Introduction: While widespread infant vaccination with the upcoming MMR-chickenpox combination vaccine is expected to reduce the incidence of the disease, it could be accompanied by a shift in the age distribution of cases, with an increase in the number of severe cases and congenital chickenpox. To assist in deciding whether to introduce the vaccine into the immunization schedule, a dynamic mathematical model was developed to estimate the impact of vaccination on the epidemiology of the disease. Methods: A deterministic compartmental model was adapted to French data. Epidemiological data were derived from surveillance data or the literature. Different vaccination coverage levels and strategies were tested. A sensitivity analysis was conducted to measure the epidemiological impact of different contact rate matrices and variations in parameters describing vaccine efficacy. Results: The model confirms the reduction in the incidence of chickenpox through widespread vaccination of infants, but also a shift in the age of cases, with—for vaccination coverage levels below at least 80% in the baseline analysis—an increase in morbidity among adults and thus pregnant women. Nevertheless, the total number of chickenpox-related deaths and hospitalizations is expected to be lower than those observed before vaccination. The number of shingles cases is expected to increase for about thirty years before falling below current levels. The model is highly sensitive to the choice of contact matrices and vaccine-related parameters. Conclusion: widespread vaccination of infants would lead to a decrease in the incidence of chickenpox but also to an increase in cases among adults, the actual magnitude of which is difficult to determine due to uncertainty regarding the values of certain key model parameters. (R.A.)