Safety, Tolerability, and Immunogenicity Study of Homologous Ad26 Mosaic Vector Vaccine Regimens or Heterologous Ad26 Mosaic and MVA Mosaic Vector Vaccine Regimens With Glycoprotein 140 (gp140) for Human Immunodeficiency Virus (HIV) Prevention: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Safety, Tolerability, and Immunogenicity Study of Homologous Ad26 Mosaic Vector Vaccine Regimens or Heterologous Ad26 Mosaic and MVA Mosaic Vector Vaccine Regimens With Glycoprotein 140 (gp140) for Human Immunodeficiency Virus (HIV) Prevention (NCT02315703), a randomized phase 1, phase 2 study. The primary outcome is Percentage of Participants With Solicited Local Adverse Events (AEs) Post Vaccination.

2. Clinical Question

3. Trial Design

The registry record describes a randomized, double-blind, parallel-group Phase 1/2a trial that is completed. Enrollment was 393, and the listed condition was healthy. The study began on 2014-12-22, with primary completion on 2017-08-29. Janssen Vaccines & Prevention B.V. is listed as sponsor.

Eight groups received different regimens. Groups 1 through 3 used Ad26.Mos.HIV with high-dose gp140, low-dose gp140, or no gp140 in the later regimen. Groups 4 through 6 used Ad26 followed by MVA-Mosaic, with high-dose gp140, low-dose gp140, or placebo injection. Group 7 received Ad26 and high-dose gp140, while Group 8 received placebo injections. The registry descriptions give vaccination timing for several regimens, including Weeks 0 and 12 for initial injections and Weeks 24 and 48 for later injections in several groups. The Group 1 arm description is incomplete in the registry record, so its full schedule is not reported there.

The primary outcome was the percentage of participants with solicited local adverse events, collected within 7 days after vaccination and followed up to Week 49. The primary analysis population was the FAS, defined as randomized participants with at least one documented study vaccine administration, regardless of protocol deviations. Arm denominators for the endpoint range among the reported values of 48, 49, and 50 participants.

The registry also lists six secondary immunogenicity outcome categories, including binding antibody, neutralizing antibody, phagocytosis, and T-cell response measures. Results for those secondary outcomes are not reported in the registry record. The registry record does not report the original sample-size justification, planned statistical analysis details, or an interim-analysis plan.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Only the first 6 of 8 groups are shown.

Main Study (From Week 0 up to Week 96)

Reasons for not completing this period:

LTE (After Week 96 up to Week 336)

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: The FAS included all randomized participants with at least one study vaccine administration documented regardless of the occurrence of protocol deviations.

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 9 groups are shown.

6. Primary Endpoint

The registry lists the primary outcome as Percentage of Participants With Solicited Local Adverse Events (AEs) Post Vaccination, measured over Up to Week 49 (7 days post any dose).

The primary endpoint is the percentage of participants with solicited local adverse events after vaccination, up to Week 49 and within 7 days after any dose. Events were injection-site erythema, induration, swelling, itching, and warmth. A participant-level percentage describes how often at least one specified event was reported under the endpoint definition; it does not describe how many events each participant experienced or how severe they were.

This kind of endpoint is used to describe local tolerability. It is clinically distinct from an immunogenicity endpoint, which measures immune responses, and from an efficacy endpoint, which would assess prevention of HIV infection. The registry’s primary endpoint therefore supports a comparison of reported local reactions across the study regimens and placebo, not a conclusion about prevention of HIV.

The denominator is the arm-specific number of participants included in the endpoint result, and the numerator is the number recorded as affected. For example, Group 1 had 44 affected participants among 50, and Group 8 had 28 among 49. The percentages are the reported arm results. The endpoint population was the FAS, not necessarily every person enrolled: participants had to be randomized and have at least one documented vaccine administration to be included. The registry record does not report further detail about how missing endpoint observations were handled.

