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

Abstract

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.

Keywords: Central India; Hospitalization rates; Impact assessment; Incidence estimates; Infectious encephalitis; Japanese encephalitis.

Fig. 1

Incidence rate estimates of acute encephalitis syndrome (AES) and Japanese encephalitis (JE) cases per 100,000 population before and after implementation of two doses of JE vaccine in routine immunization schedule in Maharashtra based on public health reported cases. a Incidence estimates at the state level. b Incidence estimates in vaccinated and nonvaccinated study districts. Error bars (whiskers) indicate 95% confidence levels for estimates

Fig. 2

Incidence rate estimates per 100,000 children per year in study districts in Maharashtra and Telangana as per the JE vaccination status during 2018–2020. a Acute Encephalitis Syndrome (AES). b Japanese Encephalitis (JE)

Fig. 3

Incidence rate estimates of acute encephalitis syndrome (AES) and Japanese encephalitis (JE) cases per 100,000 population among children and adults during 2015–2016 and 2018–2020 after the implementation of routine immunization of infants with two doses of the live-attenuated SA 14-14-2 JE vaccine. a Study districts in Maharashtra and Telangana. b Vaccinated and nonvaccinated study districts in Maharashtra

Fig. 4

Incidence rate estimates of acute encephalitis syndrome (AES) and Japanese encephalitis (JE) cases per 100,000 population among both children and adults after the implementation of routine immunization with two doses of the live-attenuated SA 14-14-2 JE vaccine among infants during 2018–2020. a Incidence estimates for the study districts in Maharashtra and Telangana. b Incidence estimates for the JE-vaccinated and nonvaccinated study districts in Maharashtra