Objective: To understand the vaccination of varicella attenuated live vaccine (VarV) among students in collective institutions, to provide a basis for analying the protective effect of vaccination. Methods: All collective institutions with chickenpox epidemic and post exposure vaccination in Jing an District from 2017 to 2019 were investigated. All students( n =6 473) in the affected class were included. Vaccination status and the incidence information of disease were collected to analyze vaccine effectiveness (VE). Results: The proportion of study subjects without an immunization history decreased year by year, and 7.5% in 2017, 7.2 % in 2018, and 4.9% in 2019. The proportion with a history of one dose prior to exposure in cases was 90.0%, it was lower than 93.5% in the non cases ( χ 2=6.53, P <0.05). The proportion with one dose as post exposure prophylaxis in cases was 8.3%, it was much lower than 44.1% in the non cases ( χ 2=179.06, P <0.01). The proportion with one dose as post exposure prophylaxis in secondary cases was 28.6%, much lower than 44.1% in the non cases ( χ 2=9.44, P <0.01).Unvaccinated ones and the second dose as post exposure prophylaxis ones in cases had the highest rate of varicella development (11.0%), a history of one dose prior to exposure and one dose as post exposure prophylaxis in cases had the lowest varicella rate (1.0%).There was a clear protective effect within two years after one dose of VarV inoculation, VE was 63.1%(95% CI =11.0%-84.7%). Conclusion The vaccine effectiveness of one dose VarV was limited. Post exposure prophylaxis as early as possible was highly effective in decreasing secondary attack rate.

ObjectiveTo analyze the epidemiological characteristics and the vaccination status of the cases in Jing’an District from 2017 to 2019， so as to provide reference basis for the strategy of prevention and control of varicella epidemic. MethodsDescriptive epidemiological methods were used to analyze the epidemiological characteristics of varicella in Jing’an District. The differences between the vaccinated group and the unvaccinated group were compared by statistical methods. ResultsA total of 2 508 cases of varicella were reported with an average annual incidence of 78.7/10⁵ from 2017 to 2019. There was no significant difference in the incidence among the three years（χ²=5.535，P=0.063）. There were 1 308 males and 1 200 females， and sex ratio was 1.1∶1. The highest incidence occurred in the age group from 5 to 9 years old （562 cases， 479.3/10⁵）. Two annual peaks occured in May and November. The incidence in the aged 18 and below decreased year by year. There was significant difference in the proportion among the three years（χ²=78.129， P<0.001）. The median interval from vaccination to onset was 5 years among the vaccinated cases. There was significant difference in the cases who received two doses of vaccine in three years（χ²=90.902， P<0.001）. ConclusionWe should strengthen the monitoring system and pay more attention to the epidemiological characteristics of varicella. The protective efficacy of two-doses vaccine needs to be systematically evaluated.