7. Results Posted in the Registry

• Group 1: Ad26/Ad26 + gp140 High Dose (HD): 88.0% (44/50) versus 57.1% (28/49) on control; risk difference 30.9 percentage points (95% CI 14.3 to 47.4), risk ratio 1.54 (1.18–2.00); unadjusted two-proportion z-test p = <0.001.
• Group 2: Ad26/Ad26 + gp140 Low Dose (LD): 83.7% (41/49) versus 57.1% (28/49) on control; risk difference 26.5 percentage points (95% CI 9.2 to 43.8), risk ratio 1.46 (1.12–1.92); unadjusted two-proportion z-test p = 0.004.
• Group 3: Ad26/Ad26: 75.5% (37/49) versus 57.1% (28/49) on control; risk difference 18.4 percentage points (95% CI 0.0 to 36.7), risk ratio 1.32 (0.99–1.77); unadjusted two-proportion z-test p = 0.054.
• Group 4: Ad26/MVA + gp140 HD: 77.1% (37/48) versus 57.1% (28/49) on control; risk difference 19.9 percentage points (95% CI 1.7 to 38.2), risk ratio 1.35 (1.01–1.80); unadjusted two-proportion z-test p = 0.037.

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is binary at the participant level: a participant either met the definition of having a solicited local adverse event or did not. The reported percentage is a proportion expressed as a percentage. Its denominator is the arm-specific number of participants in the endpoint population, and its numerator is the number affected. This makes the result easy to interpret as frequency, while leaving out details such as event severity, duration, or repeated events unless those are reported separately.

What does a risk difference express?

A risk difference compares two proportions by subtracting the reference-arm proportion from the other arm’s proportion. A positive estimate means the observed proportion was higher in the compared arm than in the reference arm; a negative estimate would mean it was lower. The posted comparisons use Group 8, with 57.1% affected, as the reference for each active-regimen group. The risk-difference estimates are on the proportion scale, so they should not be confused with an odds ratio or a relative risk.

Risk differences are often useful because they express an absolute contrast in the outcome frequency. Relative measures answer different questions: a risk ratio compares proportions as a ratio, while an odds ratio compares odds. These measures can tell different numerical stories, especially when outcomes are common. The registry record includes relative measures in addition to risk differences, but the main interpretation emphasizes the risk difference and its interval.

What do confidence intervals and p-values add?

A confidence interval describes the uncertainty around an estimate under the method used to construct it. It gives a range of values compatible with the observed data and that method’s assumptions; it does not guarantee that the true value lies in that particular interval. For a risk difference, an interval that spans zero includes no difference among the values compatible with the interval calculation. The Group 7 comparison interval spans zero. The intervals for the other comparisons are reported on the positive side of zero, including the Group 3 interval whose lower bound is very close to zero.

A p-value measures how unusual data at least as incompatible with a stated null model would be if that model and the test assumptions held. It does not measure the probability that the null is true, and it does not measure clinical importance. The posted p-values are unadjusted. Their interpretation does not account for the fact that several regimen groups were compared with the same placebo group.

Why can small arms produce uncertain estimates?

With a binary outcome, each participant contributes an affected or unaffected result. When an arm has a limited denominator, changing the result for a small number of participants can move the estimated percentage noticeably. That sampling variability is reflected in the comparison intervals. In general, larger samples can improve precision, but they do not remove bias, measurement problems, or limitations in how representative the participants are.

There are also design features that matter to interpretation. Random allocation can support fairer comparisons by reducing systematic differences between groups at baseline, while masking can reduce some forms of behavior or assessment bias. Those design features do not guarantee identical groups in a finite trial or eliminate the effects of missing observations. The registry record describes randomization and double masking but does not report the allocation procedure, masking details, or handling of missing primary endpoint data.

What does an unadjusted comparison leave out?

An unadjusted comparison uses the observed arm summaries without accounting for other variables. It is a straightforward contrast, but it does not tell whether an adjusted analysis would differ. The registry record does not report an adjustment model for the primary outcome. The posted recalculated results are based on the available summary counts, and the record marks no discrepancy between those calculations and the reported summary data.

Multiple comparisons also matter. When many hypotheses are tested, the chance of at least one apparently unusual result can increase if each test is treated independently at a conventional threshold. A multiplicity method can address that issue, but whether one was planned or used is not reported in the registry record. Therefore, the p-values should be read as individual, unadjusted comparisons rather than as multiplicity-controlled evidence across the set of regimens.

Finally, the outcome is specific to solicited local events recorded within the stated post-vaccination window. It is not a comprehensive measure of all possible safety outcomes. The record separately lists serious adverse event counts and secondary immunogenicity outcome categories, but those address different questions and should not be combined with the primary local-event percentage as though they were the same endpoint.

