To analyze the incidence rate of varicella outbreak in a kindergarten in Nanjing city, to find out the risk factors of varicella outbreak and to evaluate the protection effect of varicella vaccine.

A retrospective case analysis was conducted on 54 patients with varicella who appeared in a kindergarten in Nanjing between March 19, 2018 and June 27, 2018. Among them, there were 33 boys and 21 girls, aged from 3 to 25 years, with infants aged from 3 to 6 years, and the average age of infants was (5.30±0.88) years. The incidence and vaccination of varicella among the kindergarten students and teachers were collected through active search and questionnaire survey. Descriptive study and cohort study were used for analysis.

A total of 54 cases were reported, with an incidence rate of 7.74%. The outbreak involved 10 classes and 2 teachers, with the highest incidence rate of 34.3%. The first case occurred on March 26, 2018, and the epidemic lasted for 68 days. In this outbreak, the protection rate of varicella vaccine was 58% (RR=0.42, 95CI% : 0.22~0.80).

The incidence of varicella outbreaks is relatively high in kindergartens and other collective units. Relevant institutions should strengthen the monitoring and management of infectious diseases in schools, kindergartens and other collective units, and strengthen the training of knowledge related to infectious diseases.