days After Vaccination.

2. Clinical Question

The trial also addresses immune response. Its stated goal is to quantify the immune response after vaccination and examine antibody-level changes before and after vaccination. A listed secondary outcome is seroresponse rates of neutralizing titers for RSV A and RSV B at 1 Month After Vaccination. The registry record does not report results for that outcome.

Safety questions include local reactions, systemic events, and medical problems after vaccination. The primary endpoint focuses specifically on local reactions: redness, swelling, or injection-site pain at least mild in severity. Participants were asked to record symptoms in a diary for 7 days after vaccination. The description also notes a clinic visit a month later and health-check phone calls 1 week and 2 months after vaccination.

The study is described as randomized, quadruple-masked, and parallel. Those design labels identify the broad comparison structure, but the registry record does not provide further details about the randomization procedure or which roles were masked. Registered enrollment is 378. The results available in the registry record do not include a primary endpoint comparison, so the clinical question cannot be answered from the posted results alone.

3. Trial Design

This is a Phase 3 randomized, quadruple-masked, parallel study of RSVpreF and placebo in older adults in Korea. The registry record lists Pfizer as the sponsor and gives the condition as Respiratory Syncytial Virus. The registered enrollment is 378. The intervention description says participants receive RSVpreF or placebo once at Visit 1. The adverse-event groups are titled RSVpreF 120 mcg and Placebo.

The study description outlines follow-up focused on symptoms, safety, and immune response. Participants were asked to keep a symptom diary for 7 days after vaccination. The description also specifies a phone call 1 week after vaccination, a clinic visit a month later for a checkup and tests, and another health-check phone call 2 months after vaccination. The primary endpoint uses the interval from Day 1 to Day 7 after vaccination. The listed secondary outcome concerns neutralizing titers for RSV A and RSV B at 1 Month After Vaccination.

The registry record gives a start date of 2024-10-07, a primary completion date of 2025-02-03, and a status of COMPLETED. These dates describe the registered study timeline; they do not substitute for outcome results. Although the study is marked randomized and quadruple-masked, the registry record does not report the randomization method, allocation concealment details, or the identities of the masked groups of people.

The primary safety population is described as all screened participants who received study intervention in the study. The adverse-event results give risk denominators separately for RSVpreF and placebo. The record does not explain how those outcome-specific denominators relate to the registered enrollment. It lists nine outcome measures and zero analysis entries. It does not report the primary endpoint values by group, an effect estimate comparing groups, or a statistical analysis plan. Accordingly, the design can be described, but a comparative estimate of the primary outcome cannot be interpreted from 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: A total of 384 participants were screened, out of which 6 were screen failures and 378 participants were randomized 2:1 to receive respiratory syncytial virus stabilized prefusion F subunit vaccine (RSVpreF) or placebo.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Safety population included all screened participants who received the study intervention in the study.

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 screened participants who received the study intervention in the study.

6. Primary Endpoint

The registry lists the primary outcome as Percentage of Participants With Local Reactions Within 7 Days After Vaccination, measured over From Day 1 to Day 7 after vaccination.

The primary endpoint is the percentage of participants with a local reaction from Day 1 to Day 7 after vaccination. A local reaction is any redness, swelling, or injection-site pain at least mild in severity. This combines three types of injection-site response into a participant-level indicator: a participant meets the endpoint if at least one qualifying reaction occurs during the stated period.

Redness and swelling were measured using measuring-device units, with 1 measuring device unit equal to 0.5 centimeter. The record classifies redness and swelling as mild when greater than 2.0 cm to 5.0 cm, moderate when greater than 5.0 cm to 10.0 cm, and severe when greater than 10.0 cm. Pain is graded by its effect on activity: mild does not interfere with activity, moderate interferes with activity, and severe prevents daily activity. These definitions establish how the endpoint's component events are categorized.

