This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for The ARCT-154 Self-Amplifying RNA Vaccine Efficacy Study (ARCT-154-01) (NCT05012943), a randomized phase 2, phase 3 study. The primary outcome is Number of Participants Reporting Solicited Local Adverse Reactions (ARs).
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT05012943 |
| Phase | Phase 2, Phase 3 |
| Condition | COVID-19 Vaccines |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | Triple |
| Enrollment | 19474 |
| Arms in the primary outcome | n/a |
| Lead sponsor | Vinbiocare Biotechnology Joint Stock Company |
| Results posted | Yes |
2. Clinical Question
Population
Adults enrolled in Vietnam across the study parts. Phase 1 was for healthy individuals 18 to < 60 years of age; Phase 2, Phase 3a and Phase 3b included adults with and without underlying medical conditions.
Intervention
ARCT-154, a self-amplifying RNA SARS-CoV-2 vaccine. The described first series consisted of two doses of 5 µg, with a 28 day interval.
Comparator
Placebo (normal saline) in the relevant study parts, and Astra Zeneca COVID-19 vaccine in Phase 3c. The registry describes randomized assignment and an observer-blind, controlled study.
Primary question
How many participants reported solicited local adverse reactions within 7 days after Dose 1 and Dose 2, through the stated Day 7 and Day 36 time points?
The registry describes a broader evaluation of safety, immunogenicity and efficacy. The stated primary endpoint, however, concerns solicited local reactions: injection site erythema, pain, induration or swelling, and tenderness. It is not itself a measure of vaccine efficacy or immune response.
Other listed outcomes include neutralizing-antibody and spike-protein IgG measures, seroconversion, and first occurrence of severe COVID-19. The registry record does not report a single primary-outcome comparison estimate in the information covered by this analysis. The clinical question can therefore be defined from the endpoint description, but its comparative numerical answer cannot be read from the reported figures.
3. Trial Design
The registry identifies NCT05012943 as a randomized, parallel study with triple masking. Its official title describes an observer-blind controlled study, and the brief summary describes placebo control. The record lists Phase 2 and Phase 3, while the study summary describes a Phase 1/2/3 programme made up of several parts, including Phase 3c. These descriptions indicate that the study included different populations and comparisons rather than one identical comparison across every part.
The study summary describes four earlier parts: Phase 1 for safety in healthy individuals, Phase 2 for safety and immunogenicity, Phase 3a for safety, immunogenicity and efficacy, and Phase 3b for safety and efficacy. Phase 3c is described as a comparison of ARCT-154 with Astra Zeneca COVID-19 vaccine, including assessment of immunogenicity non-inferiority. Placebo is also listed as an intervention, alongside both vaccines.
The planned first vaccination series for ARCT-154 and placebo consisted of two vaccinations at a 28 day interval. The ARCT-154 dose is described as 5 µg. The registry states that participants in the earlier parts could be assigned to a study group receiving up to two vaccination series; further detail on those series is not reported in the registry record.
The reported total enrollment is 19474. The study status is completed. The recorded start date is 2021-08-15, and the primary completion date is 2023-01-18. These design and enrollment details describe the study structure, not the size of the analysis population for any particular endpoint. For the primary endpoint, the record specifies a reactogenicity analysis set that required a received dose and at least one diary report.
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, data were collected and are reported per vaccine group overall for all study phases combined. Data are reported per first treatment received.