10. Confidence Intervals and Precision

The arm percentages are estimates from the participants included in each result, not exact population rates. The comparison confidence intervals show how much uncertainty remains around the risk-difference estimates. They are not all equally wide, which means precision varies across comparisons. The arm denominators reported for the endpoint are 48, 49, or 50 participants, so the estimates are based on relatively small groups.

The intervals for Groups 1, 2, 3, 4, 5, and 6 are on the positive side of zero, with the Group 3 lower bound very close to zero. The Group 7 interval spans zero. This describes interval location, not a guarantee about the true effect. In particular, an interval that spans zero does not prove equivalence, and an interval that does not span zero does not by itself establish clinical importance.

Confidence intervals help distinguish the point estimate from its precision. A point estimate gives one value for the observed contrast; the interval gives a range of values compatible with the data under the calculation method. Wider intervals indicate less precision, while narrower intervals indicate more precision. They do not account for every possible source of uncertainty, such as bias, missing data, outcome measurement, or multiplicity.

Since these comparisons are unadjusted and the registry record does not report a multiplicity plan, the intervals should be read as individual comparison intervals. They do not necessarily provide simultaneous coverage across all seven comparisons. A reader should consider the size of each observed contrast, its interval, the small arm denominators, and the unadjusted nature of the analysis together rather than relying on a p-value alone.

11. 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 figures are participants per arm for each two-arm comparison, not total event counts. They are illustrations calculated from the observed effect, not the trial’s original design assumptions. The registry record does not report the trial’s own sample-size justification.

The planning assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect to detect is set as a stated fraction of the observed effect. For example, the Group 1 comparison lists 32 participants per arm for 80% power and 42 participants per arm for 90% power when planning for 100% of the observed effect. When planning for 75% of that effect, the corresponding figures are 62 and 83 participants per arm; for 50%, they are 150 and 200 participants per arm.

In plain language, the 80% power column gives the illustrated number of participants per arm for a design with an 80% chance of detecting the assumed effect under the stated calculation assumptions. The 90% power column uses a higher chance of detection, which generally calls for more participants under the same assumptions. These figures are planning illustrations, not observed power.

Smaller effects are harder to distinguish from random variation, so planning to detect a smaller fraction of the observed effect requires more participants per arm in these illustrations. The curve should be read in the same spirit: it relates the assumed effect size to the sample size implied by the planning assumptions, rather than forecasting what a future trial will observe. The calculations do not establish that the assumed effects are realistic, and they do not replace an original design rationale, which is not reported in the registry record.

12. 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, p₀ and p₁ are the control and treatment proportions, and p̄ is their average.

Worked calculation for this trial

1. Control proportion p₀ = 0.571; treatment proportion p₁ = 0.880; average p̄ = 0.726.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.6310 = 1.2367.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.5920 = 0.4983.
4. n = (1.2367 + 0.4983)² / (0.3086)² = 31.6, rounded up to 32 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
p0 <- 0.571428571428571                          # control proportion
p1 <- 0.88                          # treatment proportion
n_per_arm <- function(power, frac = 1) {
  q1 <- p0 + (p1 - p0) * frac               # smaller effect = fraction of the observed difference
  pbar <- (p0 + q1) / 2
  z_b <- qnorm(power)
  ceiling(round((z_a * sqrt(2 * pbar * (1 - pbar)) + z_b * sqrt(p0 * (1 - p0) + q1 * (1 - q1)))^2 / (q1 - p0)^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 (unrounded n per arm)
cat("power.prop.test:", round(power.prop.test(p1 = p0, p2 = p1, power = 0.80)$n, 1), "\n")

# Simulation: how often does the z-test reject at the 80%-power sample size?
set.seed(2315703)
n    <- n_per_arm(0.80)
reps <- 20000
x0 <- rbinom(reps, n, p0); x1 <- rbinom(reps, n, p1)
ph <- (x0 + x1) / (2 * n)
z  <- ((x1 - x0) / n) / sqrt(ph * (1 - ph) * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(z) > z_a, na.rm = TRUE), reps))

Output from running the code

100% of observed effect: n per arm = 32 (80% power), 42 (90% power)
 75% of observed effect: n per arm = 62 (80% power), 83 (90% power)
 50% of observed effect: n per arm = 150 (80% power), 200 (90% power)
power.prop.test: 31.6 
Simulated power at n = 32 per arm: 0.824 (20000 replicates)

The simulation draws many pairs of event counts at the planned sample size and counts how often the two-proportion z-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.

