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 Comparison of GSK Measles-mumps-rubella-varicella (MMRV) Vaccine Versus PriorixTM (NCT00969436), a randomized phase 3 study. The primary outcome is Number of Subjects Seroconverted for Measles, Mumps, Rubella and Varicella Antibodies.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT00969436 |
| Phase | Phase 3 |
| Condition | Varicella, Rubella, Mumps |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | None (open label) |
| Enrollment | 450 |
| Arms in the primary outcome | n/a |
| Lead sponsor | GlaxoSmithKline |
| Results posted | Yes |
2. Clinical Question
Population
Healthy children in a measles-endemic setting such as India. The primary immunogenicity analysis used the According-To-Protocol cohort, defined as eligible subjects with available pre-vaccination and post-vaccination serology for antibodies against at least one antigen.
Intervention
One regimen used the GSK investigational MMRV vaccine at Day 0 and Month 6. The registry’s arm description calls this the Priorix-Tetra Group and describes both doses as subcutaneous injections in the left anterolateral thigh.
Comparator
The control regimen used Priorix at Day 0, followed at Month 6 by Priorix co-administered with Varilrix. Both were administered subcutaneously, in the left and right anterolateral thigh at Month 6.
Primary question
The trial aimed to assess whether the investigational MMRV regimen, and an alternative regimen of Priorix followed by MMRV, were non-inferior to the control regimen. The primary measure was the number of subjects seroconverted for antibodies against measles, mumps, rubella and varicella, assessed 42 - 56 days after the second vaccination dose at week 30.
The registry describes three groups: two doses of the investigational MMRV vaccine; Priorix followed by the investigational MMRV vaccine; and Priorix followed by Priorix co-administered with Varilrix. Its official title also describes the vaccination courses in terms of administration at 9 and 15 months of age. The brief summary places the study in a measles-endemic environment such as India.
The clinical question is about immune response after the vaccination courses, not a direct measure of clinical disease prevention. Seroconversion records whether antibodies reach the specified cut-off in subjects who were seronegative before vaccination. The registry lists the intended non-inferiority comparisons, but the non-inferiority margin and primary outcome results are not reported in the registry record. Therefore, the record does not allow a reader to determine whether either regimen met the intended criterion.
3. Trial Design
This was a phase IIIb, randomized, open, multicentre, parallel-group study. The registry lists enrollment as 450 and status as completed. GlaxoSmithKline is named as the sponsor. The recorded start date is 2009-11-09 and the primary completion date is 2011-02-21.
Participants were assigned to one of three two-dose courses. The Priorix-Tetra Group received two doses of Priorix-Tetra, at Day 0 and Month 6. The Priorix/Priorix-Tetra Group received Priorix at Day 0 and Priorix-Tetra at Month 6. The Control Group received Priorix at Day 0 and Priorix co-administered with Varilrix at Month 6. The arm descriptions specify subcutaneous administration. The registry uses different vaccine labels across its official title, intervention list and arm descriptions; the relationships between those labels are not clarified further in the registry record.
The official title describes vaccination at 9 and 15 months of age, while the arm descriptions express timing as Day 0 and Month 6. It describes the main objective as establishing non-inferiority of the investigational regimen versus the control and also evaluating non-inferiority of the alternative regimen. The trial was unmasked, so participants and study staff were not blinded according to the registry’s masking field.
The primary immunogenicity analysis was defined for the According-To-Protocol cohort. That cohort included eligible subjects with pre-vaccination and post-vaccination serology available for antibodies against at least one antigen. The record does not report the randomization procedure, allocation concealment, the non-inferiority margin, or further details of the statistical plan. The planned and analyzed group sizes for the primary immunogenicity endpoint 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.
Before assignment: During the screening the following steps occurred: check for inclusion/exclusion criteria, contraindications/precautions, medical history of the subjects and signing informed consent forms.