Overall Study
| Stage | Placebo | ARCT-154 | Astra Zeneca COVID-19 vaccine |
|---|---|---|---|
| STARTED | 8300 | 9992 | 1182 |
| Phase 1: Received ARCT-154 D1-92 | 0 | 74 | 0 |
| Phase 1: Received Placebo D1-92 | 26 | 0 | 0 |
| Phase 1: Received Initially Placebo, ARCT-154 D92-EOS | 23 | 0 | 0 |
| Phase 1: Received Initially ARCT-154, Placebo D92-EOS | 0 | 67 | 0 |
| Phase 3b: Received ARCT-154 D1-92 | 0 | 8059 | 0 |
| Phase 3b: Received Placebo D1-92 | 8041 | 0 | 0 |
| Phase 3b: Received Initially Placebo, ARCT-154 D92-EOS | 7350 | 0 | 0 |
| Phase 3b: Received Initially ARCT-154, Placebo D92-EOS | 0 | 7458 | 0 |
| Phase 2: Received ARCT-154 D1-92 | 0 | 226 | 0 |
| Phase 2: Received Placebo D1-92 | 75 | 0 | 0 |
| Phase 3a: Received ARCT-154 D1-92 | 0 | 448 | 0 |
Reasons for not completing this period:
| Reason | Placebo | ARCT-154 | Astra Zeneca COVID-19 vaccine |
|---|---|---|---|
| Adverse Event | 2 | 1 | 0 |
| Withdrawal by Subject | 1052 | 1006 | 20 |
| Death | 25 | 17 | 4 |
| Lost to Follow-up | 11 | 24 | 3 |
| Physician Decision | 1 | 1 | 0 |
| Other than Specified | 2 | 1 | 0 |
Analysis population for the primary outcome, as defined in the registry: Reactogenicity Analysis Set, all participants who received any dose of study vaccine (ARCT-154 or placebo or ChAdOx1) and provided at least 1 reactogenicity diary report. As pre-specified, data are presented pooled per treatment received for Phase 1/2/3a/3b, and separately for ARCT-154 for Phase 3c. Overall number of participants analyzed = number of participants evaluable for the endpoint. Number analyzed = number of participants with evaluable data at the specified timepoint.
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 Analysis Set, which included all participants who received any dose of study vaccine (ARCT-154 or placebo or ChAdOx1). As pre-specified, data were collected and are reported according to the initial study vaccine received, pooled per treatment received for Phase 1/2/3a/3b (ARCT-154/placebo), and separately for ChAdOx1 and ARCT-154 for Phase 3c. Participants are counted only once, baseline data were collected and are reported based on initial treatment received.
| Characteristic | Unit | ARCT-154 | Placebo | Phase 3c: ARCT-154 | Astra Zeneca COVID-19 vaccine | Total |
|---|---|---|---|---|---|---|
| Participants analysed | 8807 | 8294 | 1186 | 1180 | 19467 | |
| Age, Continuous | Years | 47.0 (37.0 to 57.0) | 48.0 (37.0 to 57.0) | 52.0 (42.0 to 61.0) | 52.0 (41.0 to 61.0) | 48.0 (37.0 to 57.0) |
| Sex: Female, Male: Female | Participants | 4441 | 4206 | 603 | 613 | 9863 |
| Sex: Female, Male: Male | Participants | 4366 | 4088 | 583 | 567 | 9604 |
| Race/Ethnicity, Customized: The Kinh | Participants | 8757 | 8239 | 1185 | 1177 | 19358 |
| Race/Ethnicity, Customized: Other | Participants | 50 | 55 | 1 | 3 | 109 |
6. Primary Endpoint
The registry lists the primary outcome as Number of Participants Reporting Solicited Local Adverse Reactions (ARs), measured over Within 7 days after Dose 1 and Dose 2 (up to Day 7 and 36).
| Element | Registry entry |
|---|---|
| Result type | Count Of Participants |
| Measure of spread | not applicable |
| Unit | Participants |
| Endpoint classification | Binary Endpoint |
The primary endpoint is the number of participants reporting solicited local adverse reactions. The listed reactions are injection site erythema, injection site pain, injection site induration or swelling, and injection site tenderness. The assessment window is within 7 days after Dose 1 and Dose 2, with the record giving the timeframe as up to Day 7 and Day 36.
Solicited reactions are symptoms or signs actively requested for reporting, rather than a collection limited to events that participants spontaneously mention. Counting participants with a reaction gives a binary outcome for each participant: they either meet the endpoint definition within the specified assessment window or they do not. This can make group results easier to interpret as event counts, provided the numbers assessed and the endpoint rules are clear.
The endpoint is used to describe short-term local reactogenicity after vaccination. It does not, on its own, measure immune response, prevention of infection, severe COVID-19, or the full safety profile. The registry directs readers to the Reported Adverse Events module for serious and other non-serious adverse events regardless of causality. A primary-endpoint comparison would require the corresponding group results and a defined analysis; a numerical comparison is not reported in the registry record.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry defines a clinically understandable primary outcome and gives its assessment window and analysis population. But the record does not report a single numerical comparison for that primary outcome in the information. There is consequently no primary-endpoint effect estimate, confidence interval, or p-value to interpret. Without those quantities, the direction, magnitude and precision of a between-group difference in solicited local reactions cannot be characterized from the primary endpoint.