13. Multiplicity, Missing Data and Analysis Populations

The registry record reports seven unadjusted comparisons of active-regimen groups with Group 8 for the primary local adverse event endpoint. No multiplicity adjustment is reported. When several comparisons are made, interpreting each p-value against a conventional threshold without accounting for the family of comparisons can increase the chance of an apparently notable result arising by chance. This is a general statistical concern; the record does not state what multiplicity strategy, if any, was prespecified.

The record lists six secondary immunogenicity outcome categories, including antibody and T-cell response measures, but their numerical results are not reported in the registry record. The record also reports no analysis records for those outcomes. It therefore does not allow an assessment of how primary and secondary endpoints were prioritized, whether secondary analyses were adjusted for multiple testing, or how those results compare across regimens.

The primary analysis population is the FAS: randomized participants with at least one documented study vaccine administration, regardless of protocol deviations. This definition excludes randomized participants without a documented vaccine administration. The endpoint denominators are reported by arm, but the registry record does not describe the amount or pattern of missing endpoint data or how missing observations were handled.

Randomization and double masking are reported design features, but further details about allocation concealment, masking procedures, or the primary statistical model are not reported in the registry record. The record does not state whether the primary comparison was intended to be adjusted for baseline characteristics, whether there were interim analyses, or what formal analysis plan governed the p-values. Those unknowns limit assessment of the analysis strategy; they should not be filled in by assumption.

14. 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.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: myocardial infarction (2.1%), hiv infection (2.1%), pyelonephritis (2.1%), generalised anxiety disorder (2.1%), major depression (2.1%).

The registry reports serious adverse events by group, with both the number at risk and the number affected. The affected counts are 8 in Group 1, 3 in Group 2, 3 in Group 3, 4 in Group 4, 4 in Group 5, 5 in Group 6, 2 in Group 7, and 5 in Group 8. The respective at-risk group sizes are 50, 49, 49, 48, 49, 49, 50, and 49. No deaths are reported in any group.

These serious adverse event figures are distinct from the primary endpoint, which concerns solicited local events within 7 days after vaccination. A serious adverse event count does not identify whether an event was caused by the study intervention. The registry also lists serious-event terms with percentages, including Myocardial Infarction, Hiv Infection, Pyelonephritis, Generalised Anxiety Disorder, Major Depression, and Mallory-Weiss Syndrome. The registry record does not provide enough context in these figures to infer causality or compare event rates by type across groups.

Counts should be read with their denominators and the study’s follow-up context. They are descriptive safety reports, not evidence that a regimen caused or prevented a particular event. The registry record does not report further detail on the timing, relationship assessment, or clinical course of these serious events in the listed summary.

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

The primary result describes how often participants reported solicited local adverse events under the trial’s specified definition and follow-up window. The reported percentages were higher in each active-regimen group than in the placebo group. The unadjusted comparison estimates are positive, with the Group 7 interval spanning zero and other reported comparison intervals on the positive side. This is a description of the posted results, not a conclusion that any regimen caused a particular participant’s symptoms.

The endpoint is limited to injection-site erythema, induration, swelling, itching, and warmth collected within 7 days after vaccination, with follow-up up to Week 49. It does not summarize every possible adverse event, long-term safety, immune response, or HIV infection. The separate serious adverse event counts address a different safety summary, and the secondary outcome categories address immunogenicity. Their results cannot be inferred from the local-event endpoint.

The results also do not establish that one vaccine regimen is clinically preferable. A higher local-event percentage is not, by itself, a complete measure of benefit or harm. The trial’s stated purpose included safety, tolerability, and comparison of envelope-binding antibody responses, but the primary results do not show whether immune responses differed or whether HIV was prevented. The registry record does not report the secondary outcome values needed to assess those questions.

