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 NDV-HXP-S Vaccine Clinical Trial (COVIVAC) (NCT05940194), a randomized phase 2 study. The primary outcome is Percentage of Participants With Local and Systemic Solicited AEs by Severity During the First 7 Days After Each Vaccination..
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT05940194 |
| Phase | Phase 2 |
| Condition | COVID-19 |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | Triple |
| Enrollment | 374 |
| Arms in the primary outcome | n/a |
| Lead sponsor | Institute of Vaccines and Medical Biologicals, Vietnam |
| Results posted | Yes |
2. Clinical Question
Population
The combined study concerns adults in Vietnam. Its official title describes adults aged ≥ 18 and ≥ 60 years old, while the Phase 2 summary describes adults aged 18-75 years. The primary endpoint population is described as all participants who received at least one vaccination.
Intervention
Phase 2 evaluated COVIVAC at 3 mcg and 6 mcg. Both were described as intramuscular vaccinations given in two doses, with each dose 28 days apart from the other.
Comparator
The active comparator was AZD1222, described as AstraZeneca vaccine. It was also given intramuscularly in two doses 28 days apart. The Phase 1 portion is described as placebo-controlled, but the Phase 2 comparison is active-controlled.
Primary question
The primary endpoint asks what percentage of participants experienced solicited local or systemic adverse events, classified by severity, during the first 7 days after each vaccination. The registry record does not report the endpoint results or analyses, so it does not establish how the groups compared on this safety measure.
3. Trial Design
The registry describes a prospective, randomized, observer-blind Phase 1/2 study at a single center in Vietnam. Its listed phase is Phase 2, while the title and study summary describe the combined Phase 1/2 program. The registry reports that the trial started on 2021-08-11, reached primary completion on 2021-10-18, and has completed status.
The study had two separate parts. The Phase 1 part is described as placebo-controlled. After a Phase 1 interim analysis, 3 mcg and 6 mcg COVIVAC doses were selected for Phase 2. The Phase 2 part is described as active-controlled, with participants randomized among AZD1222, COVIVAC 3 mcg, and COVIVAC 6 mcg. The registry enrollment is 374, and the summary describes a 1:1:1 allocation for Phase 2.
All three Phase 2 regimens were described as intramuscular injections administered as two doses of 0.5mL, 28 days apart. The registry lists triple masking and a parallel model. It does not explain which roles were masked or provide further implementation details, so those should not be inferred from the masking label alone.
The Institute of Vaccines and Medical Biologicals, Vietnam, is listed as sponsor. The design provides a framework for comparing safety and immunogenicity across active vaccine groups, but the design description is not itself evidence about outcome differences. The record does not report the Phase 2 randomization sequence, concealment procedures, or a statistical analysis plan.
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: This is the phase 2 (part 2) of the phase 1/2 trial of COVIVAC vaccine. After providing informed consent, participants were screened and then randomized to receive either of 2 COVIVAC dose or AZD1222 in the 1:1:1 ratio. Each participant received 2 injections with 28 days apart.
Overall Study
| Stage | COVIVAC 3 mcg | COVIVAC 6 mcg | AZD1222 |
|---|---|---|---|
| STARTED | 124 | 125 | 125 |
| COMPLETED | 122 | 122 | 121 |
| NOT COMPLETED | 2 | 3 | 4 |
Reasons for not completing this period:
| Reason | COVIVAC 3 mcg | COVIVAC 6 mcg | AZD1222 |
|---|---|---|---|
| Adverse Event | 0 | 1 | 0 |
| Migrated/Moved from the study area | 2 | 2 | 4 |
Analysis population for the primary outcome, as defined in the registry: All participants received at least one vaccination.
