This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for Study to Evaluate the Safety and Effectiveness of Zostavax™ in Subjects 50 - 59 Years of Age (V211-022) (NCT00534248), a randomized phase 3 study. The primary outcome is Incidence of Confirmed Herpes Zoster (HZ) Cases by Vaccination Group.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT00534248 |
| Phase | Phase 3 |
| Condition | Shingles |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | Double |
| Enrollment | 22439 |
| Arms in the primary outcome | 2 |
| Lead sponsor | Merck Sharp & Dohme LLC |
| Results posted | Yes |
2. Clinical Question
Population
Participants were ages 50-59 and enrolled in a study concerning shingles. The primary analysis population was the intent-to-treat population, defined in the registry record as all participants randomized according to their planned treatment assignment. The record gives an enrollment of 22439.
Intervention
Participants assigned to the intervention received Zoster Vaccine, Live (Zostavax™). The primary endpoint description concerns confirmed herpes zoster cases following vaccination.
Comparator
Participants assigned to the comparator received placebo. The reported primary comparison uses the incidence rate in the Zostavax™ group relative to the placebo group.
Primary question
Over 2 Years, what was the incidence of confirmed herpes zoster cases per 1000 person-years in each vaccination group, and what was the estimated relative reduction in incidence rate for Zostavax™ compared with placebo?
This is a question about observed disease incidence in the randomized groups and the comparative estimate reported for those groups. Incidence is expressed relative to person-time, rather than as a simple count alone, because participants may contribute different amounts of follow-up. The registry defines vaccine efficacy for herpes zoster as the relative reduction in incidence rate in the Zostavax™ group compared with placebo, based on the intent-to-treat population.
The primary question is distinct from the secondary questions. Those concern the varicella-zoster virus antibody response at 6 weeks post vaccination and participants reporting one or more serious adverse experiences during the 42-day postvaccination follow-up period. The antibody outcome concerns an immune response, while the primary endpoint concerns confirmed clinical cases. The registry record does not establish that the antibody outcome substitutes for or predicts the primary clinical outcome.
3. Trial Design
The registry describes a Phase III, randomized, double-masked, parallel-group trial sponsored by Merck Sharp & Dohme LLC. The study title identifies adults ages 50-59, and the condition listed is shingles. Participants were assigned to Zostavax™ or placebo. The record gives an enrollment of 22439 and a completed study status.
The recorded study start is 2007-10, and the primary completion is 2010-01. The primary endpoint timeframe is 2 Years. Those dates and the endpoint timeframe describe distinct aspects of the record: the dates mark study milestones, while the timeframe specifies the period associated with the primary outcome.
Randomization creates a planned comparison between assigned groups. Double masking is a design feature intended to limit the influence of knowledge of assignment on trial conduct or outcome assessment, although the specific masking procedures and which roles were masked are not reported in the registry record. The parallel model means the record describes groups receiving their assigned study treatment rather than a crossover comparison. Further details of allocation procedures, stratification, concealment, adherence, and follow-up procedures are not reported in the registry record.
The primary analysis population is intent-to-treat: all randomized participants are analyzed according to their planned treatment assignment, as defined in the registry record. That definition preserves the randomized-group comparison, but does not itself explain how unavailable follow-up, protocol deviations, or missing outcome information were handled. Those details are not reported in the registry record.
The registry lists a vaccine and placebo intervention and reports three outcome measures and three analyses. It also lists two secondary outcomes: antibody response at 6 weeks post vaccination and serious adverse experiences during the 42-day postvaccination follow-up. The record does not report the rationale for the enrollment target, whether interim analyses were conducted, or a detailed statistical 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.
Overall Study
| Stage | Zostavax™ | Placebo |
|---|---|---|
| STARTED | 11211 | 11228 |
| VACCINATED | 11186 | 11210 |
| COMPLETED | 10550 | 10555 |
| NOT COMPLETED | 661 | 673 |
Reasons for not completing this period:
| Reason | Zostavax™ | Placebo |
|---|---|---|
| Adverse Event | 19 | 29 |
| Lost to Follow-up | 353 | 375 |
| Other protocol specified criteria | 13 | 3 |
| Physician Decision | 10 | 7 |
| Protocol Violation | 3 | 4 |
| Withdrawal by Subject | 263 | 255 |
Analysis population for the primary outcome, as defined in the registry: Intent-to-treat population defined as all participants randomized in the study according to the planned treatment, Zostavax or placebo, they were assigned.