The adverse-event record does contain counts for serious events and other events across specified groups and time periods. Those data answer a different question from the primary endpoint. In Phases 1, 2, 3a and 3b during Day 1-92, the ARCT-154 group has 133 participants with a serious event among 8807 at risk, and the placebo group has 217 among 8294 at risk. For the period from Day 92 to the end of study (Day 394), the record gives separate groups described as placebo or ARCT-154 and ARCT-154. These groups should be read using their recorded labels and periods, not treated as though they were a single continuous comparison with the earlier groups.
Phase 3c is reported separately. During Day 1-92, the record lists 22 participants with a serious event among 1186 at risk for ARCT-154, and 35 among 1180 at risk for Astra Zeneca COVID-19 vaccine. During Day 92 to the end of study (Day 394), it lists 64 among 1171 for ARCT-154 and 53 among 1168 for the comparator. These are descriptive counts with their recorded denominators; they do not establish a causal difference. No adjusted estimate or uncertainty interval for these comparisons is reported in the registry record.
The listed deaths are also counts within the adverse-event groups and periods. They should not be interpreted as evidence of treatment causation. Likewise, the record’s listed serious-event terms and percentages describe reported events; they do not replace a comparison of risks or a formal assessment of causality. The adverse-event counts do not supply the missing primary endpoint results.
Overall, the available numerical information supports a description of reported serious-event counts by recorded group and period. It does not permit a complete statistical interpretation of the solicited local-reaction endpoint, the immunogenicity outcomes, or the study’s efficacy objectives. A statistical conclusion about those outcomes would require results and methods that are not reported in the registry record.
9. Statistical Methods Explained
The record describes a randomized parallel design. In general, randomization is intended to make treatment groups comparable on average with respect to factors that could affect outcomes. It does not guarantee that every characteristic will be balanced, and it does not remove the need to define the population and outcome used in an analysis. The registry calls the study triple-masked and also describes it as observer-blind. Which roles were masked, and how masking was maintained across the different study parts, are not reported in the registry record.
How should the primary outcome be understood?
The primary endpoint counts participants reporting one or more of the specified local reactions during the stated post-dose windows. This is a binary outcome at the participant level. General statistical practice for a binary outcome is to report the number meeting the definition, the number assessed, and a comparison between groups with an uncertainty interval. A count alone cannot show how common an outcome was among those assessed, and a comparison without an uncertainty interval does not convey its precision. The registry record does not report a single primary-outcome comparison estimate.
The analysis population is also important. The record defines the reactogenicity analysis set as participants who received any dose of study vaccine and provided at least one reactogenicity diary report. This is not automatically the same population as everyone randomized or enrolled. Requiring a diary report makes the endpoint dependent on available reporting. The number with missing diaries and the handling of incomplete diary information are not reported in the registry record.
Why do time periods and study parts matter?
The endpoint is assessed after Dose 1 and Dose 2, and the record identifies time points through Day 7 and Day 36. A participant may have a different reporting opportunity after each dose. General analysis should therefore preserve the specified endpoint definition and time windows rather than combine them without justification. The registry notes that primary outcome data have several categories or time points and are not reduced to one comparison. How any category-specific results were analyzed is not reported in the registry record.
The study also contains different phases, populations and comparators. The earlier parts include ARCT-154 and placebo, while Phase 3c includes ARCT-154 and Astra Zeneca COVID-19 vaccine. The adverse-event record separately labels groups by phase and follow-up period. Such groups should not be pooled casually: group composition, treatment exposure and observation time may differ. The record’s labels are necessary context for reading the reported counts, but do not by themselves establish that the groups are directly comparable for every purpose.
What does uncertainty mean?
General statistical explanation: a confidence interval gives a range of values compatible with the observed data under the analysis assumptions. A narrow interval indicates greater precision than a wide interval, while an interval that includes no difference does not establish that the groups are identical. The registry record does not report confidence intervals or a primary endpoint effect estimate in the information. A p-value, if reported, would address compatibility with a specified null model; it would not measure clinical importance or the probability that a hypothesis is true. No primary endpoint p-value is reported in the registry record.
