VISTA: Vaccinator-Initiated Screening and TAilored Counseling for Reducing Vaccine Hesitancy: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for VISTA: Vaccinator-Initiated Screening and TAilored Counseling for Reducing Vaccine Hesitancy (NCT04421586), a non-randomized na study. The primary outcome is Percentage of Women With Reduced Number of Concerns Immediately Post-counseling in the Intervention Arm.

2. Clinical Question

The broader study aim was to understand parents’ vaccine concerns and explore whether information about vaccination during pregnancy from a health provider might improve the possibility that a child is vaccinated on time. The registry lists child vaccination timing among the secondary outcomes, alongside women’s concerns at follow-up and measures of the counseling process.

These aims involve distinct questions. An immediate change in a woman’s reported concerns is a proximal measure of response to counseling. Whether children later receive vaccines within a specified window is a separate outcome involving follow-up and events after counseling. The registry record does not report the results for either question. It therefore does not establish how often concerns were reduced, whether vaccination timing differed, or how precisely any such result was estimated.

3. Trial Design

The registry describes VISTA as a completed, parallel, non-randomized study with no masking. The recorded enrollment is 60. The arm descriptions state that up to 30 pregnant women were to receive VISTA screening and counseling for vaccine concerns, and up to 30 pregnant women were to receive usual care. These are the arm descriptions, not evidence that each arm enrolled exactly the maximum number.

Because assignment was non-randomized, differences between the arms may reflect differences in who entered or was assigned to each group as well as any effect associated with counseling. Random allocation is commonly used to balance measured and unmeasured characteristics on average; that protection is not described for this study. The record does not report how allocation decisions were made, what characteristics were used, or whether any adjustment was planned. The arms therefore should not be interpreted as a randomized, like-for-like control comparison.

The intervention is classified as behavioral. The study’s brief description frames the counseling as information about vaccinations during pregnancy, while the arm description specifies screening and counseling for vaccine concerns. The listed outcomes include both participant-reported responses and process measures, such as counseling checklist completion and minutes spent delivering counseling. They also include child vaccination timing and days children remained unvaccinated for each vaccine.

The registry identifies the phase as NA, names Duke University as sponsor, and records the study start as 2020-09-02, primary completion as 2021-05-24, and status as completed. Completion status indicates the recorded status of the study, not that every planned outcome has a posted result. The registry record does not report the recruitment setting, eligibility criteria in detail, allocation procedure, or follow-up schedule beyond the time descriptions attached to the outcomes.

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

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Outcome measure only applies to the VISTA arm.

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: Participants on whom baseline/demographic data was collected.

6. Primary Endpoint

The registry lists the primary outcome as Percentage of Women With Reduced Number of Concerns Immediately Post-counseling in the Intervention Arm, measured over Post-counseling (Baseline visit).

The primary endpoint is the percentage of women with a reduced number of concerns immediately after counseling in the VISTA intervention arm. Its stated timeframe is post-counseling at the baseline visit, and the registry explicitly says that this outcome applies only to the VISTA arm. It is therefore a within-arm outcome, not a direct estimate of the difference between VISTA and usual care.

As a measure, the endpoint is intended to capture whether the number of concerns is lower after the counseling encounter than at the relevant earlier assessment. In general, an immediate response measure can describe a short-term change close to the intervention, while saying less about whether the change persists or alters later behavior. Here, the endpoint title identifies a reduced number of concerns, but the registry record does not report the operational definition of a concern, the measurement instrument, the threshold for classifying a woman as having a reduction, or how missing responses were handled.

The endpoint is relevant to the stated counseling aim because it concerns participants’ vaccine concerns. It does not itself measure child vaccination, vaccine timeliness, or the comparative effect of VISTA versus usual care. The percentage and its uncertainty are not reported in the registry record. Consequently, the record does not establish how many women met the endpoint or how precisely that percentage was estimated.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does the primary endpoint estimate?

