OBJECTIVES:: Varicella vaccines have been available in Mexico since 2000. Use was initially restricted to private practices and children undergoing bone marrow transplantation, but in recent years, coverage among children 1 year of age has increased through selected insurers and/or states offering coverage. The objective of this study was to evaluate vaccine characteristics and coverage levels that might lead to substantial age-shifts in varicella burden in Mexico. METHODS:: A dynamic transmission model of varicella infection calibrated to local data was employed. Vaccination coverage levels of one year olds between 5% and 95% were considered together with the properties of three different hypothetical vaccines (Strong/Moderate/Low), defined by initial effectiveness (95%/75%/50%), average duration of protection (25/5/1 years), and relative infectiousness of vaccinees post waning (0.25, 0.5, 0.75). RESULTS:: While all vaccines and coverage levels predicted reduced overall varicella incidence, some combinations of vaccine effectiveness and coverage rates led to increases in age-specific incidence rates, shifting towards older onset of disease. Among those aged 25+, within 20-40 years of the start of the vaccination programme, varicella incidence rates will be higher than pre-vaccine incidence rates for all coverage levels for the Low vaccine; for any coverage <90% for the Moderate vaccine; and for coverage <75% for the Strong vaccine. The largest increases are predicted at coverage levels of 30-60% (Strong), 30-80% (Moderate), and 60-100% (Low). A similar pattern was predicted within 40-60 years among those aged 65+, with the most significant increase for the Low vaccine. CONCLUSIONS:: Careful monitoring of evolving private sector and sub-national coverage in Mexico is recommended to avert potential shifts in the age-distribution of cases to older age groups where disease is more severe. The impact of current policies may not be observed for 10-50 years. Vaccine characteristics play a significant role in potentially increasing future varicella disease burden in older age groups.