Background - The upcoming availability of a combined vaccine against measles, mumps, rubella, and chickenpox has reignited the debate over widespread chickenpox vaccination for infants. In France, the number of chickenpox cases is estimated at approximately 700,000 per year, leading to about 3,500 hospitalizations and 15–25 deaths, with the majority of deaths occurring after age 15. Routine vaccination of infants is expected to reduce the incidence of the disease but could be accompanied by a shift in the age of cases, with an increase in the number of severe cases and congenital chickenpox. To aid decision-making, a dynamic mathematical model was developed to estimate the impact of vaccination on the epidemiology of chickenpox and shingles. 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 chickenpox incidence through widespread infant vaccination. Regardless of vaccination coverage or strategy, vaccination is also expected to shift the age of cases; in the base-case analysis, with vaccination coverage below at least 80%, there would be an increase in morbidity among adults and 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 30 years before falling below the levels observed without vaccination. The model is highly sensitive to the choice of contact matrices and to the parameters describing the efficacy of the vaccine used. 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.