For binary outcomes, the chosen comparison could be expressed using a difference in proportions, a ratio, or another measure. Each has a distinct interpretation, and the estimate should be read with its uncertainty and analysis population. The statistical measure selected for the primary endpoint is not reported in the registry record. No new comparison can be calculated from the available primary endpoint information because the endpoint group results are absent.
How should planning calculations be read?
The stated sample-size assumptions describe planning illustrations based on an observed effect, not the trial’s own design justification. They specify a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation; the effect to detect is described as a stated fraction of the observed effect. For time-to-event calculations, the stated output is total events using the Schoenfeld method; other calculations are expressed as participants per arm. These planning illustrations are not observed power and do not establish that a study had a particular probability of detecting an effect. The trial’s own sample-size justification is not reported in the registry record.
General statistical explanation: over-dispersion matters when count data vary more than a chosen model expects. If ignored, the resulting uncertainty can be understated. The primary outcome is described as a count of participants with an event, rather than a repeated-event count, and no dispersion parameter or model for the primary endpoint is reported in the registry record. This is another reason not to infer an analysis method from the outcome label alone.
The record lists 17 outcome measures and zero analyses. That makes it especially important to distinguish outcome definitions from numerical findings: the presence of named outcomes does not establish that estimates, uncertainty intervals, or inferential tests are available for them in the registry record.
10. Multiplicity, Missing Data and Analysis Populations
The study includes several outcome domains and multiple listed measures. These include local reactions, serious COVID-19, antibody titres, fold rises, antibody concentrations and seroconversion. The primary endpoint itself has more than one category or time point, as noted in the record. When many outcomes or comparisons are tested, the chance of at least one apparently unusual result can increase. General methods for addressing this include prespecifying a hierarchy, adjusting significance thresholds, or treating some analyses as exploratory. The registry record does not report which approach, if any, was used.
The statistical analysis plan, including any prespecified hypotheses and handling of multiple comparisons, is not reported in the registry record. The number and purpose of interim analyses are also not reported in the registry record. No particular analysis strategy should be inferred from the list of outcomes or from the study’s randomized design.
Missing-data procedures are not reported in the registry record. For the reactogenicity analysis set, the endpoint description requires at least one diary report, but it does not state how partial diaries, missed assessments, or withdrawals were handled. The extent and pattern of missing data are not reported. This matters because participants with more complete reporting may differ from participants with incomplete reporting; the direction or magnitude of any resulting bias cannot be determined from the record.
Analysis populations are described only in part. The primary endpoint’s reactogenicity set is defined, and the record says results are pooled by treatment received for Phases 1, 2, 3a and 3b, with ARCT-154 reported separately for Phase 3c. Definitions for other outcome populations and the full analysis sets are not reported in the registry record. These omissions limit assessment of how participants were assigned to analyses and whether the intended comparisons were preserved.
11. Safety Results
