Background: In recent years, the number of varicella cases in adults has significantly increased in Beijing, However, the effect of the vaccination on varicella-related characteristics among adults has not been studied.Methods and Results: Using data from the Infectious Disease Reporting System and the Immunization Information System, we compared the epidemiology and disease severity in breakthrough and unvaccinated varicella cases in adolescents and adults (≥ 15 year-old) from 2008 to 2011 in Beijings Fengtai district, China.The results showed that the age (P=0.003), contact history (90% versus 73%, P=0.019) and outbreak cases (10% versus 1%,P<0.0001) were significantly differently distributed between the two groups and that both the incidence of moderate-to-severe cases (26% versus 45%, P=0.035, OR=0.446) and varicella-associated fever (49% versus 66%, P=0.068, OR=0.534) were either significantly lower or trended to be lower in the breakthrough group than in the unvaccinated group.Additionally, vaccine effectiveness against moderate-to-severe cases of varicella was 55.4%.Conclusions: Altogether,these results indicate that vaccination against varicella among adolescents and adults affected the epidemiology and attenuated the disease severity of the cases.The Results from this study will provide useful information for the prevention of varicella in adolescents and adults.