Overall Study
| Stage | Priorix-Tetra Group | Priorix/ Priorix-Tetra Group | Control Group |
|---|---|---|---|
| STARTED | 180 | 180 | 90 |
| COMPLETED | 155 | 159 | 79 |
| NOT COMPLETED | 25 | 21 | 11 |
Reasons for not completing this period:
| Reason | Priorix-Tetra Group | Priorix/ Priorix-Tetra Group | Control Group |
|---|---|---|---|
| Protocol Violation | 1 | 3 | 0 |
| Migrated/moved from study area | 12 | 10 | 2 |
| Father - serious health problem | 0 | 0 | 1 |
| Parents personal problem | 0 | 0 | 1 |
| Subject eliminated (other vaccine) | 1 | 0 | 0 |
| Withdrawal by Subject | 3 | 0 | 2 |
| Lost to Follow-up | 8 | 8 | 5 |
Analysis population for the primary outcome, as defined in the registry: The analysis was performed on the According-To-Protocol (ATP) cohort for immunogenicity, which included all eligible subjects for whom pre-vaccination and post-vaccination serology results were available for antibodies against at least one antigen.
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 | Priorix-Tetra Group | Priorix/ Priorix-Tetra Group | Control Group | Total |
|---|---|---|---|---|---|
| Participants analysed | 180 | 180 | 90 | 450 | |
| Age, Continuous | Months | 9 (SD 0) | 9 (SD 0.11) | 9 (SD 0) | 9 (SD 0.07) |
| Sex: Female, Male: Female | Participants | 79 | 89 | 49 | 217 |
| Sex: Female, Male: Male | Participants | 101 | 91 | 41 | 233 |
| Race/Ethnicity, Customized: Asian - central/ south Asian heritage | Participants | 177 | 175 | 88 | 440 |
| Race/Ethnicity, Customized: Asian - south east Asian heritage | Participants | 2 | 5 | 2 | 9 |
| Race/Ethnicity, Customized: American Indian or Alaskan native | Participants | 1 | 0 | 0 | 1 |
6. Primary Endpoint
The registry lists the primary outcome as Number of Subjects Seroconverted for Measles, Mumps, Rubella and Varicella Antibodies, measured over At 42 - 56 days after the second vaccination dose at week 30.
| Element | Registry entry |
|---|---|
| Result type | Count Of Participants |
| Measure of spread | not applicable |
| Unit | Participants |
| Endpoint classification | Binary Endpoint |
The primary endpoint is the number of subjects seroconverted for measles, mumps, rubella and varicella antibodies. Seroconversion was defined as the appearance of antibodies at or above the specified cut-off in the serum of subjects who were seronegative before vaccination. The recorded cut-offs were 150 milli-international units per milliliter for measles, 231 units per milliliter for mumps, 4 international units per milliliter for rubella, and a 1:4 dilution for varicella IgG.
The measure is assessed 42 - 56 days after the second vaccination dose at week 30. Using a threshold-based antibody response allows the study to describe the proportion or count of initially seronegative subjects who reached a defined serological level after vaccination. That is an immunogenicity measure; it is not itself a count of infections or a direct measure of clinical protection.
The registry identifies an endpoint count, but does not report its results by group. It also does not report a single combined summary or a non-inferiority margin for interpreting the endpoint. Because the primary measure spans four antigens, results for each antigen and the rules for judging the overall non-inferiority objective would be important for interpreting the study. Those results and rules are not reported in the registry record.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record sets out a randomized comparison of three vaccination regimens and names seroconversion for four antigens as the primary outcome. It does not report the primary endpoint counts, group-specific seroconversion results, effect estimates, confidence intervals or p-values. The record therefore does not show the size or precision of any difference between regimens, and it does not establish whether the stated non-inferiority objective was met.
Non-inferiority is a particular statistical claim: it asks whether an intervention is no worse than a comparator by more than a prespecified margin. General explanation: the estimated difference must be sufficiently precise relative to that margin; merely observing similar-looking responses would not establish non-inferiority. The margin and the primary analysis results are not reported in the registry record, so the criterion cannot be assessed from this record.