Finally, the comparisons are unadjusted and involve multiple regimen groups. Their p-values do not account for multiplicity in the posted calculations, and the registry record does not report whether an adjustment was planned. The arm-specific estimates are also based on relatively small denominators and have uncertainty, as reflected in the confidence intervals. They are best read as evidence about the observed participants and endpoint, with these limits in mind, rather than as definitive estimates for all populations or settings.

16. Why This Trial Matters Statistically

This trial presents several regimens in a parallel-group randomized design, making clear how a binary safety endpoint can be summarized across multiple arms. The primary outcome is a participant-level percentage, so the numerator and denominator have direct meaning: the number affected among the participants included in that arm’s endpoint result. The registry also presents comparisons with a placebo group, allowing absolute differences and their uncertainty to be considered alongside the arm percentages.

Statistically, the comparison set highlights why a single p-value should not carry the interpretation. Seven active-regimen comparisons are reported, and the p-values are unadjusted. The estimates, intervals, and multiplicity context all matter. The Group 3 comparison is a useful reminder that an interval close to zero and a p-value near a commonly used reference value require careful reading rather than a binary declaration. The Group 7 interval spanning zero likewise does not establish equivalence.

The trial also separates safety from immunogenicity. Its listed secondary outcomes include several antibody and T-cell response measures, but their values are not reported in the registry record. This makes the boundary of the available evidence important: the local adverse event results can describe tolerability signals, but they cannot answer the broader immunogenicity or prevention questions.

Finally, the small arm denominators make precision and planning relevant. The planning illustrations show how assumptions about the effect to detect influence the participants per arm required, but those illustrations are not the original study rationale or a measure of the trial’s observed power. Together, these features make the record a useful example of interpreting percentages, unadjusted comparisons, uncertainty, safety summaries, and missing statistical-plan details without extending the conclusions beyond the reported endpoint.

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.
• Participant counts were reconstructed from posted percentages and arm sizes, so small rounding differences are possible.

The primary endpoint captures a defined set of solicited local events, and does not represent all safety outcomes. It concerns events collected within 7 days after any dose, with follow-up up to Week 49. The registry record does not report severity-specific primary endpoint results or further details about duration and recurrence, so the percentage affected cannot describe those aspects of tolerability.

Arm denominators are relatively small, and the resulting estimates have uncertainty. The comparison calculations are unadjusted, and no multiplicity adjustment is reported despite comparisons across several active regimens. The registry record does not report the original analysis plan, the primary testing procedure, adjustment for baseline characteristics, or handling of missing endpoint data. These omissions make it difficult to assess whether the posted comparisons match a prespecified analysis strategy.

The endpoint population requires at least one documented vaccine administration, so it is not defined as all randomized participants. The record does not provide enough information to assess the extent or consequences of exclusions or missing observations. Although the trial is described as randomized and double-blind, details of the allocation and masking procedures are not reported.

The registry lists six secondary immunogenicity outcome categories, but their numerical results are not reported in the registry record. The serious adverse event summary provides affected counts and listed terms, but the record does not report event-level timing, relatedness, or clinical context in the summary. These limits restrict interpretation to the reported local-event endpoint and descriptive safety counts; they do not support conclusions about immune response, HIV prevention, or causation.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Safety, Tolerability, and Immunogenicity Study of Homologous Ad26 Mosaic Vector Vaccine Regimens or Heterologous Ad26 Mosaic and MVA Mosaic Vector Vaccine Regimens With Glycoprotein 140 (gp140) for Human Immunodeficiency Virus (HIV) Prevention — NCT02315703.
• Registry record last updated 2025-02-04; status last verified 2025-01.
• Results first posted 2020-11-04.
• 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

NCT02315703 is a completed randomized, double-blind, parallel-group Phase 1/2a trial sponsored by Janssen Vaccines & Prevention B.V. It enrolled healthy participants to evaluate regimens using Ad26.Mos.HIV, MVA-Mosaic, gp140 with adjuvant, and placebo. The primary outcome was the percentage of participants with solicited local adverse events after vaccination, up to Week 49.

Reported local-event percentages ranged from 70.0 in Group 7 to 88.0 in Group 1; the placebo group result was 57.1. The registry reports unadjusted comparisons of each active group with placebo, with confidence intervals and p-values. The record also lists serious adverse event counts and secondary immunogenicity outcome categories. Results for those secondary categories, the original sample-size justification, and key details of the statistical analysis plan are not reported in the registry record.