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.
| Characteristic | Unit | Zostavax™ | Placebo | Total |
|---|---|---|---|---|
| Participants analysed | 11211 | 11228 | 22439 | |
| Age, Continuous | years | 54.9 (SD 2.8) | 54.8 (SD 2.8) | 54.8 (SD 2.8) |
| Sex: Female, Male: Female | Participants | 6913 | 6972 | 13885 |
| Sex: Female, Male: Male | Participants | 4298 | 4256 | 8554 |
6. Primary Endpoint
The registry lists the primary outcome as Incidence of Confirmed Herpes Zoster (HZ) Cases by Vaccination Group, measured over 2 Years.
| Element | Registry entry |
|---|---|
| Result type | Mean |
| Measure of spread | 95% Confidence Interval |
| Unit | number of HZ cases/1000 person-years |
| Endpoint classification | Continuous Endpoint |
The primary endpoint is the incidence of confirmed herpes zoster (HZ) cases by vaccination group, measured as the number of confirmed HZ cases per 1000 person-years of follow-up following vaccination. The specified timeframe is 2 Years. The registry states that the incidence rate is calculated using confirmed cases relative to person-years of follow-up, and defines vaccine efficacy as the relative reduction in the incidence rate for Zostavax™ compared with placebo in the intent-to-treat population.
An incidence rate is useful when follow-up time matters. It relates observed events to the time participants are followed, so the measure is not merely a count of cases. It can support comparison of groups even when their accumulated person-time differs, subject to the analysis assumptions and the quality of event ascertainment. The registry record does not give the group-specific person-time totals or the underlying confirmed-case counts, so those quantities cannot be described from the posted results.
The endpoint focuses on confirmed clinical cases, rather than antibody response or a broader self-reported symptom measure. Confirmation criteria and adjudication procedures are not reported in the registry record. The group results are reported as incidence rates with 95% confidence intervals; the comparative analysis is reported separately as a point estimate with its own 95% confidence interval and p-value. These measures answer related but different questions: the group rates describe incidence, while the comparative estimate describes the relative contrast under the registry's definition.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The reported incidence rate was 1.994 HZ cases per 1000 person-years in the Zostavax™ group, with a 95% confidence interval from 1.346 to 2.847. In the placebo group, the reported rate was 6.596 per 1000 person-years, with a 95% confidence interval from 5.361 to 8.03. These are group-specific estimates over the primary timeframe of 2 Years. The intervals communicate uncertainty around each rate; they do not show the range of individual participants' outcomes.
The sponsor's reported comparative analysis used the Conditional Exact Method. It gives a point estimate of .698, with a 95% confidence interval from .541 to .806, and p <.001. The registry defines vaccine efficacy as a relative reduction in incidence rate for Zostavax™ compared with placebo. Under that definition, the reported point estimate is the sponsor's estimate of that relative reduction. The confidence interval indicates uncertainty in the comparative estimate; its bounds are not additional observed group rates.
The p-value is evidence against the null hypothesis specified by the analysis, under the method's assumptions. It is not the probability that the null hypothesis is true, and it does not quantify the probability that the observed result arose by chance in a general sense. The registry record does not state the full null hypothesis or all details of the testing procedure, so the p-value should be read in the context of the named analysis and the reported endpoint.
The primary outcome is a rate, and the comparison is reported through a relative measure. Neither should be treated as a direct statement about every participant's experience. The posted figures do not give individual-level outcomes, and they do not describe how outcomes varied across participant characteristics. The group rates also do not provide the total number of cases or total person-time, which are not reported in the registry record.
The registry record identifies the analysis population as intent-to-treat, meaning all randomized participants are grouped according to planned assignment. That is an important feature of the interpretation: the comparison is based on randomized assignment rather than a reclassification according to treatment actually received. The available record does not provide enough detail to assess adherence, crossover, completeness of follow-up, or missing outcome handling.