The primary outcome combines a count-based description with several antigen-specific responses. Results for measles, mumps, rubella and varicella would need to be read separately or under a clearly defined combined decision rule. No such numerical results or rule are reported. The registry also lists secondary immunogenicity outcomes, including seroconverted subjects and antibody concentrations, alongside safety outcomes. Their numerical results are not reported in the registry record.
The cohort definition matters to interpretation. The primary analysis was specified for eligible subjects with available pre- and post-vaccination serology for at least one antigen. This is an analysis population based on protocol eligibility and available measurements; it is not necessarily identical to every randomized participant. The registry does not report the group-specific analysis population sizes or the handling of participants without the required measurements.
The record includes safety counts by group, but these do not fill the gap in the primary immunogenicity results. They describe participants recorded with serious adverse events and other adverse events in the registry’s safety fields. The record does not supply enough context to infer comparative safety beyond those posted counts. In particular, the numerical primary endpoint, its precision and the decision rule for non-inferiority are not reported in the registry record.
Thus, the appropriate statistical reading is descriptive: the trial’s design and intended question are documented, but its main comparative result cannot be reconstructed from the registry information. No recalculated effect estimate is presented, and no conclusion about the relative immunogenicity of the regimens follows from the design description alone.
9. Statistical Methods Explained
What does randomization contribute?
General explanation: random assignment is used to make treatment groups comparable, on average, with respect to measured and unmeasured characteristics at the point of assignment. It supports a fair comparison when the assigned groups are analyzed appropriately. The registry identifies the study as randomized and parallel-group, but does not report the sequence-generation method, allocation concealment, or group-specific participant flow. Those details are not reported in the registry record.
The study was open, meaning the registry records no masking. General explanation: lack of masking can affect behavior, reporting and assessment, depending on the outcome. Antibody measurements are laboratory measures, but the registry record does not describe laboratory masking or other procedures that might limit assessment bias. It is not possible to determine those details from the record.
How should a non-inferiority objective be evaluated?
General explanation: a non-inferiority study tests whether the effect of an intervention is not unacceptably worse than that of a comparator, according to a margin set before the results are examined. The estimated contrast and its confidence interval are considered relative to that margin. A confidence interval expresses the uncertainty around an estimate; a narrow interval indicates greater precision than a wide interval. The registry states the non-inferiority objective but does not report the margin, the contrast definition, confidence intervals or the decision rule. Consequently, the statistical criterion cannot be checked.
Non-inferiority analyses often require particular attention to departures from the assigned regimen and missing outcome data. General explanation: such departures can make groups more alike and can complicate interpretation, so the analysis population and sensitivity analyses are important. Here, the registry defines the primary analysis cohort as eligible subjects with pre-vaccination and post-vaccination serology available for at least one antigen. It does not report an intention-to-treat analysis, sensitivity analyses, exclusions by group or reasons for missing data.
What does the endpoint count represent?
The endpoint is a count of subjects meeting an antibody threshold after vaccination, among those seronegative before vaccination. Each of the four antigens has a stated cut-off, and the endpoint timing is 42 - 56 days after the second vaccination dose at week 30. General explanation: binary outcomes such as meeting or not meeting a threshold can be summarized as counts and proportions. Comparing such outcomes requires both the group counts and the denominators used for analysis. The registry record does not report the primary counts or denominators by group.
Because the endpoint covers multiple antigens, interpretation depends on how antigen-specific results are presented and how the study’s overall objective was to be judged. A combined endpoint, separate tests or a prespecified rule could address different questions. The registry record does not report such a rule or the primary results. It would therefore be inappropriate to treat the four responses as one established finding or to infer a result from the stated objective.
What can the planning information establish?
General explanation: a sample-size calculation is a planning exercise based on assumptions about the effect to detect, variability or event frequency, significance level and desired power. A planning illustration based on an observed effect is not the same as the trial’s original design justification, and it is not observed power. The record describes planning assumptions using a two-sided significance level of 0.05, equal allocation between two arms and a normal approximation, with the effect to detect expressed as a fraction of the observed effect. It also states that non-time-to-event planning values are participants per arm.