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.
| Characteristic | Unit | COVIVAC 3 mcg | COVIVAC 6 mcg | AZD1222 | Total |
|---|---|---|---|---|---|
| Participants analysed | 124 | 125 | 125 | 374 | |
| Age, Continuous | Years | 48.9 (SD 14.82) | 48.9 (SD 14.27) | 49.8 (SD 14.17) | 49.2 (SD 14.39) |
| Sex: Female, Male: Female | Participants | 60 | 58 | 71 | 189 |
| Sex: Female, Male: Male | Participants | 64 | 67 | 54 | 185 |
| Race/Ethnicity, Customized: Kinh | Participants | 124 | 124 | 125 | 373 |
| Race/Ethnicity, Customized: Other | Participants | 0 | 1 | 0 | 1 |
| BMI | kg/m^2 | 22.29 (SD 2.67) | 22.27 (SD 2.52) | 22.24 (SD 2.55) | 22.27 (SD 2.57) |
6. Primary Endpoint
The registry lists the primary outcome as Percentage of Participants With Local and Systemic Solicited AEs by Severity During the First 7 Days After Each Vaccination., measured over 7 days after each vaccination.
| Element | Registry entry |
|---|---|
| Result type | Number |
| Measure of spread | 95% Confidence Interval |
| Unit | percent of participants |
| Endpoint classification | Binary Endpoint |
The primary endpoint is the percentage of participants with solicited local and systemic adverse events, categorized by severity, during the first 7 days after each vaccination. Local events listed are pain or tenderness, swelling or induration, and erythema. Systemic events listed are fever, headache, fatigue or malaise, myalgia, arthralgia, and nausea or vomiting. Fever is defined as oral temperature ≥ 38°C.
Severity is defined by the effect on daily activities and whether intervention is indicated. Mild events cause no or minimal interference and do not indicate intervention. Moderate events interfere with, but do not prevent, normal daily activities, and intervention is indicated. Severe events prevent normal daily activities, with intervention or hospitalization indicated.
This endpoint is used to describe short-term reactogenicity after vaccination: the frequency and severity of symptoms actively solicited during the specified period. Reporting percentages with confidence intervals can communicate both the observed frequency and the precision of its estimate. The record specifies a 95% confidence interval, but does not report endpoint values or intervals. It therefore does not show the observed percentage in any group or the precision of a between-group comparison.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record identifies the primary safety question and the groups intended for comparison, but it does not report the primary endpoint results. In particular, it gives no percentages of participants with solicited local or systemic adverse events by severity, and no confidence interval estimates for those percentages. The posted record therefore does not support a conclusion about which Phase 2 group had more or fewer of these events, or about the size or precision of any difference.
The record lists 12 outcome measures and 0 analyses. Secondary outcomes include anti-S IgG geometric mean concentrations at 14 Days and 6 Months After Second Vaccination, geometric mean fold rises at those times, and the percentage with seroresponses at those times. These outcome descriptions identify what was planned for assessment; they are not results. No immunogenicity estimates or comparative analyses are reported in the registry record.
Randomization is intended to support fair comparisons by assigning participants to groups rather than letting treatment choice determine group membership. General statistical interpretation: randomization can reduce systematic differences between groups at baseline, but it does not guarantee identical groups, and it cannot compensate for unreported outcome data or analysis methods. Observer blinding may reduce some forms of assessment bias, but the record does not explain who was masked or how masking was maintained.
The record also lists adverse-event counts separately from the missing primary endpoint analysis. Those counts describe serious and other adverse events in the registry's safety summary, but they are not a substitute for the primary endpoint. The primary endpoint concerns solicited events by severity during the first 7 days after each vaccination. The safety summary does not provide that complete breakdown or its confidence intervals.
A clinical interpretation should distinguish the study's completed status from the completeness of its posted results. Completion indicates the trial's registry status, not that all planned endpoints or statistical analyses are reported. Without the stated primary endpoint estimates, confidence intervals, and an analysis description, the registry record cannot establish the comparative frequency or severity of solicited events. It also cannot support claims about efficacy or overall safety beyond the limited event counts it lists.
9. Statistical Methods Explained
What kind of endpoint is this?
The primary endpoint is a percentage of participants with an event, so it is a binary-outcome summary at the participant level: a participant either meets the event definition for a specified category and period or does not. The registry describes the endpoint as a percentage and specifies a 95% confidence interval. It does not report the actual percentages, their intervals, or the statistical procedure used to calculate them.