The endpoint is a percentage within the intervention arm: women classified as having a reduced number of concerns after counseling, relative to the relevant earlier assessment. A percentage is a proportion expressed on a scale from no participants meeting the definition to all participants meeting it. The registry record does not state the observed percentage, its denominator, or the exact rules used to classify a reduction. It also does not report a confidence interval. No numerical estimate should therefore be inferred from the study description or from the enrollment and arm-planning figures.

Why does an interval matter?

General statistical explanation: an estimate from a sample is subject to sampling variation. A confidence interval conveys a range of values compatible with the data and the interval’s statistical procedure, under its assumptions. A narrow interval indicates greater precision than a wide interval, but neither an interval nor a point estimate alone resolves bias from non-randomized allocation or measurement choices. The registry record does not report an interval for the primary endpoint.

What does non-randomized allocation change?

General statistical explanation: in a randomized study, allocation by chance is intended to make groups comparable on average, including on characteristics that may not have been measured. In a non-randomized study, assignment may be associated with participant characteristics or other factors related to the outcome. A crude comparison can then combine intervention-associated differences with pre-existing differences. Adjustment for measured characteristics can sometimes address some imbalance, but cannot automatically remove unmeasured confounding and depends on the chosen variables and model. The allocation process and any adjusted analysis are not reported in the registry record, so the degree to which these issues were addressed is unknown.

What analyses are reported?

The record lists 0 analyses. It does not report a statistical model, the handling of repeated measurements, a definition of the analysis population, or a plan for missing observations. It also does not report a test statistic, p-value, or confidence interval for the primary endpoint or the listed secondary outcomes. These absences prevent a reconstruction of the sponsor’s analysis from the registry information.

The outcome list includes percentages, a median number of days, checklist completion, counseling duration, and participant responses about helpfulness, reduced concerns, and understanding. These outcomes have different scales and meanings, so a single common effect measure would not capture them all. For example, a percentage summarizes a proportion, while a median summarizes the middle of a distribution of durations. The registry record does not report how any of these outcomes were summarized or compared.

Why can over-dispersion matter?

General statistical explanation: count outcomes are sometimes analyzed using a model that assumes a particular relationship between the average count and its variability. If the observed variability is larger than that assumed by the model, over-dispersion may make standard errors too small and confidence intervals too narrow unless the analysis accounts for it. The primary outcome is described as a percentage, and the record does not identify a count model or an over-dispersion assessment. This is a general consideration, not a claim that over-dispersion occurred in VISTA.

How should the planning illustrations be read?

The sample-size illustrations are planning scenarios based on the observed effect, rather than the trial’s own design justification. Their stated assumptions are a two-sided significance level of 0.05, equal allocation between arms, and a normal approximation; the effect to detect is expressed as a stated share of the observed effect. For time-to-event illustrations, the stated quantity is the total number of events; for other illustrations, it is participants per arm. These scenarios describe hypothetical planning requirements under assumptions. They are not observed power, do not establish the precision of the completed study, and do not replace the missing outcome estimates. The registry record does not report the original design justification or sample-size rationale.

General statistical explanation: power is a design quantity concerning the probability that a specified analysis detects a specified effect under stated assumptions. Calculating a hypothetical sample size from an observed effect after data collection is not evidence that the completed study had a particular level of power. Such a calculation also depends on the effect chosen for planning and on the assumptions used. No numerical sample-size scenario is restated because the registry information does not give those scenario values.

What does the outcome list imply for interpretation?

The outcomes include a participant-reported immediate response, follow-up concerns, child vaccination timing, time unvaccinated, and counseling implementation. General statistical explanation: these outcomes can address different questions and may have different sources of uncertainty. A measure of counseling delivery does not by itself show a change in child vaccination, and a vaccination-timing measure does not identify why an outcome occurred. Interpreting each outcome requires its own definition, analysis, and uncertainty estimate. Those detailed results and methods are not reported in the registry record.

