WESTERN EQUINE ENCEPHALITIS AND EASTERN EQUINE ENCEPHALITIS BIVALENT VACCINE EFFICACY STUDY

Kenneth Plante¹, E. Wang, Ph.D. ¹, I. Frolov, Ph.D. ², S. Weaver, Ph.D. ¹

¹Department of Pathology, UTMB; ²Department of Microbiology, University of Alabama

Introduction: Chimeric viruses allow for safe and immunogenic live-attenuated vaccine candidates. Chimeras containing Sindbis nonstructural genes and either WEE or EEE structural genes are shown to ellicit an immune response while remaining non-pathogenic to the infected animal. Objective: WEE and EEE share some topographical range, and animals and humans may become exposed to both. We wanted to determine if separate WEE and EEE vaccines, givien in conjunction, remain safe and offer protection against both viruses. We also wanted to determine which ratio of the separate vaccine candidates provide the best all around protection against both viruses while maintaining the total vaccine dose of 10⁶ pfu. Methods: The study used NIH Swiss and Swiss Webster mice infected SC at six weeks of age. Groups consisted of 5 mice and were monitored and weighed weekly. Four weeks post vaccination blood is drawn retro-orbitally and PRNT-80 titers are completed with the sera collected. The mice were then given a lethal challenge and monitored for illness. Results: All mice sero-converted and had high PRNT 80 titers. Mice that received different ratios of the combined vaccines showed a positive PRNT-80 titer against both WEE and EEE. Mice also survived a lethal challenge with a virulent strain of each virus. Conclusion: This study shows that these vaccine candidates are not only safe to be given in tandem, but also offer protection against both viruses. Supported by NIAD through the Western Regional Center Excellence for Biodefense and Emerging Infectious Disease NIH Grant Number - U54 AI057156.