Protecting Against HIV Vaccine Misinformation With Adolescent Girls and Young Women in South Africa: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Protecting Against HIV Vaccine Misinformation With Adolescent Girls and Young Women in South Africa (NCT06700447), a randomized na study. The primary outcome is HIV Vaccine Intention, at the End of the Baseline Assessment.

2. Clinical Question

The registry describes the primary objective as comparing changes in intention following misinformation exposure between groups with and without psychological inoculation and a behavioral-economics boost. The primary result posted for this comparison is a difference in mean scores. The outcome is an intention measure, not a measure of actual vaccination or HIV infection.

The record also lists questions about vaccine intention at follow-up, recommendations to friends, and the credibility of misinformation exposures. These secondary outcomes can add context about responses to the messages, but they do not change what the primary endpoint measures. Subgroup effects are mentioned among the study objectives; subgroup results are not reported in the registry record.

3. Trial Design

The record describes a randomized, double-masked, parallel study sponsored by the University of Pennsylvania. Its phase is listed as NA, and its enrollment is 2163. The registry status is active, not recruiting. The listed study start is 2025-07-24, and the listed primary completion is 2025-10-16.

The comparison of interest is between the Enhanced Inoculation Message arm and the Control arm. The enhanced message is intended to warn participants about HIV-vaccine misinformation and explain why claims are false or misleading, with behavioral-economics insights. The Control arm receives unrelated diabetes and nutrition information and is described as an attention control. The posted primary results include 1083 participants in the enhanced-message arm and 1080 in the Control arm.

The primary outcome is continuous: intention to get an HIV vaccine on a 1-10 scale, with higher scores indicating greater intention. It is measured after the inoculation intervention and misinformation exposure, at the end of the baseline assessment. Follow-up outcomes are listed at 2-4 weeks. For the follow-up vaccine-intention result, the posted arm sample sizes are 969 and 967, respectively.

The registry record does not report the original sample-size justification, the planned statistical analysis, allocation details beyond randomized assignment, or the procedures used to implement masking. The record also contains no reported analyses. The numerical comparisons discussed in the posted results are simple, unadjusted recalculations from arm-level summary statistics rather than a reported sponsor analysis.

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

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.

6. Primary Endpoint

The registry lists the primary outcome as HIV Vaccine Intention, at the End of the Baseline Assessment, measured over At the end of the baseline assessment.

The primary endpoint is mean intention to get an HIV vaccine, measured on a 1-10 scale after the inoculation intervention and misinformation exposure. The registry specifies that higher scores mean greater likelihood of intending to get the vaccine. The measurement occurs at the end of the baseline assessment, despite the outcome's timing after the intervention and exposure.

Intention is used to capture a participant's stated response to the possibility of receiving an HIV vaccine. In a study about misinformation messages, this outcome can describe whether responses differ between the enhanced inoculation message and an attention-control message. It is not a direct measure of behavior: a stated intention does not establish whether someone would later receive a vaccine. Nor does this endpoint measure HIV infection, vaccine effectiveness, or the safety of a vaccine.

The primary posted summaries report mean scores and standard deviations for each group, together with an unadjusted mean difference and its confidence interval. The registry record does not report the planned model, any covariate adjustment, or a sponsor analysis for this endpoint. Interpretation therefore centers on the posted arm summaries and the simple unadjusted comparison, with the limits that follow from the absence of a reported analysis plan.

7. Results Posted in the Registry

• Enhanced Inoculation Message: mean 7.77 versus 7.81 on control; difference -0.04 (95% CI -0.28 to 0.20), standardized effect d = -0.01; z-test p = 0.744.

8. Secondary Efficacy Endpoints

The registry also posts results for secondary outcomes. For each outcome below, the endpoint type, the test applied to the posted summary statistics, the result and its interpretation are given in turn. Secondary endpoints are usually not adjusted for multiple testing, so they support rather than confirm the primary finding.