General: a confidence interval expresses uncertainty around an estimate under the assumptions of the calculation method. A narrower interval indicates greater precision under those assumptions; a wider interval indicates less precision. It is not a guarantee that the true value lies in the interval, and it does not by itself establish whether a difference is important. Because no intervals are posted for the primary endpoint, its precision cannot be judged from the registry record.
Why report severity and timing?
The endpoint specifies local and systemic symptom categories, severity grades, and the first 7 days after each vaccination. Those distinctions matter because an overall event percentage could conceal differences between types of symptoms or degrees of interference with daily activities. The record specifies that mild, moderate, and severe events have different definitions. It does not give the observed counts or percentages within those categories, nor does it provide a combined estimate that could be interpreted as covering every category and time point.
General: repeated observation periods and multiple event categories can create several related summaries. A clear analysis should state how events are counted, whether participants with more than one event contribute to more than one category, and how results across periods are presented. Those details are not reported in the registry record. The listed endpoint should therefore be read as a description of what was to be measured, not as a fully specified calculation rule.
What can randomization contribute?
The Phase 2 design is described as randomized, parallel, and active-controlled, with three vaccine groups. The study summary gives a 1:1:1 allocation. General: random allocation is intended to make treatment assignment independent of participant characteristics, which supports interpretation of group comparisons. It does not ensure equal baseline characteristics in a particular trial, and the registry record does not report baseline data or the allocation procedure. No statistical model or adjustment strategy is identified.
The registry labels masking as triple and the trial as observer-blind. General: masking can limit the influence of knowledge about assignment on participant reporting, clinical observation, or other study processes. The registry does not identify the masked roles or describe how masking was maintained, so the label alone cannot establish which potential sources of bias were addressed.
What analysis details are available?
The registry record lists 12 outcome measures and 0 analyses. It gives a primary endpoint definition and specifies a 95% confidence interval, but does not report a statistical analysis plan, hypothesis tests, model choice, missing-data handling, or analysis-population rules beyond the primary endpoint population being all participants who received at least one vaccination. The record does mention a Phase 1 interim analysis as part of the process for selecting doses for Phase 2; it does not describe that analysis's methods or results.
General: for an event percentage, the calculation depends on the event definition, the participants included in the denominator, and the handling of missing observations. When results are compared between groups, the estimate of the difference and its uncertainty are often more informative than separate group percentages alone. No comparative estimate or test is reported in the registry record. Any choice of model, adjustment, or missing-data assumption beyond what the record states would be speculation.
What do the planning assumptions mean?
The registry describes a planning illustration based on the observed effect, using a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. It says the effect to detect is a stated fraction of the observed effect. These are assumptions for a planning illustration, not a description of the trial's own design justification. The registry record does not report a sample-size justification for the trial, and the planning illustration should not be described as observed power.
General: a planning calculation estimates how much information a future study might need under its assumptions. Its output depends on the assumed effect, variability, allocation, and analysis method. If assumptions change, the planning result can change. A calculation based on an observed effect is particularly dependent on that estimate and should not be treated as proof that a completed trial was adequately powered. The record does not give a reported primary endpoint effect or analysis from which the trial's achieved precision could be assessed.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists 12 outcome measures. The primary endpoint includes multiple local and systemic event categories, severity levels, and observation after each vaccination. Secondary outcomes include anti-S IgG geometric mean concentrations, geometric mean fold rises, and seroresponse percentages at 14 Days and 6 Months After Second Vaccination. This range of outcomes and time points creates multiple opportunities to examine results.
Multiplicity refers generally to the increased chance of at least one apparently unusual result when many statistical tests are performed. A prespecified approach may identify a primary comparison, control the interpretation of secondary comparisons, or adjust for multiple testing. The registry record does not report a multiplicity strategy, a hierarchy among secondary outcomes, or inferential analyses. No p-values or comparative outcome analyses are listed.
The record describes the primary endpoint population as all participants who received at least one vaccination. It does not specify the analysis population for the other outcomes, or how missing measurements, withdrawal, or incomplete follow-up were handled. Missing-data methods are not reported in the registry record. The number of outcome measures alone cannot establish which outcomes were fully observed or included in an analysis.
