COVID-19: Povidone-Iodine Intranasal Prophylaxis in Front-line Healthcare Personnel and Inpatients: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for COVID-19: Povidone-Iodine Intranasal Prophylaxis in Front-line Healthcare Personnel and Inpatients (NCT04364802), a non-randomized phase 2 study. The primary outcome is Percent of Healthcare Workers Testing Positive for COVID-19..

2. Clinical Question

The study asks whether adding povidone-iodine (PVP-I) nasal spray and gargle to the care or protections described for participants is associated with fewer positive COVID-19 tests during the study. The primary endpoint focuses on healthcare workers; inpatient and community participants are also included in the study arms, but they are not part of that primary endpoint.

The comparison is non-randomized, and the registry record cautions that the arms are not a like-for-like control comparison. Consequently, the study question is best understood as an evaluation across separate participant groups and treatment assignments, not as a randomized comparison designed to isolate the effect of PVP-I. The registry record does not report a primary endpoint estimate, a confidence interval or a statistical test.

3. Trial Design

This is a completed phase 2, parallel, non-randomized study with no masking. The registry record lists an enrollment of 98 and describes six arms: control and PVP-I groups among healthcare workers, inpatients and community participants. The study began on 2020-04-29, and its primary completion date is 2022-01-28.

The groups have different eligibility descriptions and background care. Front-line healthcare workers are COVID-19-negative and receive standard PPE, with pre- and post-study COVID-19 testing. The PVP-I healthcare worker group receives the same described protections and testing, as well as PVP-I spray and gargle. Inpatients are eligible if they have a 7+ day hospitalization or are set to undergo a significant surgical procedure. Their control group receives standard care and pre- and post-study testing; the PVP-I group receives the same described care and testing, with PVP-I sprays applied shortly after admission or perioperatively. Community participants are COVID-19-negative and receive pre- and post-study testing, with PVP-I spray and gargle added in the intervention group.

Because assignment is non-randomized, differences between the groups could reflect participant characteristics, setting, care, exposure or other factors, as well as any difference associated with the intervention. The registry record itself notes that the arms are not a like-for-like control comparison. The parallel structure means groups are followed in the same general study period rather than participants being described as switching between conditions; further details of the study schedule are not reported in the registry record. The phase designation and completed status describe the registered study, but do not establish that the primary question was answered or that results were statistically conclusive.

The registry record does not report the method used to assign participants, the intended PVP-I dose or frequency, or a fuller protocol for adherence and follow-up. These details should not be inferred from the brief arm descriptions.

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.

Overall Study

Analysis population for the primary outcome, as defined in the registry: This outcome measure pertains only to the arms that include healthcare workers.

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.

Only the first 6 of 7 groups are shown.

6. Primary Endpoint

The registry lists the primary outcome as Percent of Healthcare Workers Testing Positive for COVID-19., measured over 3 weeks.

The primary endpoint is the percentage of healthcare workers who become positive for COVID-19 during the study. Its stated timeframe is 3 weeks. The endpoint applies only to the healthcare worker arms, rather than to all participants enrolled across the inpatient and community groups.

A percentage describes how often an event occurs in a defined group, making it a direct way to express the proportion of healthcare workers who test positive over the specified period. For this question, the event is a positive COVID-19 test during the study. The registry record describes pre- and post-study testing for healthcare workers and defines the primary outcome as becoming positive during the study. More detailed rules for classifying a positive result, handling tests at different times, or resolving missing test results are not reported in the registry record.

The outcome is relevant to the stated prophylaxis question because it concerns infection detected over the follow-up period. However, the endpoint definition alone does not show how many participants tested positive in either healthcare worker group, or whether the groups differed. Those results, together with an estimate of uncertainty and the statistical analysis used, are not reported in the registry record. The listed adverse-event counts are a separate type of information and should not be treated as the primary infection outcome.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

Interpreting a clinical comparison requires more than knowing the intervention and outcome. Readers need to know how participants entered each group, how outcomes were measured, which participants were included in each analysis, and how estimates and uncertainty were calculated. The registry record identifies the study as non-randomized, unmasked and parallel. It does not report statistical analyses, and it does not give a detailed analysis plan.

What does non-randomized allocation mean?

In a randomized study, a chance-based assignment process is intended to reduce systematic differences between groups. In a non-randomized study, group assignment does not have that protection. For example, setting, health status, exposure circumstances or decisions about care could differ across groups and also relate to the chance of a positive test. Such factors can confound a comparison: an apparent difference between groups may reflect those factors, the intervention, or both. This is a general statistical concern, not a claim that any particular imbalance occurred in this study.

The registry record warns that the arms are not a like-for-like control comparison. That warning matters when interpreting any contrast, even if a numerical result is later reported. Statistical adjustment can sometimes account for measured differences, but it cannot automatically remove confounding from factors that were not measured or modeled. The registry record does not describe adjustment variables or an adjusted analysis.

