Phase III Double-blind, Placebo-controlled Study of AZD7442 for Pre-exposure Prophylaxis of COVID-19 in Adult.: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Phase III Double-blind, Placebo-controlled Study of AZD7442 for Pre-exposure Prophylaxis of COVID-19 in Adult. (NCT04625725), a randomized phase 3 study. The primary outcome is Number of Participants With First Case of SARS-CoV-2 RT-PCR-positive Symptomatic Illness.

2. Clinical Question

3. Trial Design

This was a Phase III, randomized, double-blind, placebo-controlled, multicenter study in adults. The registry classifies its design as parallel-group and its masking as triple. The intended comparison was a single dose of AZD7442 against saline placebo for pre-exposure prevention of COVID-19. The registry record lists 5197 participants as enrolled. Separately, the parent-study arm descriptions give an approximate planned enrollment of 5150 with a 2:1 allocation. The approximate arm totals in those descriptions are planning figures, not a report of the final efficacy analysis population.

The study began on 2020-11-21, had a primary completion date of 2022-08-16, and is listed as completed. The primary endpoint description specifies an analysis through 165 days and a final analysis based on 183 days of follow-up. It says the required number of endpoint events was reached 165 days after the study start date, although the registry does not report the event threshold or the analysis details associated with it.

The record also describes repeat-dose sub-studies, including groups receiving AZD7442 at different repeat-dose intervals and a subset receiving additional doses. Those descriptions do not establish the results of the parent-study comparison and should not be combined with it. Further details about the randomization procedure, masking roles, study sites, eligibility criteria, adherence, and protocol deviations are not reported in the registry record.

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.

Provent Main Study

Reasons for not completing this period:

Provent Sub Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: All randomized and dosed participants who did not have a prior SARS-CoV-2 RT-PCR-positive confirmed COVID-19 infection.

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: This study is made of two parts: Main study (overall number of participants is 5197) and a Sub Study where 503 participants from the Main study took different treatments from Main Study. Total across groups is not applicable here.

Only the first 6 of 7 groups are shown.

6. Primary Endpoint

The registry lists the primary outcome as Number of Participants With First Case of SARS-CoV-2 RT-PCR-positive Symptomatic Illness, measured over 165 Days for primary analysis, 183 days for final analysis.

The primary endpoint is the number of participants with a first case of SARS-CoV-2 RT-PCR-positive symptomatic illness. It combines a laboratory-confirmed infection criterion, identified by RT-PCR, with the presence of symptomatic illness. Counting first cases avoids counting multiple episodes in the same participant as separate first events for this endpoint. The stated endpoint population consists of randomized and dosed participants without a prior confirmed SARS-CoV-2 RT-PCR-positive COVID-19 infection.

The endpoint was intended to estimate the efficacy of a single intramuscular dose of AZD7442 compared with placebo for prevention of COVID-19 before Day 183. The record gives distinct time windows: 165 days for the primary analysis and 183 days for the final analysis. It explains that the event requirement for the primary endpoint was reached after 165 days, while the final analysis uses the planned 183 days of follow-up. These are analysis windows, not treatment-effect estimates.

For a binary endpoint, an event count can describe how many participants experienced the outcome, but the count alone does not establish the size or precision of a between-group difference. The registry record does not report the primary endpoint counts by group, a treatment-effect estimate, a confidence interval, or a p-value.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry describes a randomized parallel-group comparison of AZD7442 and placebo. Randomization is intended, in general, to make treatment groups comparable at assignment with respect to measured and unmeasured characteristics. Masking can reduce the influence of expectations on participant experience, clinical management, and outcome assessment. The record classifies masking as triple and the study as double-blind in its title, but does not report which people or roles were masked or the procedures used to maintain masking.

What does a count endpoint represent?