The registry does not report the trial’s own sample-size justification or the assumed non-inferiority margin. The primary outcome is not reduced in the record to a single comparison for planning purposes, because it has several categories or time points. No sample-size illustration should therefore be read as evidence that the trial had a particular level of power for its primary non-inferiority objective.
How should uncertainty and multiple outcomes be considered?
General explanation: confidence intervals help distinguish a precise estimate from one that remains uncertain, while p-values address compatibility with a specified null model under statistical assumptions. Neither measure alone establishes clinical importance, and neither can substitute for a prespecified non-inferiority margin. No primary confidence intervals or p-values are reported in the registry record.
Multiple antigens and additional outcomes create multiple opportunities for comparisons. General explanation: when many hypotheses are tested, some apparently notable results can arise by chance, so a statistical plan may define primary comparisons, testing order or adjustment procedures. The registry lists secondary antibody, symptom and adverse-event outcomes, but multiplicity procedures are not reported in the registry record. Without those procedures and the numerical results, the evidence across outcomes cannot be statistically synthesized from the registry entry alone.
10. Multiplicity, Missing Data and Analysis Populations
The primary outcome covers seroconversion against four antigens, and the registry also lists secondary immunogenicity and safety outcomes. General explanation: evaluating many outcomes or comparisons raises multiplicity concerns because the chance of at least one apparently notable result can increase as the number of tests grows. A prespecified hierarchy, adjustment method or clearly defined primary decision rule can help make the interpretation consistent. Such procedures are not reported in the registry record.
The record states that the primary immunogenicity analysis used the According-To-Protocol cohort. It included eligible subjects with pre-vaccination and post-vaccination serology available for antibodies against at least one antigen. This definition does not describe what happened when a subject lacked a measurement for one or more antigens, nor does it give group-specific exclusions or analysis denominators. Those details are not reported in the registry record.
The record does not describe an intention-to-treat analysis, imputation, sensitivity analyses or the assumptions used to handle missing serology. General explanation: excluding participants without observed measurements can affect a comparison if missingness is related to group assignment or response. Sensitivity analyses can assess how conclusions change under different assumptions, but whether they were conducted is not reported in the registry record.
The registry names the intended non-inferiority comparisons, but does not report the margin, formal testing sequence or multiplicity adjustment. Primary results, including group counts, effect estimates and uncertainty intervals, are also not reported in the registry record. Without these elements, readers cannot verify the non-inferiority decision or assess how the several antigen-specific and secondary outcomes were handled as a family of analyses.
11. 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 |
|---|---|---|---|
| Priorix-Tetra Group | 7 | 180 | 3.9% |
| Priorix/ Priorix-Tetra Group | 6 | 180 | 3.3% |
| Control Group | 0 | 90 | 0.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Priorix-Tetra Group | 0 of 180 |
| Priorix/ Priorix-Tetra Group | 0 of 180 |
| Control Group | 0 of 90 |
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 |
|---|---|
| Priorix-Tetra Group | 114 of 180 |
| Priorix/ Priorix-Tetra Group | 116 of 180 |
| Control Group | 55 of 90 |
Most frequent serious adverse event terms
| Event term | Organ system | Priorix-Tetra Group | Priorix/ Priorix-Tetra Group | Control Group |
|---|---|---|---|---|
| Gastroenteritis | Infections and infestations | 2 of 180 | 3 of 180 | 0 of 90 |
| Lower respiratory tract infection | Infections and infestations | 2 of 180 | 1 of 180 | 0 of 90 |
| Viral infection | Infections and infestations | 1 of 180 | 1 of 180 | 0 of 90 |
| Pneumonitis | Respiratory, thoracic and mediastinal disorders | 1 of 180 | 0 of 180 | 0 of 90 |
