In this open, randomized, comparative study (105908/NCT00353288), 458 age-stratified children (15 months-2 years and 2-6 years) previously primed with MMR received one dose of either a combined MMRV vaccine (Priorix-Tetra, MMRV group) or concomitant MMR and varicella vaccines (Priorix and Varilrix, MMR+V group), followed 42-56 days later by another dose of varicella vaccine (Varilrix) in both groups. Post-vaccination measles, mumps and rubella seropositivity rates and antibody geometric mean titers (GMTs) were high (99.5% for anti-measles and 100% for anti-mumps and anti-rubella) in both vaccine groups. In the two age strata, varicella seroconversion rates were, post-dose 1: > or =97.6% (MMRV), > or =96.6% (MMR+V) and, post-dose 2: 100% in both groups. Post-dose 2, anti-varicella GMTs increased respectively 14.1- and 12.6-fold (MMRV), and 9.8- and 13.1-fold (MMR+V). Both vaccine regimens were well-tolerated. Post-dose 1, the incidence of any solicited local symptom during the 4-days follow-up was < or =28.2% (MMRV) and < or =19.8% (MMR+V) and the incidence of fever >39.5 degrees C (rectal temperature) within 15 days was < or =2.8% (MMRV) and < or =2.6% (MMR+V). This MMRV vaccine appears an immunogenic and safe substitute for a second dose of MMR vaccine in young children. The increase in anti-varicella antibodies observed after a second dose of varicella vaccine supports a two-dose schedule for varicella-containing vaccine.