The reported estimate and uncertainty support a description of the trial's observed comparative result, not a guarantee about outcomes for every person or setting. The record is specific to adults ages 50-59, the study's assigned vaccine and placebo groups, the endpoint definition, and the stated follow-up timeframe. It does not establish results for other populations, alternative schedules, or outcomes not reported in the registry record.
9. Statistical Methods Explained
The registry presents group-specific incidence rates and a separate comparative estimate. These quantities should not be conflated. A rate describes the frequency of confirmed HZ cases relative to accumulated person-time. The sponsor's comparative estimate expresses the relative reduction in the rate for the Zostavax™ group compared with placebo, according to the registry's endpoint definition. The Conditional Exact Method is the method named for that comparison.
What does a confidence interval describe?
A confidence interval expresses uncertainty around an estimate under the statistical procedure used to construct it. The group rates have 95% confidence intervals, as does the reported comparative estimate. The interval is not a statement that a fixed proportion of participants had outcomes within its bounds, nor is it a range containing the true value with a probability assigned after observing the data. In repeated use of a suitable procedure under its assumptions, confidence intervals are designed to cover the target parameter at the stated confidence level.
For the group rates, the intervals are reported separately: 1.346 to 2.847 around the Zostavax™ rate and 5.361 to 8.03 around the placebo rate. The comparative interval, .541 to .806, is for the reported point estimate of .698. Separate group intervals do not by themselves replace the interval for the contrast. Estimating a comparison requires accounting for uncertainty in the relationship between the groups, which is why the sponsor's reported comparative interval is informative in its own right.
What does the p-value contribute?
The reported p-value is p <.001 for the sponsor's comparison. A p-value describes how incompatible the observed data, or data more extreme, are with a specified null model when the model and analysis assumptions hold. It is not an effect-size measure, and it does not measure the clinical importance of a finding. It also does not tell readers the probability that the null hypothesis is true. Interpretation should therefore consider the effect estimate and its confidence interval alongside the p-value.
The registry names a Conditional Exact Method but does not provide enough detail to reconstruct its full implementation. It does not report the exact test statistic, the complete null specification, or any further model details. The named method should therefore be treated as the sponsor's stated analysis, not as an invitation to infer unreported procedures.
Why use an incidence rate?
An incidence rate relates events to time at risk. This is useful when the amount of follow-up can differ among participants, because a raw event count alone does not account for the time during which participants could experience an event. Rates still depend on clear event definitions and sufficiently well-recorded follow-up. The registry reports the endpoint as confirmed cases per 1000 person-years, but the group-specific case counts and person-time totals are not reported in the registry record.
Over-dispersion is a general statistical concern in event-rate analyses. It occurs when observed variability exceeds what a simple model assumes, which can make standard errors too small and confidence intervals too narrow if the model does not account for it. This is a general explanation, not a claim that over-dispersion was present in this trial. The registry record does not report an over-dispersion assessment or enough model detail to determine how this issue was addressed.
What can a recalculation establish?
A simple recalculation from posted summary statistics can sometimes check a contrast under an explicitly stated, unadjusted approach. It cannot reproduce an analysis that depends on unreported event-level data, person-time, stratification, covariate adjustment, or method-specific procedures. For this trial, the registry includes incidence rates and confidence intervals, but the posted information does not support an estimable two-group recalculation for this continuous-endpoint classification. No recalculated comparative estimate is therefore available to place alongside the sponsor's Conditional Exact Method result.
This limitation matters because a simple calculation and the sponsor's stated method need not target precisely the same quantity or use the same assumptions. The observed arm summaries do not contain all the information required to recreate the sponsor's analysis. In the absence of a reproducible recalculation, the sponsor's reported comparison remains the available comparative analysis in the registry record. The record does not report individual-level data or detailed analytic code.
How should planning illustrations be read?
Planning illustrations based on an observed effect are not observed power and are not evidence that the original trial was designed using that effect. The stated illustration assumptions are a two-sided significance level of 0.05, equal allocation between groups, and a normal approximation; the effect to detect is a stated fraction of the observed effect. The registry record does not report that these assumptions were the protocol's original design assumptions or that the trial's enrollment was justified by this calculation.
