The present invention relates to novel vaccines containing (whole-inactivated) West Nile Viruses and/or West Nile viral proteins derived therefrom, produced on human cells, wherein the human cells comprise a sequence encoding at least one early region-1 (E1) gene product of an adenovirus. The cells are preferably cultured in suspension to very high densities and under serum-free conditions. Herein, it is disclosed that use of such cells results in high titers of West Nile Virus produced.