As a general statistical rationale, a participant-level percentage is useful for summarizing how commonly an event occurs in a defined group over a specified follow-up period. It makes the outcome interpretable as the share of participants experiencing at least one qualifying local reaction, rather than the total number of individual symptoms. The record specifies an exact two-sided 95% confidence interval using the Clopper and Pearson method. However, the percentage and interval for either group are not reported in the registry record, so the endpoint's observed frequency and precision cannot be assessed from the posted results.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry record describes a percentage endpoint and an exact two-sided 95% confidence interval using the Clopper and Pearson method. It does not report the observed primary endpoint percentages or intervals. The method can therefore be explained, but no numerical endpoint estimate can be interpreted from the registry record.

What does a percentage endpoint represent?

As a general statistical explanation, a percentage for a binary outcome summarizes how many participants in a defined group experienced the event, relative to the participants assessed for that outcome. In this trial, the event is a local reaction meeting the stated definition during the specified post-vaccination period. A participant is counted as having the endpoint if redness, swelling, or injection-site pain meets the threshold for at least mild severity. This participant-level approach avoids counting repeated symptoms as if each were a separate participant. It does not, by itself, convey how many episodes occurred, how long reactions lasted, or how severe the typical reaction was.

The denominator matters because a percentage is interpreted in relation to the participants included in that endpoint analysis. The registry record defines the primary safety population as all screened participants who received study intervention. It does not report primary endpoint denominators by group or explain how missing diary entries or incomplete follow-up would be handled. The adverse-event denominators are reported separately, but they should not be assumed to be the primary endpoint denominators.

Why report a confidence interval?

In general, a confidence interval communicates the statistical uncertainty around an estimate. A narrower interval indicates greater precision under the assumptions of the method; a wider interval indicates less precision. It is not a measure of the clinical importance of an outcome, and it cannot correct for bias caused by missing data, measurement problems, or differences in who is analyzed. The registry record specifies a two-sided 95% interval but does not report the interval endpoints for the primary outcome.

The Clopper and Pearson approach is an exact method for constructing an interval for a binomial proportion. In general, exact methods are based on the discrete distribution of event counts rather than relying only on a large-sample approximation. Such intervals can be conservative, meaning their actual coverage may exceed the nominal level in some settings. This method choice does not eliminate the need to know the event count and denominator, and it does not provide an interval in the absence of the observed outcome data.

What does the study design contribute?

Randomization is intended, in general, to make assigned groups comparable in expectation with respect to factors that could affect outcomes. Masking is intended to reduce the potential influence of expectations on care, reporting, or assessment. The registry labels this study randomized and quadruple-masked, but does not report the randomization procedure or identify which people were masked. The record describes a parallel design, meaning the comparison is between groups followed within the study rather than a crossover description. These labels alone do not establish that the groups were comparable in the realized sample or that all possible sources of bias were controlled.

The posted information gives a safety population definition and adverse-event denominators, but it does not report an analysis population for the primary endpoint. The population definition is important because results can differ depending on who is included and how participants with missing observations are handled. The registry record does not report whether any observations were missing, how missingness was assessed, or whether an alternative analysis was conducted.

How should the adverse-event counts be read?

As a general statistical explanation, counts describe the observed number of participants affected, while risk denominators identify the group size used for that particular adverse-event reporting. The serious adverse-event counts are 2 in the RSVpreF group and 1 in the placebo group; the corresponding risk denominators are 251 and 126. The record also gives the counts for other adverse events and deaths. These values are descriptive; without a reported analysis, they do not establish a treatment effect or quantify uncertainty around a between-group difference.

Over-dispersion is a general concern when event data vary more than a simple statistical model expects. For example, participants can differ in underlying susceptibility, and events can cluster by time or circumstance. When that occurs, a model that assumes less variability may understate uncertainty. The registry record does not report a model for event counts or an over-dispersion assessment, so no claim about such modeling can be made for this study.

What can be said about planning illustrations?

The registry record describes planning illustrations based on fractions of an observed effect, with a two-sided significance level of 0.05, equal allocation between arms, and a normal approximation. It specifies that non-time-to-event illustrations are expressed as participants per arm for a stated power, while time-to-event illustrations use total events. These are general planning assumptions and are not observed trial results or observed power. The registry record does not report a sample-size justification for the trial's own design. No numerical planning estimates are reported in the available information, and they should not be confused with the registered enrollment or the adverse-event denominators.