The Phase 1 interim analysis is mentioned in connection with selecting COVIVAC doses for Phase 2. Its timing, statistical methods, and any implications for later inference are not reported in the registry record. That mention should not be treated as evidence of an interim analysis plan for the Phase 2 outcome comparisons.
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 |
|---|---|---|---|
| COVIVAC 3 mcg | 5 | 124 | 4.0% |
| COVIVAC 6 mcg | 3 | 125 | 2.4% |
| AZD1222 | 0 | 125 | 0.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| COVIVAC 3 mcg | 0 of 124 |
| COVIVAC 6 mcg | 0 of 125 |
| AZD1222 | 0 of 125 |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 5% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| COVIVAC 3 mcg | 25 of 124 |
| COVIVAC 6 mcg | 22 of 125 |
| AZD1222 | 25 of 125 |
Most frequent serious adverse event terms
| Event term | Organ system | COVIVAC 3 mcg | COVIVAC 6 mcg | AZD1222 |
|---|---|---|---|---|
| BRAIN CONCUSSION (DUE TO TRAFFIC ACCIDENT) | Injury, poisoning and procedural complications | 1 of 124 | 0 of 125 | 0 of 125 |
| STOMACH CANCER | Neoplasms benign, malignant and unspecified (incl cysts and polyps) | 0 of 124 | 1 of 125 | 0 of 125 |
| COVID-19 | Infections and infestations | 0 of 124 | 1 of 125 | 0 of 125 |
| COLON CANCER | Neoplasms benign, malignant and unspecified (incl cysts and polyps) | 0 of 124 | 1 of 125 | 0 of 125 |
| LEUKEMIA | Neoplasms benign, malignant and unspecified (incl cysts and polyps) | 1 of 124 | 0 of 125 | 0 of 125 |
| INTESTINAL OBSTRUCTION | Gastrointestinal disorders | 1 of 124 | 0 of 125 | 0 of 125 |
| CHRONIC INFLAMMATION OF THE SALIVARY GLANDS | Gastrointestinal disorders | 1 of 124 | 0 of 125 | 0 of 125 |
| INFECTION AFTER SURGERY | Injury, poisoning and procedural complications | 1 of 124 | 0 of 125 | 0 of 125 |
Most frequent non-serious adverse event terms
| Event term | Organ system | COVIVAC 3 mcg | COVIVAC 6 mcg | AZD1222 |
|---|---|---|---|---|
| Covid-19 | Infections and infestations | 25 of 124 | 22 of 125 | 25 of 125 |
Serious events with the highest arm-level rate: brain concussion (due to traffic accident) (0.8%), leukemia (0.8%), intestinal obstruction (0.8%), chronic inflammation of the salivary glands (0.8%), infection after surgery (0.8%).
The registry's serious adverse-event summary lists 5 affected participants among 124 at risk in the COVIVAC 3 mcg group, 3 among 125 in the COVIVAC 6 mcg group, and 0 among 125 in the AZD1222 group. The listed counts of other adverse events are 25 among 124, 22 among 125, and 25 among 125, respectively. The death count is 0 in each group.
The serious-event terms listed are brain concussion (due to traffic accident), leukemia, intestinal obstruction, chronic inflammation of the salivary glands, infection after surgery, and stomach cancer; each is listed as 0.8%. The registry does not provide enough detail in this summary to establish whether terms overlap within participants, how relatedness to vaccination was assessed, or the event timing. These counts and terms should not be treated as evidence that vaccination caused an event or that an event was unrelated.
These safety-summary figures are distinct from the primary endpoint, which concerns solicited events by severity during the first 7 days after each vaccination. The registry record does not report that endpoint's group results.
12. What the Result Does, and Does Not, Mean
This trial's registry record establishes the design question: in Phase 2, COVIVAC at 3 mcg and 6 mcg was compared with AZD1222 in a randomized, active-controlled study. It also defines a primary short-term safety endpoint and lists secondary immunogenicity outcomes. Those details help readers understand what the trial was intended to assess.
The record does not report analyses for the primary endpoint or the listed secondary outcomes. Therefore it does not show the percentage of participants with solicited adverse events by severity, the precision of those percentages, or whether groups differed. It also does not show antibody concentration or seroresponse results. The separate adverse-event counts give limited safety information, but they do not replace endpoint-specific comparative analyses.
