In India, the main cause of encephalitis is the Japanese encephalitis virus. From 2006 to 2011, the SA 14-14-2 vaccination was administered in 104 endemic regions in a gradual way to reduce the rising prevalence and deadly outbreaks. Because there is no data available prior to 2008 on the number of Japanese encephalitis (JE) cases excluding Acute Encephalitis Syndrome (AES), a four-year average of JE vs. AES cases reported between 2008 and 2011 were calculated, and the value was used to calculate the percentage of JE cases out of AES cases from 1994 to 2007. Data study from 1994 to 2017 revealed a significant rise in JE cases following the implementation of immunisation in 2006. Because the JE immunisation was only administered in a few areas, comparing the vaccinated district to the non-vaccinated district would be a better way to assess the impact of vaccination. However, the data on JE is only available at the state level. As a result, Tamil Nadu, where district-level JE data is available beginning in 1993, was utilised as a model state to assess the impact of immunisation.

Despite the fact that statistics for the whole state of Tamil Nadu indicated a rising trend, an examination of data for vaccinated areas indicates that the rise was attributable to an increase in JE cases in non-vaccinated regions. It demonstrates that there was a decrease in JE case occurrences in vaccinated regions of Tamil Nadu in particular, and India as a whole, following the introduction of the SA 14-14-2 vaccine.

Reference:https://www.tandfonline.com/doi/full/10.1080/21645515.2018.1564435