HIV Vaccine Intention, Follow-up

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Enhanced Inoculation Message: mean 7.82 versus 6.82 on control; difference 1.00 (95% CI 0.75 to 1.25), standardized effect d = 0.36; z-test p = <0.001.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the mean is statistically higher for Enhanced Inoculation Message than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

Recommend to Friends, at the End of the Baseline Assessment

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Enhanced Inoculation Message: mean 8.55 versus 8.53 on control; difference 0.02 (95% CI -0.17 to 0.21), standardized effect d = 0.01; z-test p = 0.839.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Enhanced Inoculation Message and the control. The interval gives the range of effects that remain compatible with the data.

Recommend to Friends, Follow-up

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Enhanced Inoculation Message: mean 8.12 versus 7.21 on control; difference 0.91 (95% CI 0.67 to 1.15), standardized effect d = 0.34; z-test p = <0.001.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the mean is statistically higher for Enhanced Inoculation Message than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

The secondary results show a mixed pattern across timing and outcome. The follow-up vaccine-intention and recommendation-to-friends summaries favor the enhanced-message group, while recommendation-to-friends means at the end of the baseline assessment are very similar. The registry also lists credibility ratings for misinformation exposures and other secondary measures. Taken together, the posted results suggest that the pattern is not uniform across all listed outcomes or time points.

The primary comparison is the intention measure at the end of the baseline assessment, where the group means are close and the unadjusted interval includes zero. Follow-up differences are relevant context, but they answer a different timing question and should not be substituted for the primary result. Nor do the secondary outcomes establish a change in actual vaccine behavior.

The registry record lists 48 secondary outcomes and no reported analyses. The posted secondary comparisons are unadjusted. When many outcomes are considered, the chance of seeing apparently strong results by chance increases unless the analysis accounts for multiplicity or gives outcomes an appropriate prespecified hierarchy. The registry record does not report a multiplicity adjustment, a hierarchy for the secondary outcomes, or which comparisons were planned in advance.

For these reasons, secondary results are best treated as exploratory signals that may help motivate further evaluation, not as confirmatory evidence on their own. Their relationship to the primary result depends on outcome timing, the measure used, missing data, and the statistical plan, details that are not fully reported in the registry record. The presence of a small unadjusted p-value for a secondary endpoint does not alter the interpretation of the primary endpoint or establish that the broader intervention has a consistent effect.

Secondary outcomes registered for this trial, for reference (only those above were recalculated):

• HIV Vaccine Intention, Follow-up
• Recommend to Friends, at the End of the Baseline Assessment
• Recommend to Friends, Follow-up
• Credibility of Inoculated Exposure #1
• Credibility of Inoculated Exposure #2
• Credibility of Inoculated Exposure #3
• Credibility of Inoculated Exposure #4
• Credibility of Inoculated Exposure #5

9. Statistical Interpretation

10. Statistical Methods Explained

What does the mean difference describe?

For a continuous outcome, a mean difference compares the average score in one group with the average score in the comparison group. The posted primary estimate is -0.04 for Enhanced Inoculation Message relative to Control. Its negative sign indicates that the enhanced-message group mean is lower in this comparison. The estimate is unadjusted and is based on the posted group summaries; it is not a covariate-adjusted treatment estimate reported by the sponsor.

The arm means and standard deviations provide useful context for that comparison. The primary means are 7.81 and 7.77, and the standard deviations are 2.87 and 2.82. A standard deviation describes how dispersed individual scores are around a group mean. It is not a confidence interval for the mean and does not describe the uncertainty in the difference by itself.

What does the confidence interval add?

A confidence interval gives a range of values compatible with the observed data under the method used to calculate it. It conveys uncertainty about the estimated group difference. For the primary comparison, the interval includes zero, so the posted data are compatible with no mean difference as well as with differences in either direction. This is not evidence that the true difference must be zero. The registry record does not report a sponsor analysis or a planned model, so the interval should be understood as part of the simple unadjusted recalculation from summary statistics.

How should the p-value be read?

The primary unadjusted p-value is 0.744. A p-value describes how unusual data at least as discrepant as those observed would be under a specified null model and its assumptions. It is not the probability that the null hypothesis is true, and it does not measure the size or practical importance of a difference. The p-value is consistent with the small estimated primary difference and the interval that includes zero. It does not prove the groups are equivalent.

