Single-dose, fast-acting vaccine candidate against western equine encephalitis virus completely protects mice from intranasal challenge with different strains of the virus.

Western equine encephalitis virus (WEEV) causes a fatal infection of the central nervous system in humans and horses. However, neither human vaccine nor antiviral drug is available. We found previously that immunization of mice with two doses of an adenovirus-vectored WEEV vaccine, Ad5-WEEV, confers complete protection against homologous WEEV challenge. In this paper, we report that a single-dose injection of Ad5-WEEV completely protected mice against both homologous and heterologous strains of WEEV at 1 week after immunization. In addition, mice immunized with Ad5-WEEV were protected when challenged at 13 weeks after a single-dose immunization. Therefore, the protection conferred by Ad5-WEEV is rapid, cross-protective, and long-lasting. These results warrant further development of Ad5-WEEV into an emergency vaccine that can be used during a natural outbreak or a bioterrorism attack.