10. Multiplicity, Missing Data and Analysis Populations

The registry record lists 16 outcome measures, including a primary endpoint and multiple secondary outcomes. The listed secondary measures cover concern reduction at follow-up, child vaccination timing, days children remain unvaccinated, completion of counseling checklist items, counseling duration, and participants’ views of the community health worker’s information. These outcomes address different questions, but examining many outcomes can create a multiplicity concern if each is tested and interpreted as confirmatory.

General statistical explanation: when many statistical tests are conducted, the chance of at least one apparently unusual result can increase if the tests are treated independently and no adjustment or prioritization is used. Analysts may address this by prespecifying a hierarchy, adjusting for multiple tests, or treating secondary findings as exploratory. The registry record does not report a multiplicity strategy, outcome hierarchy beyond identifying the primary endpoint, or a statistical analysis plan. It also lists 0 analyses, so no test results are available for evaluating how multiplicity was handled.

Missing-data methods are not reported in the registry record. The record does not state whether outcome data were missing, how missing responses or follow-up assessments were handled, or whether any sensitivity analysis was conducted. This matters in general because complete-case results can be biased if the likelihood of missingness is related to participant characteristics or outcomes.

The analysis populations are also not described. The registry record does not report whether analyses were intended to include all enrolled participants, only participants who received counseling, or another defined group. No denominators for the primary outcome are reported. As a result, neither the extent of missingness nor the relationship between the population enrolled and the population analyzed can be assessed.

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 30 women at risk for serious adverse events in the VISTA counseling arm and 0 affected; it lists 30 at risk and 0 affected in the usual-care arm. For other adverse events, it likewise lists 30 at risk and 0 affected in each arm. Deaths are listed separately: 0 in the VISTA arm and 1 in the usual-care arm.

These are descriptive registry counts. The record does not provide event descriptions, timing, severity details beyond the serious-event category, or information establishing whether a death or any event was related to study participation. The separate death count should not be interpreted as proof of a causal effect of usual care or as evidence about counseling. Non-randomized allocation further limits causal comparisons between the arms.

Zero affected participants in a category does not establish that the true risk is zero. General statistical explanation: when events are uncommon, a study may observe none even though the underlying event probability is not zero; the precision of a safety estimate depends on the amount and completeness of follow-up as well as the number of events. The registry record does not report an uncertainty interval or additional follow-up detail for these counts. These figures should therefore be read as the events recorded in the registry, not as a definitive comparison of safety.

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

The record documents a study of VISTA counseling for pregnant women with vaccine concerns and a usual-care arm. It identifies an immediate post-counseling primary outcome concerning reduced concerns, and secondary outcomes spanning later concerns, child vaccination timing, time unvaccinated, and counseling delivery. This provides a clear outline of the questions the study was intended to explore.

It does not report the numerical primary endpoint result. The percentage of women whose number of concerns was reduced, the number of women contributing to that estimate, and its uncertainty are not reported in the registry record. Nor are numerical results reported for the listed secondary outcomes. Thus, the record does not show whether concerns changed, whether children received vaccines within the stated window, or how counseling was delivered in practice.

The primary endpoint is limited to the VISTA arm, so it does not by itself estimate a difference from usual care. The study’s non-randomized allocation also means that any future arm contrast would need careful interpretation: group differences may arise from factors other than the intervention. The registry record does not report an allocation procedure or adjusted analysis that would clarify how this issue was handled.

The completion status and recorded enrollment do not fill these gaps. A completed study can have outcome results that are not reported in a registry record, and a planned arm size is not an observed endpoint denominator. Similarly, sample-size planning illustrations are not evidence of the trial’s observed precision or power. The adverse-event counts are useful descriptive entries, but they do not establish causation or settle comparative safety.

Accordingly, the registry record describes the design and intended measures but does not support a conclusion about the magnitude of a counseling-associated change or a comparative effect on child vaccination. The absence of reported results should not be interpreted as evidence that the intervention had no effect, nor as evidence that it did. It means the posted registry information is insufficient to determine the results.