General statistical explanation: an unadjusted p-value addresses a single comparison without accounting for other outcomes or tests. When many outcomes are examined, some results may appear noteworthy by chance even if there are no corresponding underlying differences. The record lists 48 secondary outcomes and reports no analyses; a multiplicity strategy is not reported in the registry record. This is one reason to give the secondary comparisons less weight than a prespecified primary result.

What does randomization contribute?

Randomization is intended to make assigned groups comparable on average, including on characteristics that are measured and those that are not. It supports interpreting a between-group contrast as an intervention comparison when the trial is conducted and analyzed as planned. The registry record identifies the study as randomized, but the detailed allocation procedure, analysis population, handling of missing data, and planned model are not reported in the registry record. The posted summaries alone do not show whether these aspects were handled according to a prespecified plan.

Double masking is also listed, but the registry record does not identify who was masked or describe how masking was maintained. Because the intervention consists of messages and the comparator concerns different information topics, the record's description of masking cannot establish whether participants or study personnel were unaware of group assignment.

Why can dispersion and precision matter?

General statistical explanation: when individual scores vary substantially within groups relative to the mean difference, it can be difficult to estimate a small difference precisely. The standard deviations describe this within-group spread. Precision also depends on the number of observations contributing to each arm summary and on the analysis method. A confidence interval combines information about the estimate and its uncertainty; it should be considered alongside the estimate rather than replaced by a significance label.

For outcomes with extra variability beyond what a standard model assumes, over-dispersion can make conventional uncertainty estimates too small. General statistical explanation: methods that account for over-dispersion can give more realistic standard errors and intervals. The primary outcome is reported as a continuous measure with a standard deviation, and no special over-dispersion model is reported in the registry record. There is no basis in the record to claim that such a model was needed or used.

What is and is not a recalculation?

The numerical comparison is an unadjusted recalculation from posted arm-level means, standard deviations, and sample sizes. The discrepancy indicator is false. No sponsor-reported analyses are listed, so there is no reported sponsor result to compare with the recalculation. If a sponsor analysis were reported and differed, that analysis would take precedence for describing the trial's own analysis. The planning estimates are separate from the outcome analysis and are illustrations based on the observed effect, not a measure of the trial's observed power.

11. Confidence Intervals and Precision

The primary mean difference is -0.04, with an unadjusted p-value of 0.744. Its confidence interval crosses zero, so the data do not precisely establish the direction of a primary mean difference. The arm means are close, but the interval matters: it communicates uncertainty beyond the point estimate and prevents treating -0.04 as an exact value for the underlying group contrast.

A confidence interval is most useful when read for both location and width. Its location indicates which values are compatible with the data under the calculation method, while its width reflects precision. Here, the interval includes differences favoring either group. The registry record does not report a clinical or practical threshold for an important change in intention, so the interval cannot be interpreted against such a threshold.

At follow-up, the posted vaccine-intention mean difference is 1.0, and its unadjusted p-value is <0.001. The listed interval is on the positive side of zero. This indicates a more clearly separated follow-up summary than the primary result, but it does not resolve questions about missing follow-up observations, the analysis population, or whether the comparison was part of a multiplicity-adjusted analysis. Those details are not reported in the registry record.

Precision of an estimate is not the same as importance. Even an estimate with limited statistical uncertainty would still describe a scale-based intention outcome, not actual vaccine receipt or a health outcome. Conversely, a result that does not meet a conventional significance threshold does not show that all relevant differences have been ruled out. The registry record does not report a prespecified threshold for interpreting the size of the mean difference.

12. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The planning estimates are participants per arm for 80% power and participants per arm for 90% power. They are not total sample sizes or total event counts; the event-count approach does not apply to these continuous outcomes. The registry record's planning illustration assumes a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. It uses the observed effect or a stated fraction of that effect as the effect to detect.

The 80% power column describes an assumed chance of detecting the specified effect under those planning assumptions if that effect is present. The 90% power column uses a higher target chance of detection. The registry record does not report the original design assumptions or sample-size justification used for the trial, so these figures should not be read as the trial's original target or design calculation.

The entries for smaller fractions of the observed effect require more participants per arm. This reflects a general feature of study planning: smaller differences are harder to distinguish from background variation, so more information is needed for the same target power. Planning numbers are sensitive to the effect size chosen; the observed effect may not be a reliable estimate of the effect expected in a future study.