How should a percentage outcome be understood?

The primary measure is a percentage of healthcare workers who become positive during the stated 3 weeks. In general, a percentage is a summary of the event frequency within a defined group. To interpret it, readers need the event count and the number of participants contributing outcome data in each group. The registry record defines the endpoint but does not report those counts or percentages. It also does not state how participants with incomplete testing or follow-up were handled.

A comparison of percentages can be expressed in different ways, such as a difference in proportions or a relative measure. Choosing a measure should be guided by the clinical question and analysis plan. No primary effect estimate is reported in the registry record, so no such comparison can be described for this study. Recalculations from summary statistics are not possible from the recorded primary outcome information.

What would a confidence interval add?

In general, a confidence interval expresses the uncertainty around an estimated effect under the assumptions of the statistical method. A narrow interval indicates greater precision than a wide interval, while the interval's location indicates which effect values are compatible with the data and method. It does not account for every source of bias, particularly bias from non-randomized assignment or incomplete outcome ascertainment. No confidence interval for the primary outcome is reported in the registry record.

A p-value, when reported, measures how unusual the data would be under a specified null model and its assumptions. It does not measure the probability that the null hypothesis is true, and it does not establish that a finding is clinically important. The registry record does not report a primary p-value or statistical test. No statistical analysis results are listed.

What is known about sample-size planning?

The registry record describes a planning illustration based on an observed effect, with 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 an illustration, not evidence that the study had a particular level of power. Sample-size illustrations are planning quantities, not observed power, and should not be read as proof that the design was adequately sized.

The registry record does not report the trial's own sample-size justification or protocol rationale. It also does not provide the primary outcome result needed to evaluate an observed effect in context. The stated illustration assumptions therefore cannot establish what effect the study was designed to detect under its actual enrollment and allocation.

Why do setting and follow-up matter?

The three participant settings differ in eligibility and background care. Healthcare workers receive standard PPE, inpatients receive standard care, and community participants have testing described without the same background-care description. These differences can affect both exposure and outcome measurement. The primary endpoint is limited to healthcare workers, so outcomes from the inpatient and community groups do not directly answer that endpoint.

In general, an outcome observed over a fixed follow-up period depends on consistent testing and adequate follow-up. The registry record describes pre- and post-study COVID-19 testing for healthcare workers and inpatients, but it does not report the detailed testing schedule or rules for missing tests. It does not describe how adherence to PVP-I use was assessed. Without these details, readers cannot determine how fully the endpoint was ascertained or how closely intervention use matched the intended regimen.

10. Multiplicity, Missing Data and Analysis Populations

The registry record lists six outcome measures and names PVP-I ease of use and comfort among the secondary outcomes. It does not report a statistical analysis plan describing which outcomes were confirmatory, how many comparisons were planned, or whether any adjustment for multiple testing was intended. When several outcomes or comparisons are examined, the chance of at least one apparently notable result can increase. In general, multiplicity methods help control that risk, but their relevance depends on the prespecified analysis strategy. No such strategy is reported in the registry record.

Missing outcome data are also important for interpreting a percentage of participants who test positive. If some participants lack follow-up tests, the result may depend on how those participants are treated in the analysis. The registry record does not report the amount or pattern of missing primary endpoint data, the number analyzed in each group, or any method for handling missing tests. It does not report an intention-to-treat population, a per-protocol population, or another defined analysis population for the primary endpoint.

These omissions do not establish that data were missing or that analyses were conducted in a particular way. They mean those details are not reported in the registry record. Without an analysis population and missing-data account, readers cannot assess whether the reported enrollment corresponds to the participants included in the outcome analysis, and no primary outcome result is available to evaluate.

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.

The registry record lists serious adverse events, other adverse events and deaths for each of the six groups. For Healthcare Workers - Control, 0 of 11 participants at risk are listed as affected by a serious event, 0 of 11 by another event, and deaths are 0. For Healthcare Workers - PVP-I, the corresponding counts are 0 of 38, 0 of 38 and 0 deaths.

For Inpatients - Control, the listed counts are 0 of 17 for serious events, 0 of 17 for other events and 0 deaths. For Inpatients - PVP-I, they are 0 of 14, 0 of 14 and 0 deaths. For Community - Control, they are 0 of 2, 0 of 2 and 0 deaths. For Community - PVP-I, they are 0 of 16, 0 of 16 and 0 deaths.

These are registry-listed event counts, not an estimate of the primary COVID-19 outcome. A zero count means no affected participants are recorded in that category for the group; it does not, by itself, establish complete safety follow-up or exclude unrecorded events. The registry record does not report additional detail about event collection, follow-up completeness or how events were classified beyond the serious and other categories.

