Potential use of attenuated langat E5 virus as a live vaccine -- long term protection against Russian spring-summer encephalitis virus in mice

A single inoculation of Langat E5 virus provides 90-100% protection in mice against 3200-16000 lethal doses of Russian Spring-Summer Encephalitis (RSSE) virus when challenged 18 or 24 months later. The observed protection is found in the absence of neutralizing antibody (NA) against RSSE virus at the time of challenge but is associated with anamnestic NA response. Immunized mice have low titer short duration viremia. Immunized mice have late first detection and much lower multiplication in the brains, even though traces of virus could be detected in the brain up to 3 weeks following challenge. The observed protection results from sensitization due to immunization and quick host response following RSSE challenge resulting in significantly altered viral pathogenesis. Long term cross protection studies reported in this study and before coupled with the experience of the use of attenuated Langat E5 virus in humans volunteers suggests to its further testing as a live vaccine for prophylaxis against various members of Russian Spring-Summer virus complex throughout the world.