In general, a sample-size planning calculation describes the approximate enrollment that would be needed under its chosen assumptions to target a specified power for a specified effect. It is conditional on those assumptions and does not predict the result of a future study. An observed-effect-based illustration can be especially sensitive to uncertainty in the observed estimate. It should therefore be distinguished from the trial's enrollment of 22439 and from any actual design justification, which is not reported in the registry record.
10. Analyses Reported by the Sponsor
| Method | Estimate | 95% CI | P-value |
|---|---|---|---|
| Conditional Exact Method | point estimate .698 | .541 to .806 | < 0.001 |
The sponsor's own comparative analysis is reported as a Conditional Exact Method estimate of .698, with a 95% confidence interval from .541 to .806 and p <.001. The registry defines the comparative quantity as the relative reduction in incidence rate for Zostavax™ compared with placebo. This is the available sponsor-reported estimate for the primary comparison.
The posted arm summaries give rates of 1.994 and 6.596 per 1000 person-years, each with a 95% confidence interval. However, the registry record does not contain the information needed to reproduce the sponsor's Conditional Exact Method result from those summaries. A recalculated two-group comparison is not estimable for the continuous-endpoint classification used for the posted arm results. There is consequently no recalculated estimate to compare numerically with the sponsor's result, and no recalculation discrepancy is reported.
When a recalculation differs from a sponsor analysis, the sponsor's own analysis takes precedence as the trial's reported analysis. In this case, the relevant distinction is that the sponsor's result is reported, while the posted summaries do not support a matching recalculation. The absence of a recalculation is not evidence that the sponsor's result is incorrect; it means the necessary information or compatible calculation is not available in the registry record.
11. Multiplicity, Missing Data and Analysis Populations
The registry lists three outcome measures and three analyses. It identifies the incidence of confirmed HZ cases as the primary outcome and lists secondary outcomes concerning varicella-zoster virus antibody response at 6 weeks post vaccination and participants reporting one or more serious adverse experiences during the 42-day postvaccination follow-up period. The registry record does not report a multiplicity adjustment, a hierarchy for testing outcomes, or how the overall chance of false-positive findings across analyses was handled.
Multiplicity is a general issue when several hypotheses are tested. Each test can contribute evidence about its own outcome, but interpreting many results together can raise the chance of at least one apparently unusual result under a collection of null hypotheses. Adjustments or prespecified testing sequences can address this concern, but neither such procedures nor their absence can be inferred beyond what the registry record states. The reported primary p-value should be understood as the value attached to the named primary analysis, with no unreported multiplicity procedure assumed.
The primary population is defined as all participants randomized, analyzed according to the planned treatment assignment. This is the registry's intent-to-treat definition. It does not tell readers how missing outcome data were handled, whether all randomized participants had evaluable follow-up, or how participants with incomplete person-time contributed to the rate analysis. Those details are not reported in the registry record.
Similarly, the record does not report imputation methods, sensitivity analyses for missing data, exclusions from the primary analysis, or analysis populations beyond the stated intent-to-treat definition. It does not report whether an interim analysis was conducted or whether stopping rules were used. These omissions limit assessment of the full analysis process, but they do not alter the figures that the registry does report. The appropriate reading is to distinguish documented design and analysis features from procedures that are not reported in the registry record.
12. Safety Results
The registry reports serious adverse events as affected participants divided by participants at risk.
