Epidemiological characteristics of varicella and vaccination status in the cases in Jing’an District， Shanghai from 2017 to 2019

Objective To 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.

Methods Descriptive 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.

Results A 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）.

Conclusion We 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.