Japanese Encephalitis outbreak in Assam, Northeastern India, January to August 2022

Abstract

An outbreak of Japanese encephalitis (JEV) was detected in Assam, Northeast India, on July 1st, 2022. The source of human infection is known to be zoonotic transmission from culicine mosquitoes through bites. A total of 434 cases of JEV were recorded between July 1 and September 23, 2022, in 17 separate districts within Assam, India. The precise demographics of these JEV cases remain unknown. The case fatality rate in Assam during this outbreak was 21.43% (93); however, underreporting may occur. JEV is vaccine-preventable, and a vaccine was introduced under the Universal Immunization Programme (UIP) in endemic states to cover children at risk, but not adults. Such serious outbreaks have occurred in the past, with an outbreak in 2006 causing 6061 cases and 1500 deaths. Reports from the current outbreak suggest the cause of the outbreak may be due to prolonged floods resulting in water stagnation in Assam. An unusual feature of the current outbreak is the relatively high CFR and significant neurological involvement. Some key questions include: what is the demographic distribution of JEV cases in Assam? What is the vaccine coverage in Assam? How protective is the JEV vaccine?