OBJECTIVES: To assess the impact of mass vaccination with Priorix-TetraTM (GlaxoSmithKline Biologicals’ MMRV; measles, mumps, rubella, varicella) vaccine versus PriorixTM (GlaxoSmithKline Biologicals’ MMR; measles, mumps, rubella) vaccine on the epidemiology of varicella and zoster. Sustained high coverage with MMRV is possible by replacing MMR. Vaccination can cause an age shift in varicella incidence, and could conceivably increase zoster incidence by removing the trigger for internal boosting of immunity to zoster. METHODS: A dynamic transmission model was developed, accounting for the natural history of varicella and zoster, virus transmission, interactions between varicella and zoster (boosting effects), and age-specific contact rates. The model used peer-reviewed French data. Scenarios were run to evaluate uncertainty in contact patterns within and between age groups. RESULTS: Following the introduction of MMRV, varicella incidence was significantly reduced from 12,571 to 4,859/million person-years at the post-vaccination equilibrium (after around 30 years). All evaluated contact patterns predicted large decreases in disease incidence. Zoster incidence increased slightly in the first 20 years post-vaccination (e.g. 1860 to 1918/million-person-years in people aged >50 years). This then declined as the vaccinated cohort aged, due to the assumed lower viral reactivation rate with the vaccine. Before vaccination, the highest incidence of varicella was in the 2-4 year olds, but this shifted to the 5-11 year age group (pre-vaccination incidence 2373 versus 3535/million person-years after MMRV).  Neither the short term increase in zoster cases nor the age shift to 5-11 year olds were projected to have a significant impact on the burden of the disease. By 80 years post-vaccination, the incidence of zoster had decreased from 3242 to 1326/million person-years and was still decreasing as the vaccinated cohort aged. CONCLUSIONS: Replacement of PriorixTM with Priorix-TetraTM allows sustained mass vaccination against varicella which is predicted to significantly reduce varicella, and eventually zoster, incidence and disease burden.