| Arm | Participants with serious adverse events | Participants at risk | Percentage |
|---|---|---|---|
| Zostavax™ | 243 | 11094 | 2.2% |
| Placebo | 233 | 11116 | 2.1% |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 5% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Zostavax™ | 7228 of 11094 |
| Placebo | 2183 of 11116 |
Most frequent serious adverse event terms
| Event term | Organ system | Zostavax™ | Placebo |
|---|---|---|---|
| Basal cell carcinoma | Neoplasms benign, malignant and unspecified (incl cysts and polyps) | 14 of 11094 | 10 of 11116 |
| Breast cancer | Neoplasms benign, malignant and unspecified (incl cysts and polyps) | 10 of 11094 | 7 of 11116 |
| Chest pain | General disorders | 7 of 11094 | 7 of 11116 |
| Appendicitis | Infections and infestations | 6 of 11094 | 7 of 11116 |
| Non-cardiac chest pain | General disorders | 5 of 11094 | 7 of 11116 |
| Pneumonia | Infections and infestations | 4 of 11094 | 8 of 11116 |
| Myocardial infarction | Cardiac disorders | 4 of 11094 | 5 of 11116 |
| Atrial fibrillation | Cardiac disorders | 2 of 11094 | 6 of 11116 |
| Cellulitis | Infections and infestations | 2 of 11094 | 5 of 11116 |
| Squamous cell carcinoma of skin | Neoplasms benign, malignant and unspecified (incl cysts and polyps) | 3 of 11094 | 4 of 11116 |
Most frequent non-serious adverse event terms
| Event term | Organ system | Zostavax™ | Placebo |
|---|---|---|---|
| Injection site pain | General disorders | 6005 of 11094 | 1025 of 11116 |
| Injection site erythema | General disorders | 5351 of 11094 | 483 of 11116 |
| Injection site swelling | General disorders | 4500 of 11094 | 309 of 11116 |
| Headache | Nervous system disorders | 1041 of 11094 | 917 of 11116 |
| Injection site pruritus | General disorders | 1287 of 11094 | 78 of 11116 |
Serious events with the highest arm-level rate: basal cell carcinoma (0.1%), breast cancer (0.1%), pneumonia (0.1%), chest pain (0.1%), non-cardiac chest pain (0.1%).
The registry's safety information includes counts of participants at risk and counts with serious adverse experiences: 243 of 11094 in the Zostavax™ group and 233 of 11116 in the placebo group. The listed secondary safety outcome is participants reporting one or more serious adverse experiences during the 42-day postvaccination follow-up period. These counts describe the registry's reported safety outcome; they should not be converted into rates or percentages without an appropriate calculation and denominator interpretation.
The record also gives counts for other adverse experiences: 7228 of 11094 in the Zostavax™ group and 2183 of 11116 in the placebo group. These are a separate category from serious adverse experiences. The registry lists several top serious terms, each reported as 0.1%: basal cell carcinoma, breast cancer, pneumonia, chest pain, non-cardiac chest pain, and appendicitis. The term-level percentages do not establish whether an event was caused by vaccination.
Deaths are not reported in the registry record. The posted safety counts do not, by themselves, establish causality, relative risk, or the clinical importance of individual events. They also do not describe timing beyond the stated follow-up for the listed secondary serious-event outcome. Safety interpretation should remain tied to the categories, population, and follow-up period actually reported.
13. What the Result Does, and Does Not, Mean
The primary findings describe confirmed HZ incidence in the two randomized groups and the sponsor's estimate of their relative difference. The reported rates were 1.994 per 1000 person-years for Zostavax™ and 6.596 per 1000 person-years for placebo. The sponsor's Conditional Exact Method estimate was .698, with a 95% confidence interval from .541 to .806 and p <.001. These figures convey the observed result and its statistical uncertainty under the reported analysis.
They do not mean that every participant assigned to one group had the same outcome, nor do they predict an individual's experience. They do not establish results for people outside the study population of adults ages 50-59, or for different treatment schedules and settings. The registry record does not describe enough detail about participant characteristics, adherence, event confirmation, or missing data to support broader subgroup or implementation conclusions.
The reported estimate is defined as a relative reduction in incidence rate, not as the proportion of all participants who avoided shingles. A rate per person-time and a relative comparison are different from a cumulative risk over a specified period. The posted information does not include group-specific case counts or person-time totals, so it cannot support an account of those underlying quantities. It also does not provide a basis for deriving additional absolute effects.
The result is not a complete benefit-risk assessment. The registry reports serious and other adverse-experience counts, but those counts alone do not determine whether an event was caused by the assigned intervention. Further, the listed antibody outcome is distinct from the clinical incidence endpoint. The record does not establish that an antibody response necessarily corresponds to an individual clinical outcome.
Statistically, the confidence interval conveys uncertainty and the p-value relates the data to a null model under the analysis assumptions. Neither conveys all relevant uncertainty about study conduct, generalizability, or measurement. The findings should therefore be read as the trial's reported comparison for its defined endpoint and analysis population, rather than as a universal conclusion about outcomes beyond the registry record.