| Upper respiratory tract inflammation | Respiratory, thoracic and mediastinal disorders | 0 of 180 | 1 of 180 | 0 of 90 |
| Wheezing | Respiratory, thoracic and mediastinal disorders | 1 of 180 | 0 of 180 | 0 of 90 |
| Febrile convulsion | Nervous system disorders | 0 of 180 | 1 of 180 | 0 of 90 |
| Pyrexia | General disorders | 1 of 180 | 0 of 180 | 0 of 90 |
| Dehydration | Metabolism and nutrition disorders | 0 of 180 | 1 of 180 | 0 of 90 |
| Bronchiolitis | Infections and infestations | 0 of 180 | 1 of 180 | 0 of 90 |
Most frequent non-serious adverse event terms
| Event term | Organ system | Priorix-Tetra Group | Priorix/ Priorix-Tetra Group | Control Group |
|---|---|---|---|---|
| Fever; Dose 1 | General disorders | 76 of 174 | 70 of 172 | 27 of 83 |
| Fever; Dose 2 | General disorders | 41 of 155 | 37 of 159 | 22 of 79 |
| Pain; Dose 1 | General disorders | 20 of 180 | 12 of 180 | 9 of 90 |
| Redness; Dose 1 | General disorders | 15 of 174 | 8 of 172 | 3 of 84 |
| Cough; Dose 1 | Respiratory, thoracic and mediastinal disorders | 6 of 180 | 10 of 180 | 6 of 90 |
| Pain; Dose 2 | General disorders | 9 of 155 | 10 of 159 | 3 of 79 |
| Rhinitis; Dose 1 | Infections and infestations | 7 of 180 | 9 of 180 | 6 of 90 |
| Nasopharyngitis; Dose 1 | Infections and infestations | 4 of 180 | 8 of 180 | 6 of 90 |
| Upper respiratory tract infection; Dose 1 | Infections and infestations | 10 of 180 | 7 of 180 | 1 of 90 |
| Rhinitis; Dose 2 | Infections and infestations | 6 of 180 | 7 of 180 | 5 of 90 |
Serious events with the highest arm-level rate: gastroenteritis (1.7%), lower respiratory tract infection (1.1%), pneumonitis (0.6%), upper respiratory tract inflammation (0.6%), wheezing (0.6%).
The registry’s safety fields list serious adverse events for the Priorix-Tetra Group as 7 among 180 at risk, for the Priorix/Priorix-Tetra Group as 6 among 180 at risk, and for the Control Group as 0 among 90 at risk. Deaths are listed as 0 in each group. These are the recorded group figures; they do not by themselves establish that the regimens differ in safety.
The registry also lists top serious-event terms with percentages: Gastroenteritis, 1.7%; Lower respiratory tract infection, 1.1%; Pneumonitis, 0.6%; Upper respiratory tract inflammation, 0.6%; Wheezing, 0.6%; and Febrile convulsion, 0.6%. The record does not specify a group for these term percentages in the listed data, so they should not be attributed to an individual arm.
General explanation: safety counts are most informative when their definitions, observation periods, event severity, relatedness assessments and denominators are clear. The registry lists other adverse-event counts as well, but the timing and detailed assessment rules are not reported in the registry record. A zero recorded count is a description of the posted data, not proof that an event is impossible or that no risk exists.
12. What the Result Does, and Does Not, Mean
The record establishes that a randomized, open, parallel-group study was conducted to compare three vaccination courses in healthy children. It specifies a primary immunogenicity endpoint based on seroconversion for measles, mumps, rubella and varicella antibodies, and describes the timing and antibody cut-offs. It also identifies the intended non-inferiority comparisons and the primary analysis cohort.
However, the registry record does not report the primary outcome results. It contains no group-specific seroconversion counts, comparative estimates, confidence intervals or p-values for that endpoint. It also does not state the non-inferiority margin or decision rule. The record therefore cannot show whether either non-control regimen met the trial’s non-inferiority objective, nor how precisely any comparative effect was estimated.
The endpoint is an antibody response measure rather than a direct count of disease cases. General explanation: immunogenicity results can describe immune responses under a defined assay threshold, while disease prevention is a different outcome. The registry entry does not provide clinical disease results that would connect these antibody measures to disease occurrence in this study.
The posted safety figures describe recorded serious adverse events and deaths by group, alongside selected serious-event terms. They are useful as descriptive registry data but do not, without fuller context and a comparative analysis, establish a causal difference in safety. The record does not report detailed observation periods or the statistical methods for comparing safety outcomes.
