aa‐Henry 2018.

Study characteristics
Methods	RCT ‐ Phase A, observer‐blind, controlled study conducted in Czech Republic, Greece, Italy, Lithuania, Norway, Poland, Romania, Russian Federation, Slovakia, and Sweden between 2009 and 2015. Phase B, the study remained observer‐blind for all groups with the exception of the MMR+V group in countries where the national vaccination schedules included a second dose of MMR vaccination at 4 to 8 years of age (Italy, Lithuania, Romania, Russian Federation, Sweden). Phase B follow‐up of an initial multicentre study (NCT00226499) ‐ evaluation of the 10‐year efficacy of 2 doses of the combined MMRV vaccine and 1 dose of the live attenuated varicella vaccine (V) versus an MMR control group for the prevention of clinical varicella disease. This study presents results at 6 years' follow‐up of the study aa‐Prymula 2014.
Participants	Healthy children aged 12 to 22 months. N = 5803 children enrolled and vaccinated. Total vaccinated cohort (TVC), in phase A, N = 4580 were included in the TVC in phase B, N = 3829 completed the study up to Year 6; N = 5289 and N = 3791 were included in the According To Protocol (ATP) cohort for efficacy in phase A + B and phase B, respectively.
Interventions	3 treatment groups: Phase A 2 doses of MMRV (Priorix‐Tetra, GSK) at Day 0 and Day 42 (MMRV group) 1 dose of MMR (Priorix, GSK) at Day 0 and 1 dose of monovalent varicella vaccine (Varilrix, GSK) at Day 42 (MMR+V group) 2 doses of MMR (Priorix, GSK) vaccine (control) at Day 0 and Day 42 (MMR group) For phase B, the study remained observer‐blind for all groups with the exception of the MMR+V group in countries where the national vaccination schedules included a second dose of MMR vaccination at 4 to 8 years of age (Italy, Lithuania, Romania, Russian Federation, Sweden). Independent data monitoring committee members also remained blinded to the study treatment group when assessing varicella cases.
Outcomes	Number (percentage) of children with reported contact with varicella or zoster disease, or both
Funding Source	Pharmaceutical Industry
Notes	Conclusion: 2 doses of the MMRV vaccine and 1 dose of the varicella vaccine remain efficacious through 6 years postvaccination
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Adequate ‐ computer‐generated randomisation list ‐ randomised (3:3:1) ‐ block size 7
Allocation concealment (selection bias)	Low risk	Adequate ‐ centralised randomisation
Blinding (performance bias and detection bias) All outcomes	Low risk	Adequate ‐ participants and their parents or guardians, individuals involved in assessment of any outcome, and sponsor staff involved in review or analysis of data were masked to treatment assignment.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Adequate ‐ < 10%. The exclusions are well documented, and it seems unlikely that they could have affected the results.
Selective reporting (reporting bias)	Low risk	Adequate ‐ all outcomes are reported
Summary Risk of Bias assessment	Low risk	Plausible bias is unlikely to have seriously altered the results.