A critical appraisal of Ixiaro^® – a cell-derived inactivated vaccine for Japanese encephalitis

Abstract

Japanese encephalitis is a disease prevalent across a huge swathe of southeast Asia. The number of reported cases of the disease is increasing in countries that do not have a vaccination program, but in contrast, is decreasing in countries that have implemented mass vaccination programs. Clearly vaccination is having some impact, and although visitors to the area are generally thought to be at low risk, vaccination is recommended for those staying 1 month or longer. Until recently, the only licensed vaccine available to them, JE-VAX ® , was made from virus propagated in mouse brain, and among Western Hemisphere recipients of this vaccine, many side effects and adverse events were reported, and production of the vaccine was discontinued in 2007. A new vaccine, Ixiaro ® , has recently been licensed. The vaccine comprises inactivated virus, previously propagated in Vero cells, adsorbed onto an alum adjuvant. In extensive clinical trials in both adult and pediatric populations, Ixiaro ® has proven non-inferior to JE-VAX ® in terms of immunogenicity and seroconversion, but with an improved safety and tolerability profile compared with JE-VAX ® .