General: absence of reported results is not evidence that there were no events or no differences. Likewise, the fact that an endpoint was specified does not establish that the endpoint met a particular threshold or that a vaccine had a particular effect. Interpretation requires the observed estimates, uncertainty, analysis methods, and relevant population definitions.
The listed serious-event and other-event counts should be read descriptively. The registry summary does not establish causality, comparative risk, or the clinical importance of individual events. The record also does not report enough detail to assess how missing observations, multiple outcomes, or the Phase 1 interim analysis were addressed statistically. Accordingly, conclusions should remain confined to the design and the limited safety counts recorded, rather than extending to efficacy or an overall judgment about safety.
13. Why This Trial Matters Statistically
The trial is statistically relevant because its design separates dose evaluation from the active-controlled Phase 2 comparison. The summary says that a Phase 1 interim analysis preceded selection of the 3 mcg and 6 mcg doses for Phase 2. The later comparison included those COVIVAC doses and AZD1222, with randomized allocation described as 1:1:1. This gives a clear framework for asking whether safety and immunogenicity summaries differ across active vaccine groups.
The primary endpoint also illustrates why outcome definitions matter. It does not simply count all adverse events: it specifies solicited local and systemic symptoms, severity grades, and a 7-day period after each vaccination. Those choices determine what the endpoint can describe and what it cannot. The endpoint is not a broad measure of every possible adverse event over all follow-up.
The registry record also illustrates the difference between a registered question and a reported result. It contains outcome definitions and safety counts, but lists 0 analyses. Without the endpoint estimates and their confidence intervals, a reader cannot assess comparative frequency or precision. This is an important statistical limitation even though the trial status is completed.
Finally, the trial's multiple outcomes and time points make transparent analysis methods important. The registry does not report a statistical analysis plan or multiplicity approach. Clear reporting of populations, missing data, and uncertainty would be needed to evaluate the strength and limits of any comparative claims.
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 the primary question is that the registry record does not report its endpoint results. Although it specifies solicited events, severity categories, timing, and a 95% confidence interval, it gives no corresponding percentages, event counts, or intervals by group. There is consequently no reported primary comparison to assess.
The record lists 12 outcome measures but 0 analyses. The secondary immunogenicity outcomes are described without estimates. Statistical methods for the primary or secondary outcomes, including any model, adjustment, or hypothesis-testing procedure, are not reported in the registry record. Nor does the record describe a multiplicity strategy for the outcomes and time points.
Analysis populations are incompletely described. The primary population is defined as participants who received at least one vaccination, but the record does not explain how missing outcome data, incomplete follow-up, or other analysis populations were handled. It also does not report baseline characteristics or explain the randomization and masking procedures in detail.
The Phase 1 interim analysis is mentioned as informing dose selection, but its methods and results are not described. The planning illustration assumptions are not the trial's reported design justification, and they do not supply an observed analysis of the primary endpoint. The serious-event summary is limited to counts and listed terms; it does not establish causality, timing, or comparative risk. These omissions restrict conclusions to the design description and the specific safety counts recorded.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: NDV-HXP-S Vaccine Clinical Trial (COVIVAC) — NCT05940194.
- Registry record last updated 2025-01-15; status last verified 2024-06.
- Results first posted 2025-01-15.
- 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
The registry describes a completed, randomized, observer-blind Phase 1/2 study of COVIVAC in Vietnam, sponsored by the Institute of Vaccines and Medical Biologicals, Vietnam. The Phase 2 portion compared COVIVAC 3 mcg and 6 mcg with AZD1222. Each regimen was described as two intramuscular doses 28 days apart.
The primary endpoint was the percentage of participants with solicited local and systemic adverse events by severity during the first 7 days after each vaccination. The registry specifies a 95% confidence interval but does not report the endpoint results or analyses. It lists secondary immunogenicity outcomes and limited adverse-event counts, but not analyses for the listed outcomes. Thus, the record describes the intended comparisons without reporting the primary comparative safety result.