10. Multiplicity, Missing Data and Analysis Populations

The registry record lists nine outcome measures and zero analysis entries. It identifies a primary local-reaction outcome and a secondary outcome concerning neutralizing titers for RSV A and RSV B at 1 Month After Vaccination, but does not report results for either in the information available. A multiplicity strategy is not reported in the registry record. That means the record does not explain whether or how statistical testing across multiple outcomes or time points would be controlled. Without that information or outcome analyses, no conclusion about multiplicity-adjusted inference can be drawn.

Missing-data methods are also not reported in the registry record. The primary endpoint depends on symptoms recorded during the 7-day period, and the study description says participants were asked to keep a diary. The record does not say whether diaries were incomplete, how incomplete records were treated, or whether missingness was considered in the analysis. It also does not report a sensitivity analysis for missing observations. These details matter because the observed percentage can depend on which participants have usable outcome data and how absent information is handled.

The primary safety population is defined as all screened participants who received study intervention in the study. The registry record does not state whether this definition applies to every outcome analysis or give primary endpoint denominators for each group. It lists adverse-event denominators of 251 for RSVpreF and 126 for placebo, but those figures are reported for adverse-event summaries and should not be assumed to describe the primary endpoint analysis population.

The record describes the trial as randomized, but does not report a detailed statistical analysis plan, analysis sets for the immune outcome, or methods for handling deviations from assigned intervention. The absence of these details limits assessment of how outcomes were selected, how missing observations might affect estimates, and whether any planned analytic safeguards were used. These are reporting limitations; they do not establish that a particular method was or was not used outside what the registry record states.

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: retinal detachment (0.8%), enteritis (0.4%), asthma (0.4%).

The registry record reports serious adverse events by group as counts of participants affected and participants at risk. For RSVpreF 120 mcg, 2 participants were affected and 251 were at risk. For placebo, 1 participant was affected and 126 were at risk. Deaths are listed as 0 in each group. Other adverse events affected 100 participants in the RSVpreF group and 43 in the placebo group; the reported risk denominators are 251 and 126, respectively.

These counts are descriptive and should be read with their denominators. They do not show how events were distributed over time, how many individual events each affected participant experienced, or whether events were judged related to study intervention. The registry record does not report a statistical comparison or confidence intervals for these adverse-event summaries. It also does not explain whether all event categories use the same ascertainment rules.

The record lists Retinal detachment at 0.8%, Enteritis at 0.4%, and Asthma at 0.4% as the top serious terms. The group attribution for those term percentages is not reported in the registry record. These summaries should not be taken as complete descriptions of each event or as evidence of causation. The counts and listed terms provide a limited descriptive account, not a standalone estimate of comparative safety.

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

The record establishes what the trial was designed to study: local reactions after vaccination, broader safety and tolerability, and immune response after RSVpreF compared with placebo. It also defines how local redness, swelling, and pain were graded and identifies a specific follow-up window for the primary endpoint. Those details make the intended outcome clearer, but they are not results.

The primary endpoint values are not reported in the registry record. There is no reported percentage for participants with a local reaction in either group, no corresponding confidence interval, and no reported comparison between RSVpreF and placebo. The listed secondary neutralizing-titer outcome also has no reported result. Thus, the posted results do not establish the observed frequency of local reactions or the measured immune response.

The serious and other adverse-event counts provide descriptive safety information, as do the reported death counts and serious-event terms. They do not, on their own, establish that one group had more or fewer events in a way that is distinguishable from random variation. The registry record does not provide a comparative estimate, uncertainty interval, or event-relatedness information for these summaries. The listed term percentages also lack group attribution in the reported information.

In general, an observed difference between groups is not the same as a causal or clinically meaningful difference. Interpretation depends on the outcome definition, analysis population, missing-data handling, uncertainty, and the analysis plan. Several of those details are not reported in the registry record, and the principal outcome estimates are absent. The study's randomized and masked labels describe intended design features, not a substitute for the results or for assessment of how the study was conducted.