The primary outcome is a count of participants with a first case of symptomatic illness confirmed by SARS-CoV-2 RT-PCR. The registry identifies the endpoint unit as participants and describes it as a count. In general, a binary participant-level outcome records whether each person did or did not experience the defined event during the relevant follow-up. Group event counts are often interpreted alongside the number of participants assessed in each group, because a count without its denominator does not describe the frequency of the event. Neither the group-specific primary event counts nor endpoint denominators are reported in the registry record.

The endpoint requires both symptomatic illness and a positive RT-PCR result. Consequently, it is not simply a count of all infections, all positive tests, or all respiratory symptoms. The definition focuses on first cases, so repeated episodes in one participant are not represented as additional first cases for this measure. The record does not report further endpoint adjudication details, the symptom definition, testing schedules, or procedures for handling uncertain cases.

How should the analysis windows be read?

The endpoint description gives 165 days for the primary analysis and 183 days for the final analysis. It states that the number of events required for the primary endpoint was achieved after 165 days and that the final analysis used the planned 183 days of follow-up. In general, extending follow-up can allow additional outcomes to accrue, but the relationship between the two analyses depends on the prespecified analysis plan and the observed event pattern. The registry record does not report the primary event threshold, the analysis plan, or results from either time window. The dates and windows alone do not determine the treatment effect.

The study is described as randomized, but the statistical analysis details are not reported in the registry record. The record does not identify the effect measure used for the primary comparison, whether the analysis was adjusted, how follow-up time was accounted for, or how protocol deviations were handled. A general distinction is useful: an unadjusted comparison summarizes group outcomes without model-based adjustment, whereas an adjusted analysis uses specified covariates or other model structure. No particular adjusted or unadjusted approach can be attributed to this trial from the available record.

What do confidence intervals and p-values add?

General explanation: a point estimate gives a single summary of the contrast between groups, while a confidence interval communicates uncertainty around that estimate under the chosen method. A narrower interval indicates greater precision under that method; an interval that spans values with materially different interpretations may leave substantial uncertainty. A p-value is calculated relative to a specified statistical model and null hypothesis. It is not a measure of clinical importance and does not indicate the probability that a treatment effect is real. The registry record does not report a primary effect estimate, confidence interval, or p-value, so these features cannot be assessed for the trial’s primary comparison.

The record describes five analyses and eight outcome measures, and lists secondary outcomes concerning post-treatment SARS-CoV-2 nucleocapsid antibodies, severe or critical symptomatic illness, COVID-19-related emergency department visits, serum AZD7442 concentrations and pharmacokinetic parameters if data permit, and anti-drug antibodies. Listing several analyses and outcomes raises general questions about multiplicity: when multiple hypotheses are assessed, the chance of at least one chance-positive finding can increase if no adjustment or hierarchy is used. The registry does not report a multiplicity strategy, the analysis hierarchy, or which results correspond to the listed analyses. No adjustment method should be inferred.

The registry’s planning illustration assumptions state a two-sided significance level of 0.05, equal allocation between arms, and a normal approximation, with the effect to detect described as a stated fraction of the observed effect. Those are assumptions for planning illustrations, not a report of the trial’s original design justification. The record does not report the trial’s own sample-size justification or the effect size used in the illustration. Such illustrations are not a measure of achieved power and do not replace the observed estimate and its uncertainty.

General explanation: over-dispersion matters when outcome variability is greater than a model assumes, because standard errors may then be too small and confidence intervals too narrow if the extra variability is ignored. For this participant-level binary endpoint, the registry record does not report a model or dispersion assessment; over-dispersion should not be assumed to have been present or addressed. Likewise, no particular regression model, covariate adjustment, interim-analysis method, or missing-data method is reported in the registry record.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists eight outcome measures and five analyses, including the primary endpoint and secondary outcomes. The secondary outcomes include post-treatment responses for SARS-CoV-2 nucleocapsid antibodies, severe or critical symptomatic illness, COVID-19-related emergency department visits, serum AZD7442 concentrations and pharmacokinetic parameters if data permit, and anti-drug antibodies. The record does not explain how these outcomes were ordered, which comparisons were confirmatory, or whether any multiplicity adjustment was used. Without that information, results across multiple outcomes should not be treated as though they each arose from a single prespecified test.