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

The registry record supports a description of what the study set out to evaluate: PVP-I nasal spray and gargle as prophylaxis in healthcare workers, inpatients and community participants, with the primary endpoint focused on healthcare workers testing positive during 3 weeks. It also establishes that the study was completed, was non-randomized and had an enrollment of 98.

It does not report the primary outcome results. No group-specific number of positive tests, percentage, effect estimate, confidence interval or p-value is included in the record described. The size, direction and precision of any difference between healthcare worker groups therefore cannot be assessed. The recorded absence of adverse events in the safety categories is not a substitute for the infection endpoint, and cannot answer whether the primary outcome differed.

Even if a numerical outcome contrast were available, the non-randomized design would require careful interpretation. The registry record notes that the arms are not a like-for-like control comparison. Differences in participant characteristics, exposure, setting or other factors could contribute to a contrast. The record does not describe statistical adjustment that would address these possibilities.

The lack of posted efficacy results should not be interpreted as evidence of no effect, nor as evidence of benefit. It indicates that the registry record does not provide the information required to estimate or assess the primary outcome. Likewise, the completed status indicates the study's registered status, not that the primary question has a reported statistical answer.

Thus, the study record is informative about the planned populations, intervention, comparator conditions and endpoint definition, while leaving the main efficacy question unresolved in the posted results. Any conclusion about the primary endpoint would require outcome data and analysis details that are not reported in the registry record.

13. Why This Trial Matters Statistically

This study raises statistical issues that are common in clinical research conducted across different care settings. Its parallel groups include healthcare workers, inpatients and community participants, but the primary endpoint concerns healthcare workers alone. Keeping the endpoint population distinct from the overall enrollment is essential: a total enrollment figure cannot tell readers how many healthcare workers had outcome data or how many tested positive.

The non-randomized design is another important point. Comparisons without random assignment can be difficult to interpret because group differences may be related to factors other than the intervention. The registry's warning that the arms are not a like-for-like control comparison makes the design limitation explicit. This is a reason to distinguish description of the groups from causal interpretation of a treatment contrast.

The record also illustrates why a defined endpoint and a completed study status are not enough to evaluate results. A percentage outcome requires event counts and denominators, while assessment of uncertainty requires an estimate and an appropriate analysis. Those primary outcome results are not reported. The safety counts are available, but they answer a different question and should not be conflated with infection results.

Finally, the record identifies secondary outcomes related to ease of use and comfort, yet does not report statistical analysis details or how multiple outcomes were handled. This leaves readers unable to assess the analysis strategy and its relation to the outcome list. Statistically, the record is useful for understanding the intended comparison and its limitations, but it cannot support a quantitative conclusion about the primary efficacy question.

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 main limitation for interpreting the registered results is that no primary endpoint data or statistical analysis results are reported in the registry record. The endpoint is defined, but group-specific positive-test counts, percentages, effect estimates and uncertainty measures are absent. As a result, the primary outcome cannot be evaluated quantitatively.

The study is non-randomized, and the record warns that the arms are not a like-for-like control comparison. This limits causal interpretation because factors associated with group assignment may also relate to infection risk. The record does not describe an adjustment strategy or the variables that might have been measured for that purpose.

The participant groups also differ by setting and eligibility. The healthcare worker endpoint cannot be directly extended to inpatients or community participants. The record does not report detailed information on participant flow, group-specific numbers analyzed, adherence to PVP-I, or completeness of follow-up testing. The stated pre- and post-study testing descriptions do not specify all operational details for outcome ascertainment.

The registry lists six outcome measures but does not report a detailed statistical analysis plan, handling of multiple comparisons, missing-data procedures or defined analysis populations. The sample-size information is described as a planning illustration rather than the study's own design justification; the registry record does not report that justification. These gaps leave uncertainty about how analyses were intended and whether the posted safety summaries represent complete follow-up. They do not prove that any particular problem occurred, but restrict what can be concluded from the record.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: COVID-19: Povidone-Iodine Intranasal Prophylaxis in Front-line Healthcare Personnel and Inpatients — NCT04364802.
• Registry record last updated 2022-12-02; status last verified 2022-11.
• Results first posted 2022-12-02.
• 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

NCT04364802 is a completed phase 2, parallel, non-randomized, unmasked study of PVP-I nasal spray and gargle for COVID-19 prophylaxis. The registry record lists an enrollment of 98 and six arms covering healthcare workers, inpatients and community participants. It began on 2020-04-29, with primary completion on 2022-01-28.

The primary endpoint is the percentage of healthcare workers testing positive for COVID-19 during 3 weeks. The registry record does not report primary endpoint results or statistical analyses. It lists zero serious events, zero other adverse events and zero deaths in each group. The record cautions that the groups are not a like-for-like control comparison.