Prospects for development of a vaccine against the West Nile virus

Vaccination provides the ultimate measure for personal protection against West Nile disease. The development of a West Nile vaccine for humans is justified by the uncertainty surrounding the size and frequency of future epidemics. At least two companies (Acambis Inc. and Baxter/immuno) have initiated research and development on human vaccines. West Nile encephalitis has also emerged as a significant problem for the equine industry. One major veterinary vaccine manufacturer (Ft. Dodge) is developing formalin-inactivated and naked DNA vaccines. The advantages and disadvantages of formalin-inactivated whole virion vaccines, Japanese encephalitis vaccine for cross-protection, naked DNA, and live attenuated vaccines are described. A novel technology platform for live, attenuated recombinant vaccines (ChimeriVax) represents a promising approach for rapid development of a West Nile vaccine. This technology uses yellow fever 17D as a live vector for envelope genes of the West Nile virus. Infectious clone technology is used to replace the genes encoding the prM and E structural proteins of yellow fever 17D vaccine virus with the corresponding genes of West Nile virus. The resulting virion has the protein coat of West Nile, containing all antigenic determinants for neutralization and one or more epitopes for cytotoxic T lymphocytes. The genes encoding the nucleocapsid protein, nonstructural proteins, and untranslated terminal regions responsible for replication remain those of the original yellow fever 17D virus. The chimeric virus replicates in the host like yellow fever 17D but immunizes specifically against West Nile virus.