The primary endpoint description defines a population of randomized and dosed participants with no prior confirmed infection. It does not report how many people met that definition, how many had outcome data at each analysis time, or how missing or incomplete follow-up was handled. The registry record also does not report how participants who discontinued, were lost to follow-up, or had protocol deviations were treated in the analysis.

The record does not give details of an intention-to-treat analysis, a per-protocol analysis, imputation, censoring, sensitivity analyses, or assumptions about missing outcomes. These methods can affect interpretation when outcome status is unavailable, but no specific approach can be attributed to this study based on the registry record. The record also does not report a prespecified analysis hierarchy or whether the primary and final analyses were both treated as confirmatory. These omissions limit assessment of how multiplicity and missing data may have affected the reported evidence.

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.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: acute kidney injury (2.7%), covid-19 (2.6%), pneumonia (2.6%), covid-19 pneumonia (2.5%), metabolic encephalopathy (1.7%).

The registry lists participants at risk and participants affected by serious adverse events for the AZD7442 and placebo groups, as well as three additional sub-study groups. For AZD7442, 3461 participants were listed at risk and 215 were affected; for placebo, 1736 were listed at risk and 97 were affected. The record also lists Group 1 with 234 at risk and 31 affected, Group 2 with 119 at risk and 20 affected, Group 3a with 76 at risk and 12 affected, and Group 3b with 74 at risk and 12 affected. These are group-specific counts, and the additional groups are not interchangeable with the parent-study arms.

Deaths are separately listed as 22 for AZD7442, 10 for placebo, 8 for Group 1, 5 for Group 2, 0 for Group 3a, and 1 for Group 3b. The record does not report further detail about how deaths relate to serious adverse events or the timing and attribution of these events. Counts alone do not establish that an event was caused by a study intervention.

The registry’s serious-event terms include acute kidney injury at 2.7%, Covid-19 at 2.6%, pneumonia at 2.6%, Covid-19 pneumonia at 2.5%, metabolic encephalopathy at 1.7%, and pulmonary embolism at 1.7%. The record does not specify the denominator or clarify whether these terms overlap. These figures should therefore be read as listed terms and percentages, not as a direct comparison between randomized groups. Other-event counts are also listed, but event definitions, severity thresholds, and follow-up details are not reported in the registry record.

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

The registry record establishes that the study was designed to compare AZD7442 with saline placebo for pre-exposure prevention of COVID-19 in adults, using first symptomatic SARS-CoV-2 RT-PCR-positive illness as the primary endpoint. It also states that the primary analysis covered 165 days and the final analysis used 183 days of follow-up. These details describe the question and the analysis windows, not the result of the comparison.

The primary endpoint counts by group and the treatment-effect estimate are not reported in the registry record. Without those results, it is not possible to state from this record how the groups differed, how large any difference was, or how precise the estimate was. The same limitation applies to claims about statistical significance or the consistency of findings across the primary and final analyses. A study’s completed status and enrollment total do not supply the missing efficacy results.

General explanation: a trial result applies most directly to its stated population, intervention, comparator, endpoint, and follow-up. Here, the primary endpoint population excludes participants with a prior confirmed SARS-CoV-2 RT-PCR-positive COVID-19 infection and includes randomized and dosed participants. The result, if reported elsewhere, would need to be interpreted in light of those definitions and the methods used to handle follow-up and missing data. Those method details are not reported in the registry record.

The safety listings provide descriptive counts for the named groups, along with several serious-event terms and percentages. They do not, on their own, establish causal attribution or provide a complete comparative assessment of safety. The registry record does not report enough detail about event timing, attribution, or the denominators behind the listed serious-event percentages to resolve those questions.