These are planning illustrations, not observed power. They do not measure how much power the completed trial actually had, and they do not establish whether a result is valid or important. The trial's own design assumptions are not reported in the registry record.

13. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, Δ is the difference in means to detect and σ is the common standard deviation.

Worked calculation for this trial

1. Observed difference Δ = -0.040; pooled standard deviation σ = 2.845.
2. n = 2 × (1.96 + 0.842)² × 2.845² / -0.040² = 79,415.5, rounded up to 79,416 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
delta <- -0.04                      # observed difference in means
sigma <- 2.84507513468108                     # pooled standard deviation
n_per_arm <- function(power, frac = 1) {
  ceiling(round(2 * (z_a + qnorm(power))^2 * sigma^2 / (delta * frac)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (t-based, so very slightly larger)
cat("power.t.test:", round(power.t.test(delta = delta, sd = sigma, power = 0.80)$n, 1), "\n")

# Simulation: exact two-sample t-test using simulated means and variances
set.seed(6700447)
n    <- n_per_arm(0.80)
reps <- 20000
m_diff <- rnorm(reps, delta, sigma * sqrt(2 / n))             # difference in sample means
s2     <- sigma^2 * rchisq(reps, 2 * (n - 1)) / (2 * (n - 1))   # pooled sample variance
tstat  <- m_diff / sqrt(s2 * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(tstat) > qt(0.975, 2 * (n - 1))), reps))

Output from running the code

100% of observed effect: n per arm = 79,416 (80% power), 106,315 (90% power)
 75% of observed effect: n per arm = 141,184 (80% power), 189,005 (90% power)
 50% of observed effect: n per arm = 317,662 (80% power), 425,260 (90% power)
power.t.test: 79416.4 
Simulated power at n = 79,416 per arm: 0.803 (20000 replicates)

The simulation draws many sets of group means and variances at the planned sample size and counts how often the two-sample t-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

14. Multiplicity, Missing Data and Analysis Populations

The registry record lists 48 secondary outcomes, but no reported analyses. It does not report how multiplicity was handled, whether a hierarchy was specified for secondary outcomes, or whether any correction or other strategy was planned. Without that information, unadjusted secondary p-values should be treated cautiously: repeated testing can make chance findings more likely. The primary outcome is the main result for the stated primary question, but the record does not provide a complete statistical analysis plan to establish how it was intended to be analyzed.

Missing-data handling is not reported in the registry record. The primary arm summaries include 1080 and 1083 participants, while the follow-up summaries include 967 and 969. The registry record does not explain why the follow-up sample sizes differ, whether all participants were expected to complete follow-up, how missing observations were handled, or whether any sensitivity analyses were conducted. The difference in listed sample sizes should not be interpreted as evidence about the reasons for missingness.

The analysis population is also not reported in the registry record. It is not clear from the posted summaries whether the reported estimates follow an intention-to-treat approach, use another defined population, or apply any exclusions. The registry record does not report adjustment for baseline measures or other covariates, the handling of protocol deviations, or an interim-analysis plan.

These omissions limit assessment of how robust the posted comparisons are to analysis choices. They do not show that the analyses were inappropriate; they mean the relevant procedures cannot be evaluated from the registry record. The posted figures are unadjusted recalculations from summary statistics, rather than a replacement for a documented sponsor analysis.

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

The primary posted result describes a small observed difference in mean intention scores at the end of the baseline assessment: 7.81 in Control and 7.77 in the Enhanced Inoculation Message group, with a mean difference of -0.04. The confidence interval includes zero and the unadjusted p-value is 0.744. This means the posted summary does not provide clear evidence of a difference between the group means at that assessment. It does not prove that the groups are equivalent or that no effect is possible.

The follow-up summaries are more favorable to the enhanced-message group for vaccine intention and recommending the vaccine to friends. These are secondary outcomes measured at 2-4 weeks, and their interpretation is limited by the lack of reported multiplicity procedures, analysis details, and missing-data methods. They do not overturn the primary result or establish that participants later received a vaccine.

The study addresses responses to misinformation messages, not the efficacy or safety of an HIV vaccine. The endpoint is self-reported intention on a scale, and the record does not report actual vaccine uptake or HIV infection outcomes. The observed differences therefore should not be translated into claims about clinical benefit or health effects.

