Japanese Encephalitis: Evaluation of Vaccine Impact in Uttar Pradesh, India

Abstract

Japanese encephalitis (JE) virus is the leading cause of vaccine-preventable encephalitis and a significant cause of disability in Asia and the western Pacific. JE is endemic in many parts of India and the state of Uttar Pradesh (UP) contributed approximately 75% of the cases in India over the last three decades. Since 2006, UP has used the live attenuated SA-14-14-2 vaccine (CD-JEV, Chengdu Institute of Biological Products) to prevent JE. To measure the impact of vaccine introduction in UP, the number of confirmed JE cases in 1- to 15-year-old children and vaccination coverage were analyzed by year for 40 districts in UP. Vaccine-induced protection against JE seems to have come primarily from campaign coverage, with the only distinct downward trend in disease occurring in the initial 7 high-risk districts where a second high-coverage catch-up campaign targeting children aged 1- 15 years occurred 4 years after the first campaign in 2006 (p-value <0.005). There was 25% reduction in JE cases for every 10% increase in vaccine coverage in these districts. However, there was no statistically significant impact of vaccine on the number of JE cases in a combined analysis for all districts over the study time period. Limited routine immunization coverage, especially in areas where the susceptible populations were large, was one potential reason behind inefficient vaccine impact. There is a need for catch-up campaigns in districts with poor routine immunization coverage as well as for robust routine immunization programs to sustain protection in each year’s new birth cohort.