To investigate the event of varicella outbreak and the protective effect of varicella vaccine to provide scientific basis for formulating prevention and control strategies.

Searches were conducted between 1 September 2018 and 23 January 2019 for typical varicella-like rashes(papules or herpes or crusts) among children and faculty members in a kindergarten; pharyngeal swab specimens from 8 cases were collected for etiological detection; using the platform of "Questionnaire Star" and "Jiangsu Provincial Comprehensive Service Management Information System for Vaccination" , information about varicella vaccination of all children in six classes were collected, and a retrospective cohort study was conducted to investigate the effect of vaccine protection.

A total of 106 cases of varicella were found, with a prevalence of 14.5% (104/717) in children and 2.8% (2/72) in faculty members; the first case was a child in Class 6, Grade 1; the case was onset on September 6, 2018, and the epidemic lasted for 4 months. The epidemic curve showed a proliferation pattern, and the cases could be divided into eight generations. The outbreak spread to 8 classes, and the incidence of the outbreak ranged from 17.5% to 58.5%; the incidence of varicella was 12.9% (8/62) in those vaccinated with varicella vaccine, 54.4% (81/149) in those not vaccinated with varicella vaccine. The vaccine protective rate was 76% (95%CI=54% to 88%). Of 37.5% (3/8) of throat swab specimens were positive for varicella-zoster virus nucleic acid.

It is difficult to prevent and control varicella outbreaks in a low immunization population. The protective effect of varicella vaccine is of significance. It is suggested to further strengthen the publicity of varicella vaccination and incorporate the vaccination of children with varicella into the expanded immunization program.