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 Saved From COVID-19 - Chloroquine (CQ) Prophylaxis for Health Care Workers at Risk for COVID (NCT04349371), a randomized phase 2 study. The primary outcome is Number of Healthcare Workers With Symptomatic COVID Infections.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT04349371 |
| Phase | Phase 2 |
| Condition | COVID, Coronavirus Infection |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | Quadruple |
| Enrollment | 5 |
| Arms in the primary outcome | n/a |
| Lead sponsor | Columbia University |
| Results posted | Yes |
2. Clinical Question
Population
Health care workers with moderate to high risk of exposure to COVID-19. The registry record lists enrollment as 5, but also states that the trial was terminated before participants could be assigned to an arm.
Intervention
Chloroquine (CQ) prophylaxis. The arm description refers to a three-month supply and a schedule of two 250 mg tablets daily for one week, followed by two tablets for one day a week for the remainder of the study period.
Comparator
Placebo oral tablet, described as a three-month supply. The record does not provide an arm-level outcome comparison.
Primary question
Would CQ prophylaxis prevent symptomatic COVID-19 infections among health care workers at risk of exposure, compared with placebo? The planned diagnosis relied on symptoms and confirmatory anti-COVID antibodies and, when available, COVID-19 PCR.
This is a question about prevention in an occupationally exposed population, rather than treatment after illness begins. The registry also describes a secondary interest in preventing any infection, defined through seroconversion to positive anti-COVID antibody status. That distinction matters: symptomatic disease and evidence of infection are related but not identical outcomes. A person could meet a definition of infection without meeting the symptomatic primary outcome.
The record identifies the trial as randomized, quadruple-masked, and parallel-group. Those features describe the intended comparison, but they do not produce an answer when assignment and outcome assessment did not occur. The registry explicitly states that termination happened before participants could be assigned to any arm and that data were therefore not collected or analyzed. Consequently, the clinical question remains unanswered by this trial's posted results.
3. Trial Design
The registry describes a phase 2, randomized, quadruple-masked, parallel-group study sponsored by Columbia University. Its title identifies chloroquine prophylaxis for health care workers at risk for COVID, and the brief summary describes a target population with moderate to high exposure risk. The planned comparison was CQ against placebo, with the primary objective focused on symptomatic COVID-19 prevention.
The intervention descriptions refer to a three-month supply. The CQ arm description gives a schedule of two 250 mg tablets each day for one week and then two tablets for one day a week for the remaining study duration. The comparator is listed as a placebo oral tablet. These are descriptions of the planned intervention, not evidence that participants received either regimen. The registry says no participants were assigned to an arm.
The recorded study start was 2020-04-21, and the primary completion date was 2021-02-11. The status is terminated. The record lists enrollment as 5; that figure should be read alongside the statement that the study ended before arm assignment, not as evidence of an analyzed treatment group. The record does not report a completed randomized comparison.
The primary outcome was the number of health care workers with symptomatic COVID infections, with a timeframe of up to 3 months. A secondary outcome was the number of workers and patients with infections; the study summary describes secondary assessment of seroconversion to positive anti-COVID antibody status. There are two outcome measures listed, but the registry reports no analyses. It does not report an analysis population, an allocation ratio actually achieved, or outcome results by arm.
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: The study was terminated before participants could be assigned to any Arm. There were 5 participants who signed informed consent form: 3 participants withdrew, and 2 participants did not proceed due to study termination.
Overall Study
| Stage | CQ Group | Placebo Group |
|---|---|---|
| STARTED | 0 | 0 |
| COMPLETED | 0 | 0 |
| NOT COMPLETED | 0 | 0 |
Analysis population for the primary outcome, as defined in the registry: The study was terminated before participants could be assigned to any Arm. Data was therefore not collected or analyzed.
