Japanese encephalitis vaccine: need of the hour in endemic states of India

Abstract

Japanese encephalitis (JE), a mosquito-borne arboviral infection, is the leading cause of viral encephalitis in Asia. Most worldwide cases of JE are reported annually from the People's Republic of China (PRC), Korea, Japan, Southeast Asia, the Indian subcontinent, and parts of Oceania. JE virus is transmitted by Culex mosquitoes particularly of the Culex vishnui group (C. tritaeniorhynchus). Humans get infected following a bite by an infected mosquito. However, since humans cannot transmit infection, further spread does not take place between humans. Most human cases of JE are asymptomatic. Infection leads to overt encephalitis in only 1 of 20-1,000 cases. Encephalitis usually is severe, resulting in a fatal outcome in 25% of cases and residual neuropsychiatric sequelae in 30% of cases. The World Health Organization (WHO) estimates that there are at least 50,000 serious cases of the disease in Asia each year. Approximately 10,000 of those subjects die, mostly children. JE Outbreaks have been reported from most states and union territories in India through the years. In India, the risk is highest in the monsoon and post-monsoon period. The proposed immunization strategy for India is based on the regional experience and builds off of the three pillars of JE control, i.e., Surveillance for cases of encephalitis, Vector control and Vaccination. The Cell Culture Derived Live SA-14-14-2 Vaccine is based on a stable neuro-attenuated strain of JE virus (SA-14-14-2). It was first licensed for use in 1988 in People's Republic of China, and current usage is over 60 million doses per year. It is also licensed in India, South Korea and Nepal. JE vaccines are available in 5-dose vials as a lyophilized powder that looks like a milky-white crisp cake; this is rehydrated with 2.5 mL diluent. The dose is 0.5 mL administered subcutaneously for all ages and containing not less than 5.4 log PFU of live JE virus (JEV).