Accordingly, the record supports a description of the trial’s design, endpoints, and selected safety summaries. It does not support a treatment conclusion. Interpretation of the efficacy question requires the group-level primary outcome results and their uncertainty, while broader interpretation also depends on analysis methods and missing-data information that are not reported in the registry record.

13. Why This Trial Matters Statistically

Statistically, the trial is notable for its randomized, masked, placebo-controlled comparison and for a primary endpoint that requires both symptoms and RT-PCR confirmation. Randomization provides a basis for comparing outcomes between groups, while masking is intended in general to limit influences on behavior and outcome assessment. The registry classifies the study as Phase III, multicenter, parallel-group, and triple-masked. These design features describe the intended structure of the evidence; they do not replace the observed comparison.

The endpoint description also distinguishes an analysis at 165 days from a final analysis based on 183 days of follow-up. The record says the event requirement for the primary endpoint was achieved after 165 days. That makes the distinction between the primary and final analysis windows important when interpreting results, but the event requirement and the results for both windows are not reported in the registry record.

The record’s planned 2:1 allocation and the actual enrollment listing of 5197 illustrate why planned design quantities and final analysis quantities should not be conflated. The primary endpoint population is narrower than overall enrollment, and its analyzed denominators are not reported. The safety listings also include sub-study groups, which should remain distinct from the parent-study comparison.

Finally, the record lists multiple outcomes and analyses but does not report how multiplicity, missing data, or analysis populations were handled. These are central statistical considerations: they affect how confidently findings can be interpreted and how broadly they can be generalized. Because primary efficacy estimates and key analysis details are absent, the statistical importance of the trial lies in its clearly defined comparison and endpoint, while the magnitude and precision of its findings remain unavailable in the registry record.

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 this trial from the registry record is that primary efficacy results are not reported. There are no group-specific primary event counts, effect estimate, confidence interval, or p-value. The stated endpoint and follow-up windows therefore cannot establish the magnitude or precision of the AZD7442-versus-placebo comparison.

The registry describes the primary analysis at 165 days and the final analysis using 183 days of follow-up, but does not report the event threshold, detailed analysis plan, or results for either window. It is also unclear from the record how the primary analysis population was formed in practice: the endpoint population is defined, but the number of participants meeting that definition and the analyzed denominators are not reported.

Important design and analysis details are not reported in the registry record, including eligibility criteria beyond the primary endpoint population description, baseline characteristics, randomization procedures, roles covered by triple masking, outcome adjudication procedures, missing-data handling, protocol deviations, covariate adjustment, and multiplicity control. The record also does not report the trial’s own sample-size justification, interim-analysis procedures, or a detailed statistical analysis plan.

Safety interpretation has additional limits. The serious adverse-event listings include parent-study and sub-study groups, and the registry does not specify the denominator behind the listed serious-event percentages or whether the terms overlap. Timing, attribution, and event definitions are not described in detail. These omissions limit direct comparisons and causal interpretation of the safety summaries.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Phase III Double-blind, Placebo-controlled Study of AZD7442 for Pre-exposure Prophylaxis of COVID-19 in Adult. — NCT04625725.
• Registry record last updated 2024-12-31; status last verified 2024-12.
• Results first posted 2022-12-20.
• 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

NCT04625725 is a completed Phase III randomized, triple-masked, parallel-group study comparing AZD7442 with saline placebo for pre-exposure prevention of COVID-19 in adults. The record lists enrollment of 5197, a start date of 2020-11-21, and a primary completion date of 2022-08-16. The parent-study plan describes an approximate 2:1 allocation and a single 300 mg AZD7442 dose given by two intramuscular injections.

The primary endpoint is the number of participants with a first case of symptomatic SARS-CoV-2 RT-PCR-positive illness among randomized and dosed participants without prior confirmed infection. The endpoint description distinguishes a 165-day primary analysis from a final analysis based on 183 days of follow-up. The primary efficacy counts and comparative estimate are not reported in the registry record. Safety listings include serious-event counts, deaths, and selected serious-event terms, but do not provide enough detail for full comparative interpretation.