Varicella outbreaks in schools and kindergartens in Shanghai, China from 2011 to 2020

BACKGROUND: Varicella is a contagious disease caused by varicella-zoster virus and varicella vaccine (VarV) is the most effective way to prevent and control varicella. Despite high VarV coverage there were still varicella outbreaks in schools and kindergartens. We aim to analyze the epidemiological characteristics of varicella outbreaks in Huangpu District, Shanghai, China from 2011 to 2020. METHODS: For varicella outbreaks, case information and vaccination history were collected. Mann–Kendall test and descriptive methods were used to analyzed the trend and epidemiological catachrestic of varicella outbreaks. RESULTS: A total of 57 varicella outbreaks were reported from 2011 to 2020, including 30 outbreaks (52.6%) in primary schools. The results of the Mann–Kendall trend test (z = 1.97, p = 0.049) showed an upward trend in the number of cases during the study period, but the trend change was not statistically significant. Emergency vaccination was carried out in 42 (73.7%) outbreaks which influenced the duration of the epidemic (F = 4.53, p = 0.0379). A total of 573 varicella cases were reported, including 357 cases (62.3%) who had received at least one dose of varicella vaccine. CONCLUSIONS: The number of varicella outbreaks has not changed significantly in the decade from 2011 to 2020. The strategy of varicella vaccination, the development and application of varicella vaccine, and the control measures after the occurrence of varicella outbreaks need to be optimized. In addition to vaccination, as a disease transmitted by contact, quarantine measures, good personal hygiene, environmental disinfection, and ventilation are also important.