The registry reports serious adverse events as affected participants divided by participants at risk.
| Arm | Participants with serious adverse events | Participants at risk | Percentage |
|---|---|---|---|
| Phases 1, 2, 3a, 3b: ARCT-154 Day 1-92 | 133 | 8807 | 1.5% |
| Phases 1, 2, 3a, 3b: Placebo Day 1-92 | 217 | 8294 | 2.6% |
| Phases 1, 2, 3a, 3b: Placebo or ARCT-154 Day 92-End of Study (Day 394) | 180 | 8161 | 2.2% |
| Phases 1, 2, 3a, 3b: ARCT-154 Day 92-End of Study (Day 394) | 176 | 7582 | 2.3% |
| Phase 3c: ARCT-154 Day 1-92 | 22 | 1186 | 1.9% |
| Phase 3c: Astra Zeneca COVID-19 vaccine Day 1-92 | 35 | 1180 | 3.0% |
| Phase 3c: ARCT-154 Day 92- End of Study (Day 394) | 64 | 1171 | 5.5% |
| Phase 3c: Astra Zeneca COVID-19 vaccine Day 92-End of Study (Day 394) | 53 | 1168 | 4.5% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Phases 1, 2, 3a, 3b: ARCT-154 Day 1-92 | 5 of 8807 |
| Phases 1, 2, 3a, 3b: Placebo Day 1-92 | 16 of 8294 |
| Phases 1, 2, 3a, 3b: Placebo or ARCT-154 Day 92-End of Study (Day 394) | 12 of 8161 |
| Phases 1, 2, 3a, 3b: ARCT-154 Day 92-End of Study (Day 394) | 9 of 7582 |
| Phase 3c: ARCT-154 Day 1-92 | 0 of 1186 |
| Phase 3c: Astra Zeneca COVID-19 vaccine Day 1-92 | 1 of 1180 |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 1% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Phases 1, 2, 3a, 3b: ARCT-154 Day 1-92 | 1303 of 8807 |
| Phases 1, 2, 3a, 3b: Placebo Day 1-92 | 1489 of 8294 |
| Phases 1, 2, 3a, 3b: Placebo or ARCT-154 Day 92-End of Study (Day 394) | 1618 of 8161 |
| Phases 1, 2, 3a, 3b: ARCT-154 Day 92-End of Study (Day 394) | 1374 of 7582 |
| Phase 3c: ARCT-154 Day 1-92 | 0 of 0 |
| Phase 3c: Astra Zeneca COVID-19 vaccine Day 1-92 | 0 of 0 |
Most frequent serious adverse event terms
| Event term | Organ system | Phases 1, 2, 3a, 3b: ARCT-154 Day 1-92 | Phases 1, 2, 3a, 3b: Placebo Day 1-92 | Phases 1, 2, 3a, 3b: Placebo or ARCT-154 Day 92-End of Study (Day 394) | Phases 1, 2, 3a, 3b: ARCT-154 Day 92-End of Study (Day 394) | Phase 3c: ARCT-154 Day 1-92 | Phase 3c: Astra Zeneca COVID-19 vaccine Day 1-92 |
|---|---|---|---|---|---|---|---|
| COVID-19 | Infections and infestations | 50 of 8807 | 139 of 8294 | 13 of 8161 | 17 of 7582 | 5 of 1186 | 8 of 1180 |
| Vestibular disorder | Ear and labyrinth disorders | 3 of 8807 | 5 of 8294 | 11 of 8161 | 9 of 7582 | 0 of 1186 | 4 of 1180 |
| Appendicitis | Infections and infestations | 4 of 8807 | 2 of 8294 | 6 of 8161 | 8 of 7582 | 0 of 1186 | 1 of 1180 |
| Pneumonia | Infections and infestations | 2 of 8807 | 5 of 8294 | 5 of 8161 | 5 of 7582 | 0 of 1186 | 0 of 1180 |
| Gastritis | Gastrointestinal disorders | 2 of 8807 | 6 of 8294 | 4 of 8161 | 2 of 7582 | 0 of 1186 | 0 of 1180 |
| Pancreatitis acute | Gastrointestinal disorders | 1 of 8807 | 1 of 8294 | 1 of 8161 | 5 of 7582 | 1 of 1186 | 0 of 1180 |
| Cerebral infarction | Nervous system disorders | 3 of 8807 | 0 of 8294 | 3 of 8161 | 2 of 7582 | 1 of 1186 | 0 of 1180 |
| Bronchitis | Infections and infestations | 0 of 8807 | 2 of 8294 | 4 of 8161 | 2 of 7582 | 0 of 1186 | 0 of 1180 |
| Lung neoplasm malignant | Neoplasms benign, malignant and unspecified (incl cysts and polyps) | 2 of 8807 | 0 of 8294 | 4 of 8161 | 2 of 7582 | 0 of 1186 | 0 of 1180 |
| Myocardial ischaemia | Cardiac disorders | 2 of 8807 | 0 of 8294 | 2 of 8161 | 3 of 7582 | 0 of 1186 | 0 of 1180 |
Most frequent non-serious adverse event terms
| Event term | Organ system | Phases 1, 2, 3a, 3b: ARCT-154 Day 1-92 | Phases 1, 2, 3a, 3b: Placebo Day 1-92 | Phases 1, 2, 3a, 3b: Placebo or ARCT-154 Day 92-End of Study (Day 394) | Phases 1, 2, 3a, 3b: ARCT-154 Day 92-End of Study (Day 394) | Phase 3c: ARCT-154 Day 1-92 | Phase 3c: Astra Zeneca COVID-19 vaccine Day 1-92 |
|---|---|---|---|---|---|---|---|
| COVID-19 | Infections and infestations | 56 of 8807 | 123 of 8294 | 1199 of 8161 | 1006 of 7582 | n/a of 0 | n/a of 0 |
| Hypertension | Vascular disorders | 349 of 8807 | 323 of 8294 | 291 of 8161 | 261 of 7582 | n/a of 0 | n/a of 0 |