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: The study was terminated before participants could be assigned to any Arm.
| Characteristic | Unit | CQ and Placebo Group |
|---|---|---|
| Participants analysed | 0 | |
| Age, Categorical: <=18 years | — | |
| Age, Categorical: Between 18 and 65 years | — | |
| Age, Categorical: >=65 years | — | |
| Sex: Female, Male: Female | — | |
| Sex: Female, Male: Male | — | |
| Region of Enrollment: United States | participants | — |
6. Primary Endpoint
The registry lists the primary outcome as Number of Healthcare Workers With Symptomatic COVID Infections, measured over Up to 3 months.
| Element | Registry entry |
|---|---|
| Result type | N/A |
| Measure of spread | not applicable |
| Unit | not stated |
| Endpoint classification | not reduced to a single comparison |
The planned primary endpoint was the number of health care workers with symptomatic COVID infections during a timeframe of up to 3 months. The registry describes diagnosis as based on COVID-19 symptoms and confirmatory anti-COVID antibodies, with COVID-19 PCR used when available. This combines clinical illness with laboratory evidence to identify the outcome of interest.
A symptomatic endpoint addresses whether participants developed illness, rather than whether they had any evidence of infection. The registry's secondary outcome description separately refers to infections and to seroconversion to positive anti-COVID antibody status. That distinction can be useful in prevention research because an intervention might be evaluated against symptomatic disease, evidence of infection, or both; these outcome definitions answer different questions.
The endpoint was selected to evaluate the stated clinical objective of preventing symptomatic COVID-19 in health care workers at risk of exposure. However, the record says the trial was terminated before participants could be assigned to any arm. It also states that data were not collected or analyzed. Therefore, there is no observed primary endpoint count, treatment contrast, or estimate of precision to interpret. The endpoint's intended definition can be described, but the posted results cannot establish how often it occurred or whether the planned groups differed.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The key statistical fact is not an estimated effect but the absence of an analyzed comparison. The registry states that the study was terminated before participants could be assigned to any arm and that data were therefore not collected or analyzed. As a result, there is no observed primary outcome result for CQ versus placebo, no estimate of the treatment contrast, and no confidence interval or hypothesis test reported for that question.
The registry lists enrollment as 5. That record entry does not establish that participants received study treatment or contributed outcome data: the same record explicitly says arm assignment never occurred. It is therefore not appropriate to interpret the enrollment entry as a completed randomized sample or to infer an outcome rate from it. Nor can the absence of reported symptomatic cases be read as evidence that no cases occurred; the registry says the outcome data were not collected or analyzed.
The primary endpoint was intended to count health care workers with symptomatic COVID infections over up to 3 months. Its description included symptoms and confirmatory anti-COVID antibodies, with PCR when available. The secondary infection outcome involved seroconversion. Neither endpoint has a posted analyzed result. The record lists two outcome measures but zero analyses, which is consistent with the statement that the study stopped before assignment.
There is consequently no basis in the registry record for judging the direction, magnitude, or precision of a CQ effect. A confidence interval would ordinarily communicate the range of treatment differences compatible with the observed data and the statistical method. In this case, there is no posted endpoint estimate from which to interpret such a range. A p-value would likewise require an analyzed comparison and is not reported.
Planning illustrations, when displayed, should not be mistaken for evidence from this trial. A sample-size calculation is a planning exercise under specified assumptions; it does not create an observed treatment effect or demonstrate the probability that the trial would have detected one. The registry record does not report an analyzed effect for the primary endpoint, and any planning numbers cannot substitute for outcome data. They do not answer whether CQ changed the outcome.
The aggregate serious adverse event figures also cannot repair the missing efficacy comparison. They report zero serious adverse events, zero other adverse events, and zero deaths in the combined CQ and placebo group, with 5 at risk for each listed category. Because the record reports no arm assignment, those figures do not provide a randomized, arm-specific safety contrast. They should be read as the registry's aggregate entries, not as proof of comparative safety.
The appropriate conclusion is narrow: the registry documents a planned randomized comparison and its intended outcomes, but reports termination before treatment assignment and no outcome analysis. The clinical efficacy question remains unresolved in these posted results. Any stronger conclusion about prevention, infection risk, or safety would go beyond what the record reports.
9. Statistical Methods Explained
What does randomization ordinarily contribute?
