Impact of the expanded program on immunization on the incidence of Japanese encephalitis in different regions of Mainland China: An interrupt time series analysis

Abstract

In 2008, Mainland China included the Japanese encephalitis (JE) vaccine in the Expanded Program on Immunization (EPI) to control the JE epidemic. However, Northwest China experienced the largest JE outbreak since 1994 in 2018, and the effects of the EPI in different regions are unclear. Therefore, we used an interrupted time series design to evaluate the effects of the EPI in different regions. In this study, β₁ and β₁+β₃ represented the slope or trend of the JE incidence before and after the EPI, respectively; β₂ was the level change of the JE incidence immediately after the EPI; β₃ represented the slope change of the JE incidence before and after the EPI. We found that the JE incidence in all regions showed a decreasing trend before the EPI (β₁<0.000, P<0.05). The JE incidence in Mainland China (β₂=-7.669, P<0.05), East China (β₂=-9.791, P<0.05), Central China (β₂=-10.695, P<0.05), South China (β₂=-6.551, P<0.05) and Southwest China (β₂=-2.216, P<0.05) decreased by 7.669/100,000, 9.791/100,000, 10.695/100,000, 6.551/100,000 and 2.216/100,000 immediately after the EPI, and the EPI had short-term effects on the JE incidence in these regions. The slope of the JE incidence in Mainland China (β₃=0.272, P<0.05), East China (β₃=0.337, P<0.05), Central China (β₃=0.381, P<0.05), South China (β₃=0.254, P<0.05) and Southwest China (β₃=0.081, P<0.05) increased by 0.272, 0.337, 0.381, 0.254 and 0.081 after the EPI, and the EPI had long-term effects on the JE incidence in these regions. The JE incidence in many regions (excluding North China) showed a decreasing trend after the EPI (β₁+β₃ <0.000). Northwest China (GDP from 2008 to 2020 ranked last in Mainland China) and Southwest China (GDP from 2008 to 2020 ranked fifth in Mainland China), with underdeveloped economy, used to be low-epidemic regions of JE, but they have become high-epidemic regions in recent years. Economic development may contribute to the geographic variations in the effects of the EPI. Therefore, it is significant for JE control in Mainland China to increase support for underdeveloped regions and adjust the vaccine strategy according to the new epidemic situation of JE.

Keywords: Expanded program on immunization; Incidence; Interrupted time series analysis; Japanese encephalitis; Mainland China; Vaccine.