13. Why This Trial Matters Statistically

VISTA raises a statistical distinction between a proximal response and a later behavioral outcome. A reduction in concerns immediately after counseling concerns participants’ responses at the encounter, while vaccination timing concerns what happens later for children. Those outcomes can be related, but one cannot stand in for the other. A clear interpretation depends on keeping the endpoint’s timing and meaning in view.

The primary outcome is an intervention-arm percentage rather than a direct comparison with usual care. This makes the distinction between describing a group and estimating an intervention contrast especially important. A within-arm change can be informative about what was observed among participants receiving counseling, but without a suitable comparator it cannot isolate what would have happened without that counseling.

The non-randomized design further illustrates the role of allocation in inference. Even when a study includes a usual-care group, a comparison is not automatically equivalent to a randomized comparison. Differences in group composition or circumstances may complicate interpretation, and readers need to know whether the analysis addressed these issues. The registry record does not report those details.

The breadth of the outcome list also matters statistically. Measures of concerns, vaccination timing, duration without vaccination, and counseling process each capture a different part of the study’s aims. Their results would need to be interpreted individually, with suitable uncertainty estimates and attention to the number of outcomes examined. The record lists 16 outcome measures but does not report analyses or results.

Finally, this record demonstrates why a completed status is not the same as a complete statistical account. Without numerical outcome estimates, denominators, uncertainty, and analysis details, readers cannot assess the size, precision, or robustness of the findings. The design and outcome definitions are informative, but reported results are necessary to evaluate what was observed.

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.

Several trial-specific details needed to interpret the results are not reported in the registry record. The allocation process is not described, despite the non-randomized design. There is no account of how women entered either arm, whether group assignment depended on clinical or participant characteristics, or whether analyses adjusted for such differences. This limits interpretation of any comparison between VISTA and usual care.

The primary endpoint is restricted to the VISTA arm, and the registry record does not give its observed percentage or denominator. The measurement instrument, the definition of a concern, and the rule for classifying a reduction are not reported. Without these details, readers cannot determine how the outcome was operationalized or reproduce its classification.

Although several outcomes concern follow-up and children’s vaccination, the record does not report follow-up completeness, outcome-specific denominators, or the handling of missing observations. The precise timing and assessment procedures beyond the stated outcome timeframes are not reported. These omissions limit assessment of whether the planned outcomes were measured consistently and whether attrition could affect interpretation.

The registry lists 16 outcome measures and 0 analyses but does not report the statistical analysis plan, multiplicity approach, analysis populations, or adjusted estimates. This prevents assessment of whether the outcomes were prioritized as planned, whether comparisons accounted for the design, and how uncertainty was quantified. The recorded enrollment and arm descriptions do not establish the number of participants contributing to each outcome.

Finally, the study is marked completed, yet numerical results for the primary and secondary outcomes are not reported in the registry record. The listed adverse-event counts also lack event descriptions and causal assessments. These limitations concern the available registry information; they do not establish what results may exist outside that record.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: VISTA: Vaccinator-Initiated Screening and TAilored Counseling for Reducing Vaccine Hesitancy — NCT04421586.
• Registry record last updated 2024-01-05; status last verified 2023-03.
• Results first posted 2024-01-05.
• 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

VISTA is a completed, parallel, non-randomized behavioral study sponsored by Duke University. It examines screening and tailored counseling for vaccine concerns among pregnant women, with usual care as the comparator arm. The recorded enrollment is 60, and each arm description specifies up to 30 women. The study has no masking.

The primary endpoint is the percentage of women in the VISTA arm with a reduced number of concerns immediately after counseling. Secondary outcomes include follow-up concerns, child vaccination timing, days unvaccinated, counseling checklist completion and duration, and participants’ views of the information. The record lists 16 outcome measures and 0 analyses.

The registry record does not report numerical results for the primary or secondary outcomes, confidence intervals, or the statistical analysis plan. It lists 0 serious adverse events and 0 other adverse events affected in each arm, and deaths of 0 in the VISTA arm and 1 in usual care. These counts are descriptive and do not establish causation or comparative safety.