14. Why This Trial Matters Statistically
This trial illustrates why an outcome's scale matters. The primary endpoint is reported as confirmed HZ cases per 1000 person-years, not simply as a count or a proportion of participants. Rates incorporate time at risk, and their interpretation depends on how events and follow-up are defined. The registry supplies the endpoint definition and timeframe, while leaving group-specific case totals and person-time totals unreported.
It also illustrates the distinction between group estimates and a comparative estimate. The Zostavax™ and placebo rates have separate confidence intervals, while the sponsor reports a Conditional Exact Method comparison with its own confidence interval and p-value. Readers should not infer the uncertainty of the comparison solely from the appearance of the separate group intervals. The contrast is a distinct statistical quantity.
A further lesson concerns reproducibility. Summary statistics can be sufficient for some simple checks, but not necessarily for reconstructing a method-specific analysis. Here, the named sponsor analysis is available, while the posted arm summaries do not support a corresponding recalculation. This makes it important to identify what the registry reports directly and what cannot be independently reproduced from the posted summaries.
Finally, the record identifies an intent-to-treat population but does not give the details needed to assess missing outcome data, interim monitoring, multiplicity handling, or the trial's sample-size justification. Those are meaningful elements of statistical interpretation, not details that can be safely filled in by assumption. The case therefore shows how a clear reading can combine reported estimates with explicit limits on what the record establishes.
15. 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 registry record provides a compact description of the trial but not a full protocol or statistical analysis plan. It identifies the Phase III randomized, double-masked, parallel design, the intent-to-treat population, the primary endpoint, and the sponsor's comparative method. It does not report specific allocation procedures, masking details, event-confirmation procedures, adherence, or follow-up completeness. These omissions restrict assessment of how design and measurement were implemented.
The primary endpoint is expressed as an incidence rate, yet group-specific case counts and person-time totals are not reported in the registry record. As a result, the rate estimates cannot be independently reconstructed from posted event totals, and the Conditional Exact Method comparison cannot be reproduced from the arm summaries. The registry does not report enough detail to evaluate model diagnostics or the handling of potential over-dispersion.
The intent-to-treat definition is stated, but missing-data procedures, exclusions, sensitivity analyses, and other analysis populations are not reported. Multiplicity procedures, interim analyses, and stopping rules are also not reported. These gaps leave uncertainty about analytic choices beyond the named method and displayed result; they should not be taken as evidence that any particular procedure was or was not used.
Generalization is limited by the study population identified as ages 50-59 and by the outcomes and timeframe reported. The registry does not provide subgroup estimates or enough participant-level detail to assess whether the result varied across characteristics. Safety information includes the listed group counts and terms, but deaths are not reported in the registry record, and the reported counts do not establish causation.
Finally, the sample-size planning illustrations are based on the observed effect and stated assumptions. They are not the trial's reported design justification, which is not reported in the registry record, and they should not be interpreted as observed power.
16. Related Tutorials
17. Related Statistical Calculators
18. Sources
- ClinicalTrials.gov: Study to Evaluate the Safety and Effectiveness of Zostavax™ in Subjects 50 - 59 Years of Age (V211-022) — NCT00534248.
- Registry record last updated 2017-04-12; status last verified 2017-03.
- Results first posted 2011-05-02.
- Data retrieved from ClinicalTrials.gov on 2026-11-09.
- Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.
Continue through the Clinical Biostats statistical pathway
Use this trial's endpoint as a starting point for deeper study of effect measures, confidence intervals, and sample-size planning.
19. Record Summary
The registry record describes a completed Phase III randomized, double-masked, parallel-group study sponsored by Merck Sharp & Dohme LLC. It enrolled 22439 participants and compared Zostavax™ with placebo in adults ages 50-59. The recorded study start is 2007-10, and primary completion is 2010-01.
The primary outcome was confirmed HZ incidence per 1000 person-years over 2 Years in the intent-to-treat population. Reported rates were 1.994 for Zostavax™ and 6.596 for placebo. The sponsor's Conditional Exact Method analysis reported a relative-reduction estimate of .698, with a 95% confidence interval from .541 to .806 and p <.001.
Secondary outcomes concern antibody response at 6 weeks post vaccination and serious adverse experiences during the 42-day postvaccination follow-up. The registry reports serious-event counts by group, but deaths are not reported in the registry record. Details of missing-data handling, multiplicity, interim analyses, and the sample-size justification are not reported.