The present invention relates to compositions comprising humanized antibodies or fragments thereof that immunospecifically bind to one or more antigens of a flavivirus, particularly of West Nile Virus (WNV) and methods for preventing, treating or ameliorating symptoms associated with a flavivirus, particularly of West Nile Virus (WNV) infection utilizing said compositions. In particular, the present invention relates to methods for preventing, treating or ameliorating symptoms associated with WNV infection, said methods comprising administering to a human subject an effective amount of one or more humanized antibodies or fragments thereof that immunospecifically bind to a WNV antigen. The present invention also relates to detectable or diagnostic compositions comprising humanized antibodies or fragments thereof that immunospecifically bind to a WNV antigen and methods for detecting or diagnosing WNV infection utilizing said compositions.