In general, randomization assigns participants to study groups by chance. When it is carried out, it is intended to make the groups comparable, on average, with respect to both measured and unmeasured characteristics. This supports interpretation of a difference in outcomes as an estimate of the effect of assignment to the intervention rather than a consequence of deliberate group selection. Randomization does not guarantee identical groups, especially in small studies, and it does not replace careful outcome measurement or analysis.
The registry identifies this study as randomized and parallel-group, but also states that it ended before participants could be assigned to an arm. Thus the design label describes the planned method, not a completed random allocation. There are no treatment groups with primary outcome data to compare.
What does masking ordinarily do?
In general, masking means that specified people involved in a study do not know which intervention was assigned. It can reduce the risk that expectations affect care, participant reports, outcome assessment, or analysis decisions. The registry labels the planned study quadruple-masked. That designation does not establish that masking was implemented: with no arm assignment, the record provides no evidence of a masked treatment period or outcome assessment.
What would a treatment contrast mean?
In general, a treatment contrast compares an outcome between groups, using a defined measure such as a difference in event rates or another effect measure suited to the endpoint. For this study, a contrast would have required outcome data for the CQ and placebo groups under the planned symptomatic COVID definition. A contrast is not available merely because the registry lists two interventions. The primary outcome population description explicitly says no data were collected or analyzed after termination before assignment.
Confidence intervals are generally used to show statistical uncertainty around an estimated effect. Their width reflects the precision of the estimate under the chosen analysis, and their interpretation depends on the data and method. A narrow interval would indicate greater precision than a wide one, but neither can be formed for the primary outcome without an analyzed effect estimate. The record does not report a confidence interval or any primary-outcome estimate.
Hypothesis tests generally assess how compatible observed data are with a specified null hypothesis under a statistical model. A p-value is not a measure of clinical importance, and it cannot establish that an effect is absent. Most importantly for this record, a test requires an observed comparison and an analysis. No primary endpoint analysis is reported, so there is no trial p-value to interpret.
Why do the outcome definitions matter?
In general, outcome definitions determine what counts as an event and therefore what a trial's estimate means. The planned primary endpoint counted health care workers with symptomatic COVID infections, with diagnosis based on symptoms and confirmatory anti-COVID antibodies and, when available, COVID-19 PCR. The secondary description concerns infections, including seroconversion to positive anti-COVID antibody status. Symptomatic disease and serologic evidence are distinct endpoint concepts; results for one would not automatically answer the other.
In general, the availability of different diagnostic methods can affect how consistently outcomes are ascertained. The registry's phrase when available indicates PCR was not described as universally required. It does not report how often PCR would have been available, how discordant assessments would be resolved, or whether endpoint adjudication was planned. These details are not reported in the registry record, and no outcome data exist to assess their practical effect.
What can planning calculations tell a reader?
In general, sample-size calculations estimate the amount of information a future study may need under chosen assumptions about the effect to detect, significance level, allocation, and statistical model. The registry's planning assumptions describe a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. They also refer to detecting a stated fraction of an observed effect. Such assumptions are planning choices, not findings from an intervention comparison.
A sample-size illustration is not observed power. Observed power is not a substitute for estimating an effect and its uncertainty after data collection; in a terminated study without an analyzed primary endpoint, no empirical efficacy result can be recovered from a planning calculation. The record does not report a primary outcome effect estimate that could support a trial-specific planning interpretation. Any displayed planning values must therefore remain hypothetical illustrations rather than evidence about CQ.
For event-based outcomes, statistical methods may also depend on the number and timing of events. General methods for time-to-event endpoints use information about event occurrence and follow-up; a simple event count may not capture when events occurred or how long participants were observed. The registry's primary endpoint is described as a count within a timeframe, and it does not report an analyzed time-to-event result. There is no basis for reconstructing such an analysis.
Why does the registry's analysis count matter?
The record lists zero analyses. This means the posted registry record does not include a statistical analysis of the efficacy outcomes. In general, an analysis plan specifies how outcomes, populations, missing observations, and group comparisons will be handled. Details such as model choice, covariate adjustment, confidence-interval method, and handling of multiple outcomes are not reported in the registry record. They should not be inferred from the randomized or masked design labels.