The findings also apply to the comparison and population represented in this study record: an enhanced inoculation message against an attention-control message among adolescent girls and young women in South Africa. The record does not report subgroup findings, so it does not establish whether results differ by sociodemographic or behavioral factors. Further, a posted summary cannot establish that the same pattern would occur in other settings or with other messages.

In short, the primary comparison is close to zero and uncertain, while the posted follow-up secondary comparisons show larger differences in favor of the enhanced-message arm. The absence of a reported sponsor analysis and key analysis details calls for a cautious reading of the estimates.

16. Why This Trial Matters Statistically

This trial is statistically informative because it distinguishes a short-term response to misinformation messaging from later outcomes. The primary measure is taken after intervention and misinformation exposure at the end of the baseline assessment, while additional measures are listed at follow-up. A difference in pattern across these time points makes it important to keep outcome timing clear rather than treating all intention measures as interchangeable.

The study also illustrates why an estimated difference, its uncertainty, and the analysis plan should be considered together. The primary difference is close to zero, its interval crosses zero, and its unadjusted p-value is 0.744. Those features describe the evidence at the primary assessment without establishing equivalence. The more separated follow-up summaries are secondary and require additional caution because multiplicity handling and missing-data methods are not reported.

For research on misinformation interventions, outcomes such as intention, credibility, and recommendations capture different dimensions of response. They can help characterize how participants react to messages, but they do not substitute for behavior or health outcomes. The registry lists several kinds of secondary measures, making transparency about outcome selection and analysis especially relevant.

The registry record does not report the planned statistical analysis or sponsor analyses. That absence limits independent assessment of whether the posted estimates match the prespecified approach. It also emphasizes the value of reporting analysis populations, missing-data procedures, and multiplicity plans alongside outcome summaries. These details are important for interpreting the strength and scope of conclusions from a randomized study.

17. 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 primary endpoint is an intention scale rather than observed vaccine receipt, and the registry record does not report actual uptake or HIV infection outcomes. The primary assessment is described as occurring after the intervention and misinformation exposure, at the end of the baseline assessment; the label may be difficult to interpret without fuller timing details. Follow-up is listed at 2-4 weeks, which provides a later measure but does not establish persistence beyond that timeframe.

The record describes the enhanced message and an attention-control condition, but the control content concerns diabetes and nutrition rather than HIV-vaccine misinformation. Although the control is described as matching message length, differences in topic and content may matter when interpreting what aspect of the messages is being compared. The registry record does not report enough detail to assess message delivery, participant engagement, or adherence.

Subgroup effects are included among the study objectives, but subgroup results are not reported in the registry record. Details of the statistical analysis, analysis population, missing-data handling, and multiplicity strategy are also not reported. The number of outcomes listed makes the absence of multiplicity information particularly relevant to interpretation of secondary results.

The posted comparisons are unadjusted recalculations from summary statistics, and no reported analyses are listed. Consequently, they do not provide the detail of a complete sponsor analysis. The study status is active, not recruiting, and the record does not describe whether all planned follow-up and analyses are complete.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Protecting Against HIV Vaccine Misinformation With Adolescent Girls and Young Women in South Africa — NCT06700447.
• Registry record last updated 2026-09-24; status last verified 2026-08.
• Results first posted 2026-08-28.
• 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.

21. Record Summary

NCT06700447 is a randomized, double-masked, parallel study sponsored by the University of Pennsylvania. It compares an enhanced HIV-vaccine inoculation message with an attention-control message about diabetes and nutrition among adolescent girls and young women in South Africa. The primary outcome is mean intention to receive an HIV vaccine on a 1-10 scale, measured after misinformation exposure at the end of the baseline assessment.

The primary posted comparison is -0.04, with means of 7.81 in Control and 7.77 in the enhanced-message group; the unadjusted p-value is 0.744 and the confidence interval includes zero. Follow-up summaries show higher vaccine-intention and recommendation-to-friends means in the enhanced-message group, but these are secondary outcomes. The registry record lists no reported analyses and does not report the analysis plan, multiplicity procedures, or missing-data methods.