The appropriate conclusion is limited to what is documented: the trial’s design and intended question are clear enough to describe, but its primary comparative finding is not reported in the registry record. Neither benefit nor lack of benefit, and neither superiority nor non-inferiority, can be inferred from the study objective or the safety counts alone.
13. Why This Trial Matters Statistically
This study illustrates how a clinical question can be stated more clearly than its result. The registry identifies three vaccination courses, a randomized parallel design and a non-inferiority objective. It also defines an antibody-based primary endpoint across four antigens. These details help readers understand what the investigators intended to compare, but they do not answer whether the comparison met its statistical objective.
Non-inferiority questions depend on both the estimated difference and a prespecified margin. General explanation: a result that appears close to the comparator is not enough; the uncertainty around the difference must be considered against the margin. In this record, neither the margin nor the primary estimates and their precision are reported. This makes the distinction between a design objective and an evidentiary conclusion especially important.
The trial also highlights the role of analysis populations. Its primary analysis uses an According-To-Protocol cohort requiring available serology for at least one antigen. That population definition is relevant to interpretation, particularly for a non-inferiority objective, but group-specific inclusion, exclusion and missing-data details are not reported in the registry record.
Finally, a multi-antigen endpoint and numerous secondary outcomes make clear why a statistical plan matters. General explanation: prespecified handling of multiple comparisons helps readers understand which result carries the main evidentiary weight and how secondary findings should be interpreted. Those procedures are not reported in the registry record. The entry is therefore informative about the design, endpoint definition and some safety counts, while remaining insufficient to assess the primary comparative conclusion.
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 statistical interpretation is that primary outcome results are not reported in the registry record. Group-specific seroconversion counts, denominators, effect estimates and uncertainty intervals are unavailable, so the magnitude and precision of the comparison cannot be assessed.
The record states a non-inferiority objective but does not report the non-inferiority margin, formal decision rule or statistical analysis plan. It also does not report whether the analyses followed a prespecified hierarchy or how multiple antigen-specific and secondary comparisons were handled. The stated objective alone cannot establish that non-inferiority was demonstrated.
The primary population is described as an According-To-Protocol immunogenicity cohort with available pre- and post-vaccination serology for at least one antigen. The record does not provide group-specific analysis sizes, participant flow, reasons for missing serology, or an intention-to-treat or sensitivity analysis. These omissions limit assessment of selection and missing-data effects.
The trial was open, and the registry does not describe laboratory masking or other protections against assessment bias. It also does not report the randomization procedure or allocation concealment. The arm and intervention labels vary across the registry’s descriptions, and the relationship between the different vaccine names is not clarified further in the registry record.
For safety, the record gives group counts and selected serious-event terms, but detailed observation periods, event definitions and comparative analyses are not reported in the registry record. These limits mean that the posted safety figures should be treated as descriptive rather than as a complete comparative assessment.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Comparison of GSK Measles-mumps-rubella-varicella (MMRV) Vaccine Versus PriorixTM — NCT00969436.
- Registry record last updated 2018-06-08; status last verified 2017-05.
- Results first posted 2017-09-25.
- 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.
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18. Record Summary
The registry describes a completed phase IIIb, randomized, open, multicentre, parallel-group study sponsored by GlaxoSmithKline, with enrollment listed as 450. It compared three two-dose vaccination regimens in healthy children: two doses of Priorix-Tetra; Priorix followed by Priorix-Tetra; and Priorix followed by Priorix co-administered with Varilrix.
The primary endpoint was the number of subjects seroconverted for measles, mumps, rubella and varicella antibodies, assessed 42 - 56 days after the second vaccination dose at week 30. The primary immunogenicity analysis used an According-To-Protocol cohort. The registry states a non-inferiority objective but does not report the margin or the primary outcome results. It lists serious adverse events and deaths by group, as well as selected serious-event terms. The recorded start date is 2009-11-09, and the primary completion date is 2011-02-21.