| Headache | Nervous system disorders | 281 of 8807 | 285 of 8294 | 0 of 8161 | 0 of 7582 | n/a of 0 | n/a of 0 |
| Tachycardia | Cardiac disorders | 113 of 8807 | 96 of 8294 | 128 of 8161 | 107 of 7582 | n/a of 0 | n/a of 0 |
| Influenza | Infections and infestations | 201 of 8807 | 188 of 8294 | 0 of 8161 | 0 of 7582 | n/a of 0 | n/a of 0 |
| Cough | Respiratory, thoracic and mediastinal disorders | 128 of 8807 | 141 of 8294 | 0 of 8161 | 0 of 7582 | n/a of 0 | n/a of 0 |
| Arthralgia | Musculoskeletal and connective tissue disorders | 125 of 8807 | 132 of 8294 | 0 of 8161 | 0 of 7582 | n/a of 0 | n/a of 0 |
| Pharyngitis | Infections and infestations | 106 of 8807 | 110 of 8294 | 0 of 8161 | 0 of 7582 | n/a of 0 | n/a of 0 |
| Oropharyngeal pain | Respiratory, thoracic and mediastinal disorders | 67 of 8807 | 91 of 8294 | 0 of 8161 | 0 of 7582 | n/a of 0 | n/a of 0 |
| Toothache | Gastrointestinal disorders | 0 of 8807 | 0 of 8294 | 0 of 8161 | 0 of 7582 | n/a of 0 | n/a of 0 |
Serious events with the highest arm-level rate: covid-19 (1.7%), pneumonia (0.6%), vestibular disorder (0.3%), bronchitis (0.3%), nephrolithiasis (0.3%).
The serious adverse-event figures are participant counts with the corresponding number at risk, separated by recorded group and follow-up period. For example, during Day 1-92 in Phases 1, 2, 3a and 3b, the record reports 133 participants with a serious event among 8807 at risk in the ARCT-154 group, and 217 among 8294 at risk in the placebo group. For Phase 3c during the same period, it reports 22 among 1186 for ARCT-154 and 35 among 1180 for Astra Zeneca COVID-19 vaccine.
Later follow-up is reported separately, from Day 92 to the end of study (Day 394), with group labels that differ by study part. These counts should be interpreted within those labels and periods rather than combined across follow-up periods. The record also reports deaths by group and period; a death count does not establish that the vaccine caused the death. The registry’s adverse-event information does not provide a causal assessment for each event in these summaries.
These figures are descriptive. They are not adjusted comparisons, and no confidence intervals or formal between-group tests are reported in the registry record. The listed percentages for serious-event terms describe those terms as recorded, but should not be read as a complete ranking of risk or as evidence of causation. Serious-event counts also do not answer the primary question about solicited local reactions, which has a different definition and assessment window.
12. What the Result Does, and Does Not, Mean
The registry record establishes that ARCT-154 was studied in a randomized, controlled programme with safety, immunogenicity and efficacy objectives. It also defines a primary endpoint for solicited local adverse reactions and an analysis population based on receipt of a dose and diary reporting. These details clarify what the primary endpoint was intended to measure.
The record does not report a single numerical primary endpoint comparison in the information. Consequently, no conclusion about the size, direction or precision of a difference in local reactions can be drawn from those primary endpoint details alone. The same caution applies to the listed immunogenicity and efficacy outcomes: their names indicate what was to be assessed, not what the results were. The record’s secondary outcome list includes antibody measures and first occurrence of severe COVID-19, but numerical estimates for those outcomes are not reported.
The adverse-event module supplies descriptive serious-event counts across groups and follow-up periods. Those counts are useful for understanding what was recorded, but they do not establish that treatment caused or prevented an event, and they are not adjusted comparisons. Differences in counts across groups cannot be interpreted without considering the group definitions, denominators, observation periods and uncertainty. No causal conclusion should be drawn from the counts alone.