Overall, the statistical methods that can be described are the intended design features and the general meaning of common analysis tools. There is no completed primary-outcome analysis to reproduce or interpret. The principal statistical conclusion is therefore about the limits of the evidence: the planned comparison produced no posted estimate of effect or precision.
10. Multiplicity, Missing Data and Analysis Populations
Multiplicity concerns arise when a study evaluates multiple outcomes, comparisons, or repeated analyses. In general, testing several hypotheses can increase the chance of at least one apparently unusual result, so a statistical plan may specify which outcome is primary and how secondary questions will be interpreted or adjusted. The registry lists a primary outcome of symptomatic COVID infections and a secondary outcome concerning infections, including seroconversion. The record does not report a multiplicity adjustment or a broader statistical plan. Since it reports zero analyses, there are no posted hypothesis tests whose multiplicity can be evaluated.
Missing-data methods address outcomes that were intended to be measured but are unavailable for some participants. In general, the reasons data are missing and the assumptions used to handle them can affect estimates. This record describes a different and more fundamental limitation: the trial was terminated before participants could be assigned to any arm, and it states that data were not collected or analyzed. It therefore does not report an analyzed endpoint dataset with participant-level missing outcomes. The extent or pattern of missing data is not reported in the registry record.
An analysis population defines which participants contribute to a particular result, such as everyone randomized or those who completed a specified assessment. Such definitions matter because excluding participants can change the interpretation of a comparison. The registry does not report an analysis population, and no arm assignment occurred according to its outcome description. No intention-to-treat, per-protocol, or other analysis population result is reported in the registry record.
Accordingly, neither multiplicity adjustment nor missing-data handling can be judged from the posted record. These are not merely undocumented details of a completed analysis: the registry says an analysis did not take place.
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 |
|---|---|---|---|
| CQ and Placebo Group | 0 | 5 | 0.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| CQ and Placebo Group | 0 of 5 |
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 |
|---|---|
| CQ and Placebo Group | 0 of 5 |
The registry lists serious adverse event figures under a combined group titled CQ and Placebo Group. It records 5 at risk for serious adverse events and 0 affected; for other adverse events, it records 5 at risk and 0 affected; deaths are recorded as 0. These are aggregate registry entries rather than separate CQ-versus-placebo results.
The record also states that the trial was terminated before participants could be assigned to any arm. Therefore, the safety figures cannot be interpreted as an arm-specific comparison, and they do not establish how the two planned groups would have differed. The record does not report event terms among serious adverse events.
In general, a zero recorded count means that no events appear in that particular reported category; it does not establish that an intervention has no risk. Interpretation also depends on the number exposed, observation time, completeness of reporting, and the definition of each event category. The registry does not provide a treatment-specific exposure period or a completed safety analysis. The figures should be read as limited aggregate reporting, not as evidence of comparative safety or as a substitute for the missing randomized outcome data.
12. What the Result Does, and Does Not, Mean
The result of statistical interest would have been a comparison of symptomatic COVID infections between health care workers assigned to CQ and those assigned to placebo. The registry record does not contain that result. It says the trial was terminated before participants could be assigned to any arm, with no data collected or analyzed. There is consequently no estimated effect, no measure of precision, and no inferential finding about the planned primary question.
This does not mean that the two interventions produced the same outcome. Equality cannot be concluded when no randomized outcome comparison was made. It also does not mean that CQ prevented infections or that it failed to do so. Both claims would require data that the registry says were not collected or analyzed. The same restraint applies to the secondary infection and seroconversion question.
The enrollment entry of 5 should not be mistaken for a completed treatment-group sample. The record's explicit statement about termination before arm assignment takes precedence for interpreting whether a randomized comparison occurred. Similarly, the aggregate adverse-event counts do not establish an arm-specific safety difference.
In general, a completed randomized trial can estimate an effect in the population and under the conditions studied, with uncertainty described through an appropriate interval and analysis. Even then, a result must be interpreted in light of outcome definitions, follow-up, and precision. Here, the posted record does not provide those efficacy estimates, so neither the size nor the direction of an effect can be assessed.
