Research Highlight

Co-circulating JEV strains question vaccine efficacy

doi:10.1038/nindia.2012.166 Published online 20 November 2012

Researchers have reported the first case of co-circulation of two genotypes — GI and GIII — of Japanese encephalitis virus (JEV) in the West Bengal state of India. The finding emphasises the need to review the efficacy of earlier vaccines that protect only against the GIII strain. The researchers suggest that an outbreak is quite likely in the state if this vaccine fails to protect sufficiently against GI of JEV.

JEV, a mosquito-borne pathogen, is the causative agent of Japanese Encephalitis (JE), a neurotropic killer disease and a major cause of viral encephalitis worldwide. JE was first reported in West Bengal in 1973. Since then it is being reported every year from different districts of the state despite available vaccines. The researchers say this indicates either partial coverage of the vaccine or emergence of mutated/new strain of JEV.

To understand the JEV genotype distribution, they conducted a molecular epidemiological study on 135 serum/cerebrospinal fluid (CSF) samples from clinically suspected patients with Acute encephalitis syndrome (AES), admitted to different district hospitals of West Bengal in 2010.

Phylogenetic analysis based on complete envelope gene sequences of 13 isolates showed the emergence of JEV genotype I (GI) co-circulating with genotype III (GIII).

The researchers say the efficacy of the vaccine (derived from JEV GIII strain SA-14-14-2) to protect against emerging JEV GI needs careful evaluation in view of the report of co-circulation of more than one strains.


  1. Sarkar, A. et al. Molecular evidence for the occurrence of Japanese encephalitis virus genotype I and III infection associated with acute Encephalitis in Patients of West Bengal, India, 2010. Virol. J. doi: 10.1186/1743-422X-9-271(2012)