Impact of Japanese encephalitis vaccination in Shijiazhuang on the incidence of Japanese encephalitis: an interrupted time series analysis

Abstract

Objective To analyze the impact of Japanese encephalitis(JE) vaccine administration on the trend of JE incidence. Methods Interrupted time series analysis (ITSA) and segmented regression analysis (SRA) using JE incidence data in Shi Jiazhuang from 1949 to 2019 were conducted to quantitatively assess short-term and long-term effect of JE vaccination. Results There was a statistical significant increasing trend of JE incidence from 1949 to 1968 (β1=0.19, t =-2.01, P =0.048). With the introduction of vaccine from 1969 to 2019, JE incidence decreased immediately (β2=-7.83, t =-2.97, P =0.004) in 1969; And the average decreasing slope of JE incidence (β1+β3) was -0.04/lakh with the significant difference (β3=-0.23, t =-3.24, P =0.002). However, JE incidence increased due to the outbreak in 1969-2019 (β4=3.87, t =2.36, P =0.007). Further analysis using data on the period of pre-immunization program(1969-2007) showed that the JE incidence decreased (β2=-7.22, t =-2.98, P =0.01) in 1969 and the continuous decreasing slope was 0.29 (β3=-0.29, t =-2.73, P =0.008); And JE incidence did not increase due to the outbreak (β4=4.65, t =0.72, P =0.476) in this period. However, compared with the period of pre-immunization program, in the period of immunization program, no statistically significant decreasing of JE incidence was found in 2008 (β2=-2.89, t=-1.56, P=0.169) and in this period (β3=-0.03, t=-1.16, P=0.252); Meanwhile, JE incidence still increased due to the outbreak in this period (β4=3.62, t=4.21, P=0.001). Conclusions The implementation of vaccine administration in Shi Jiazhuang has made remarkable effectiveness in the JE control. However, the immunization strategies need to be adjusted according to the change of the vulnerable population of cases moving from younger children to the older adult.