Japanese encephalitis and vaccines: past and future prospects.

The Japanese encephalitis virus is the main cause of encephalitis in Asia. The vectors are mosquitoes. Every year 30,000 to 50,000 cases and 10,000 deaths from Japanese encephalitis are reported, and estimates go up to 100,000 cases. No effective antiviral therapy exists to treat this flavivirus infection. For prophylaxis vaccines are available. In Asia numerous vaccines are used regionally. The production of the only vaccine that was internationally licensed, JE-VAX, was ceased in 2005. Therefore a shortage of Japanese encephalitis vaccines might occur before new generation vaccines based on cell cultures will be available. An inactivated Vero cell-derived vaccine based on the Beijing-1 strain is developed in Japan by Biken and Kaketsuken. Another promising vaccine candidate is the inactivated whole-virus vaccine IC-51 (Strain SA14-14-2) by the Austrian company Intercell. The third interesting vaccine candidate being in the late stages of clinical trials is the genetically engineered, chimeric and live-attenuated vaccine ChimeriVaxtrade mark-JE by the UK/USA-based company Acambis. The new vaccines in the pipeline show promising results and market licensures are expected in the near future. Showing excellent tolerability, these vaccines will not only be used in the population living in endemic areas where the risk of infection is extremely high, but also for travellers and military personnel.