In general, a trial result is best interpreted by combining the estimated effect, its precision, the outcome definition, the analysis population and the design. The registry record contains some design and outcome definitions but does not report the primary estimate and uncertainty needed for that interpretation. The appropriate statistical conclusion is therefore limited: the record describes the study and reports selected adverse-event counts, while the primary comparative result and several analysis details are not reported in the registry record.
13. Why This Trial Matters Statistically
This study is statistically notable for its multi-part structure. It includes placebo-controlled parts and a Phase 3c active-comparator part, as well as different objectives spanning safety, immunogenicity and efficacy. That structure makes clear reporting of phase-specific populations, treatment groups, endpoints and follow-up especially important. The registry’s separate labels for the adverse-event groups help preserve some of that context.
The primary endpoint is a solicited participant-level outcome with specified reactions and post-dose windows. Its definition illustrates why outcome details matter: a count of participants depends on what qualifies as a reaction, when it is assessed, and which participants contribute data. The specified reactogenicity set requires both receipt of a study dose and at least one diary report, linking the endpoint to reporting completeness.
The record also illustrates the distinction between an outcome definition and an outcome result. A detailed endpoint description does not substitute for an estimate, uncertainty interval or prespecified analysis. Here, a single primary comparison estimate is not reported in the registry record, while serious-event counts are available for defined periods. Keeping these forms of evidence separate prevents descriptive safety counts from being mistaken for a result on the primary endpoint or for an efficacy estimate.
Finally, the programme’s multiple outcomes and time points make transparency about multiplicity, missing data and analysis populations important for statistical interpretation. Those methods are not reported in the registry record. The case therefore underscores a general reporting principle: readers need both the clinical definitions and the analysis details to judge what a numerical result supports, and need numerical results with uncertainty to assess its precision.
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 central limitation is that the registry record does not report a single comparative estimate for the primary solicited local adverse-reaction endpoint in the information. The endpoint definition and assessment timeframe are available, but the group-level primary outcome results and their precision are not. This prevents a quantitative interpretation of the primary question.
The study spans several parts, phases, populations and comparators. The record describes pooling by treatment received for Phases 1, 2, 3a and 3b and separate ARCT-154 data for Phase 3c for the primary outcome. It does not provide a single aligned comparison across all parts. Comparisons should therefore be kept within the recorded group definitions, rather than assuming that populations or follow-up are interchangeable.
Important analytic details are not reported in the registry record, including the statistical plan, multiplicity handling, missing-data methods, interim analyses, and the full definitions of analysis populations for outcomes beyond the primary endpoint. The number of participants with incomplete diary data and the treatment of partial reporting are also not reported. These gaps limit assessment of potential bias and of whether the analysis followed prespecified methods.
The adverse-event data are descriptive counts by group and period. The registry record does not report adjusted comparisons or uncertainty intervals for those counts, and the reported summaries do not establish causality. The serious-event counts should not be treated as a substitute for the missing primary endpoint comparison or for efficacy results.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: The ARCT-154 Self-Amplifying RNA Vaccine Efficacy Study (ARCT-154-01) — NCT05012943.
- Registry record last updated 2025-11-06; status last verified 2025-10.
- Results first posted 2025-11-06.
- 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.
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18. Record Summary
NCT05012943 is a completed randomized, parallel, triple-masked study of ARCT-154 with placebo and Astra Zeneca COVID-19 vaccine listed as interventions. The registry describes a multi-part study in adults in Vietnam, with safety, immunogenicity and efficacy objectives. Total enrollment is 19474.
The primary endpoint counts participants reporting solicited local adverse reactions within the specified post-dose windows. The registry defines the reactogenicity analysis set and describes pooled reporting for Phases 1, 2, 3a and 3b, with ARCT-154 reported separately for Phase 3c. A single numerical primary comparison is not reported in the registry record. Selected serious-event counts are reported by group and follow-up period, but no adjusted comparison or uncertainty interval is reported for them.
The registry lists 17 outcome measures and zero analyses. Details on multiplicity, missing-data handling, and the statistical analysis plan are not reported in the registry record. The available information supports a description of the design, endpoint definitions and selected adverse-event counts, but not a complete statistical interpretation of the primary endpoint or other named outcomes.