Objective To evaluate the vaccine efficacy（VE） of different doses of varicella vaccine（Var V） in vari-cella aggregated outbreaks in schools and kindergartens. Methods A total of 816 students（26 students who had varicella before 2015 were excluded） from 21 classes in 10 schools/kindergartens in Yantai where varicella aggre-gation outbreaks occurred in 2015—2016 were selected as study subjects

and a retrospective cohort study was used to evaluate the VE of Var Vof different doses. Results Among the study subjects

the prevalence of vari-cella was 2.11%

11.53% and 23.26% in the 2-dose

1-dose and non-vaccinated groups

respectively

with sta-tistically significant differences（P<0.05）. The VE of 2-dose Var V was 90.93%

and that of 1-dose Var V was 50.43%. Among the subjects immunized with 1-dose Var V

the VE of the group with <3 years of vaccination was 85.68%

and that of the group with ≥3 years of vaccination was only 46.82%

with no statistically signifi-cant difference（P>0.05）. Among the subjects immunized with 2-dose Var V

the VE of the group with <3 years of vaccination was 92.30%

and that of the group with ≥3 years of vaccination was 89.68%

with no sta-tistically significant difference（P>0.05）. Among the study subjects immunized with 1 dose of Var V

the VE was 48.07% in the group with an age at vaccination onset of 1 ～<3 years and 57.52% in the group with an age at vaccination onset of ≥3 years

and the difference was not statistically significant（P>0.05）. Among the stud-y subjects immunized with 2 doses of VarV

the VE was 90.63% in the group with an age at vaccination onset of 1～<3 years and 100.00% in the group with an age at vaccination onset of ≥3 years

and the difference was not statistically significant（P>0.05）.The difference in the distribution of case types among the study subjects with different vaccination doses was statistically significant（P<0.05）

with 3 mild cases（60.00%） occurring in the study subjects with 2 doses of Var Vimmunization

which was higher than in the study subjects with no vaccina-tion and 1 dose of Var Vimmunization. There were 49（81.67%） and 2（3.33%） medium and heavy cases in the unvaccinated study subjects

more than those in the 1-dose Var Vimmunized-and 2-dose Var Vimmunized-study subjects

respectively. Conclusion Immunization with 2-doze vaccine has better durability and is more effective in controlling varicella aggregation outbreaks. A gradual implementation of a 2-dose Var Vimmunization strategy in children is recommended for effective prevention of varicella.