Abstract:

Objective To explore the changes in epidemiological characteristics of varicella in Jinnan District after the inclusion of varicella vaccine，live（VarV） in local immunization programs in Tianjin，provide a reference for further optimizing varicella vaccination strategies and prevention and control measures. Methods Using the data from the 2023-2024 period to represent the management phase of the Expanded Programme on Immunization（EPI），and the data from the 2015-2016 period to represent the non-EPI management phase，the descriptive statistics was used to analyze the epidemic characteristics of varicella and the correlation between VarV vaccination rate and incidence rate during the two periods. Results From 2015 to 2024，a total of 5 933 cases of varicella were cumulatively reported in Jinnan District，the ratio of male to female reported cases was 1.27∶1. The average annual reported incidence rate was 69.98/100 000，with an increasing and then decreasing trend. The difference was statistically significant（χ²=649.444，P<0.01），with the lowest at 30.49/100 000 in 2022 and the highest at 109.49/100 000 in 2019. The average annual reported incidence rate in EPI period（63.05/100 000） was lower than that in non-EPI period（70.59/100 000），the difference was statistically significant（χ²=6.817，P<0.01）. The disease incidence in both periods followed a seasonal pattern with two distinct peaks，mainly in winter（November to January of the following year） and Spring（April to May）. Compared to the non-EPI management period，the highest reported incidence rate shifted from 9~<10 years to 15~<20 years in EPI management period. The incidence rates declined across all age groups under 10 years old，with statistically significant differences between two periods observed in all groups except for 8-<9 years. The primary settings for varicella outbreaks transitioned from kindergartens and primary schools to predominantly middle schools and higher educational institutions. For the birth cohorts of 2007-2015，the coverage rate of the first dose of VarV ranged from 76.41% to 90.58%，while the second dose coverage rate ranged from 9.64% to 50.11%. For the birth cohorts of 2016-2023，the coverage rate of the first dose of VarV ranged from 95.27% to 99.46%，and the second dose coverage rate ranged from 85.41% to 98.89%. The 377（born after 2005） cases could be found immunization history accurately in 2024， 55.43% had received one dose of VarV，with an average interval of （12.90±3.38）years from vaccination to disease onset，and 11.41% had received two doses of VarV，with an average interval of （7.67±2.30）years from vaccination to disease onset. Conclusions After the implementation of the two-dose VarV vaccination strategy in the immunization program in Jinnan District of Tianjin，the incidence of varicella among children under 10 years old significantly decreases，with a shift in the age of onset toward older groups. The varicella outbreaks gradually occur more frequently among senior-grade students. The vaccination coverage of the two-dose VarV in the 2016-2023 birth cohort remains at a high level，while the second-dose VarV coverage in the 2007-2015 birth cohort is relatively low.

Key words: Varicella, Immunization program, Varicella attenuated live vaccine, Epidemiological characteristic, Coverage rate, Incidence rate