Impact of inclusion of varicella vaccine into the immunization program on the incidence of varicella

ObjectiveTo analyze the epidemiological characteristics of varicella in Minhang District， Shanghai from 2013 to 2022， and to evaluate the impact of adjusting the varicella vaccination program to a two-dose regimen and its inclusion in the Shanghai immunization program on the incidence of varicella.MethodsData on reported varicella cases from 2013 to 2022 in Minhang District were collected. Interrupted time series analysis and segmented regression models were used to analyze the changes in varicella incidence before and after the adjustment of varicella immunization strategies.ResultsFrom 2013 to 2022， the average annual incidence of varicella was 76.58/100 000， with the highest incidence in 2017 （119.21/100 000） and the lowest in 2022 （27.02/100 000）. The varicella incidence exhibited seasonal patterns with peaks occurring from March to June and October to January of the following year. Prior to the adjustment of varicella immunization strategies （2013‒2017）， the varicella incidence showed an upward trend （z=2.20， P=0.03）， while after the adjustment （2018‒2022）， a adownward trend was observed （2018‒2022） （z=-2.25， P=0.02）. Interrupted time series analysis showed that following the adjustment of varicella immunization strategies， an immediate change of -33.91/100 000 （t=-4.35， P