The defensible conclusion is that this registry record documents a planned phase 2 prophylaxis study but does not answer its clinical question. The planned design and endpoint explain what investigators intended to evaluate; they are not evidence that the intervention changed outcomes. No treatment recommendation follows from these registry results.
13. Why This Trial Matters Statistically
This trial matters statistically because it illustrates the difference between a study design and an observed result. Randomization and quadruple masking are features of the planned design. They can help reduce bias when implemented, but they do not themselves generate evidence about treatment effects. The registry states that the study ended before participants could be assigned to an arm, so there is no randomized comparison to interpret.
It also highlights why enrollment and analysis counts must be read in context. The record lists enrollment as 5 but says no participants could be assigned to any arm and no data were collected or analyzed. A number associated with enrollment is not automatically a usable analysis sample, and it does not provide an outcome denominator. Treating it as one could create a misleading impression of evidence that is not in the record.
The planned endpoint also shows how outcome definition shapes a clinical question. Symptomatic COVID infection was distinct from the secondary interest in infection defined through antibody seroconversion. Even if one outcome had been observed, it would not automatically answer the other. In this trial, neither has an analyzed result.
Finally, the record demonstrates that uncertainty is not always expressed by a wide confidence interval or a non-significant test. Sometimes there is no estimate to report because the comparison did not occur. In that situation, the correct statistical interpretation is not that the evidence is weakly positive or negative; it is that the trial's posted results do not estimate the intervention effect. Keeping that distinction clear prevents design descriptions, registry counts, and planning calculations from being mistaken for efficacy findings.
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 dominant limitation is that the study was terminated before participants could be assigned to an arm. The registry explicitly states that outcome data were not collected or analyzed. This prevents estimation of the primary contrast and leaves the central efficacy question unanswered. The registry status is terminated, and the planned follow-up timeframe of up to 3 months does not represent observed follow-up in a completed comparison.
The record lists enrollment as 5, but does not report an analyzed population or group-specific enrollment. Because arm assignment did not occur, the entry cannot be used to infer the number exposed to CQ or placebo, or the number contributing endpoint information. The record does not report participant flow, reasons for termination, or whether any screening or preparatory activities took place.
Statistical analysis details are also limited. The record lists zero analyses and does not report an analysis plan, an effect estimate, a confidence interval, a p-value, or a method for handling missing outcomes. The registry does not report how multiple outcomes would be handled analytically or define an analysis population. These details are not reported in the registry record.
The endpoint definition includes symptoms and confirmatory anti-COVID antibodies, with PCR when available. The record does not report how often PCR would be available or how outcome disagreements would be resolved. Because no outcome data were analyzed, the consistency and completeness of endpoint ascertainment cannot be assessed.
Finally, safety figures are aggregate and do not separate the planned intervention arms. They cannot support a randomized safety comparison. Together, these limitations mean the registry supports a description of the intended study and its termination, but not an estimate of efficacy or comparative safety.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Saved From COVID-19 - Chloroquine (CQ) Prophylaxis for Health Care Workers at Risk for COVID — NCT04349371.
- Registry record last updated 2025-02-27; status last verified 2025-02.
- Results first posted 2024-08-13.
- 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.
Continue through the Clinical Biostats statistical pathway
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18. Record Summary
The registry identifies NCT04349371 as a phase 2, randomized, quadruple-masked, parallel-group study sponsored by Columbia University. It planned to compare chloroquine prophylaxis with placebo among health care workers at risk of COVID-19, with symptomatic COVID infection as the primary outcome over up to 3 months. The recorded start date is 2020-04-21, and the primary completion date is 2021-02-11.
The record lists enrollment as 5 and status as terminated. It states that termination occurred before participants could be assigned to any arm and that data were not collected or analyzed. Although two outcome measures are listed, the record reports zero analyses and no primary efficacy result. Aggregate adverse-event entries list 0 serious adverse events, 0 other adverse events, and 0 deaths, but do not provide an arm-specific comparison. The posted record therefore describes a planned trial without an analyzed treatment-effect estimate.