The record lists enrollment of 378 and is marked COMPLETED, with a primary completion date of 2025-02-03. Completion status does not imply that results are posted or that every planned analysis is available. The sound conclusion is limited: the registry record describes a completed randomized comparison and reports selected adverse-event counts, while leaving the primary endpoint and immune-response results unreported.

13. Why This Trial Matters Statistically

This trial illustrates why outcome definitions and results availability must be considered separately. The primary endpoint is described in operational terms: it concerns any qualifying local reaction, including redness, swelling, or injection-site pain, during the specified period after vaccination. The record also defines severity thresholds for the different reaction types. These details support consistent interpretation of what the endpoint is intended to count.

Yet a precise definition does not reveal an observed frequency. Without group-specific endpoint percentages and confidence intervals, readers cannot assess the size or precision of the primary safety outcome. The listed interval method is informative about the intended statistical summary, but the interval itself is not reported. This distinction is central to biostatistical reading: methods specify how evidence could be summarized, while results show what the study observed.

The registry also demonstrates the importance of matching denominators to outcomes. Adverse-event denominators are available, but the primary endpoint denominators are not stated. Those quantities should not be treated as interchangeable. A percentage's interpretation depends on its analyzed population and on how missing measurements are handled, details that are not reported for the primary endpoint.

Finally, descriptive adverse-event counts and a completed-study status do not replace a comparative analysis. The record lists a randomized, quadruple-masked design, but provides no reported primary outcome contrast or statistical plan. The trial therefore offers a useful example of the difference between a registered study design, event summaries, and the evidence needed to evaluate a prespecified comparison. It also shows why transparent reporting of analysis populations, uncertainty, missing-data methods, and multiplicity plans matters when interpreting clinical research.

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 trial from the registry record is that the primary endpoint result is not reported. The record provides the endpoint definition and confidence-interval method, but no group-specific percentage, interval, or comparative estimate. The listed secondary immune-response outcome also has no reported results. This prevents evaluation of the central safety and immunogenicity questions using the posted results.

Details needed to assess the analysis are limited. A statistical analysis plan is not reported in the registry record, nor are multiplicity procedures, missing-data methods, or sensitivity analyses. The primary safety population is defined, but primary endpoint denominators by group are not reported. The adverse-event denominators cannot be assumed to be the denominators for the primary endpoint. The record also does not give details of the randomization procedure or identify which roles were masked.

The adverse-event summaries do not provide a full account of event timing, duration, severity distribution, relatedness, or clinical course. Although serious adverse-event counts, other adverse-event counts, deaths, and selected serious terms are listed, the term percentages are not attributed to a group in the reported information. No comparative statistical analysis or uncertainty intervals for these summaries are reported.

The registry record states that the trial is completed and gives registered enrollment and completion information, but completion status does not fill in missing outcome results. The information available does not explain the relationship between registered enrollment and the outcome-specific denominators. It also does not report whether all planned outcomes were analyzed or whether any data were unavailable. These limitations restrict interpretation to the design description and the adverse-event summaries that are explicitly reported.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: A Study to Assess the Safety, Tolerability, and Immunogenicity of RSVpreF in Older Adults in Korea — NCT06593587.
• Registry record last updated 2026-02-09; status last verified 2026-01.
• Results first posted 2026-02-09.
• 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 record describes NCT06593587, a completed Phase 3 randomized, quadruple-masked, parallel study of RSVpreF versus placebo in older adults in Korea. Pfizer is listed as sponsor, and registered enrollment is 378. The intervention description specifies a single vaccination or placebo injection. The primary outcome is the percentage of participants with local reactions from Day 1 to Day 7 after vaccination, with a two-sided 95% confidence interval specified by the Clopper and Pearson method.

The record lists a secondary outcome for neutralizing titers for RSV A and RSV B at 1 Month After Vaccination, but does not report its result. It also reports serious and other adverse-event counts, deaths, and selected serious-event terms. The primary endpoint percentages, confidence intervals, and between-group comparison are not reported in the registry record. Missing-data procedures, multiplicity methods, and a detailed statistical analysis plan are also not reported.