Incidence of Japanese Encephalitis and Acute Encephalitis Syndrome Hospitalizations in the Medium-Endemic Region in Central India.

BACKGROUND: We estimated the incidence of Japanese encephalitis (JE) and acute encephalitis syndrome (AES) following routine immunization with the live-attenuated SA 14-14-2 JE vaccine. METHODS: We implemented enhanced surveillance of AES and JE hospitalizations in endemic districts in Maharashtra and Telangana States during 2015-2016 and 2018-2020. We estimated incidence and compared differences in the incidence of JE and AES between two states, and vaccinated and unvaccinated districts during two study periods. We also considered secondary data from public health services to understand long-term trends from 2007 to 2020. RESULTS: The annual AES incidence rate of 2.25 cases per 100,000 children in Maharashtra during 2018-2020 was significantly lower than 3.36 cases per 100,000 children during 2015-2016. The six JE-vaccinated districts in Maharashtra had significantly lower incidence rates during 2018-2020 (2.03, 95% CI 1.73-2.37) than in 2015-16 (3.26, 2.86-3.70). In addition, the incidence of both JE and AES in two unvaccinated districts was higher than in the vaccinated districts in Maharashtra. Telangana had a lower incidence of both JE and AES than Maharashtra. The AES incidence rate of 0.95 (0.77-1.17) during 2018-2020 in Telangana was significantly lower than 1.67 (1.41-1.97) during 2015-2016. CONCLUSIONS: The annual incidence rate of Japanese encephalitis was < 1 case per 100,000 children. It indicated accelerated control of Japanese encephalitis after routine immunization. However, the annual incidence of acute encephalitis syndrome was still > 1 case per 100,000 children. It highlights the need for improving surveillance and evaluating the impacts of vaccination.

Effectiveness of Japanese encephalitis vaccination among children in central India.

Japanese encephalitis (JE) disease among children continues in central India despite vaccination implemented in the routine immunization program. Therefore, we planned to estimate the JE vaccination effectiveness among children by undertaking a 1:2 individually-matched population-based case-control study from August 2018 to October 2020. The laboratory-confirmed JE cases aged 1-15 years were enrolled along with neighborhood controls without fever and encephalitis matched on the residence area, age and sex. The JE vaccination history was enquired from parents and verified independently from the vaccination cards available at home and records at health facilities. We enrolled 35 JE cases and 70 matched controls. The vaccination effectiveness of 86.7% (95% confidence interval [CI]: 30.8-94.7) was estimated on the per-protocol analysis of 31 case-control sets. The screening method provided an effectiveness of 89.5% (CI: 78.9-94.7) on using the population vaccination coverage of 90% reported earlier in the same area. In conclusion, JE vaccination offered a moderate level of protection among children in JE medium-endemic central India, similar to reports from high-endemic areas in India. The operational aspects of vaccination program implementation need to be evaluated to assess the impact of vaccination on the disease burden of JE in medium-endemic regions of India.