Efficacy, duration, and onset of immunogenicity of a West Nile virus vaccine, live Flavivirus chimera, in horses with a clinical disease challenge model

Summary Reasons for performing study: West Nile virus (WNF) is a Flavivirus responsible for a life‐threatening neurological disease in man and horses. Development of improved vaccines against Flavivirus infections is therefore important. Objectives: To establish that a single immunogenicity dose of live Flavivirus chimera (WN‐FV) vaccine protects horses from the disease and it induces a protective immune response, and to determine the duration of the protective immunity. Methods: Clinical signs were compared between vaccinated (VACC) and control (CTRL) horses after an intrathecal WNV challenge given at 10 or 28 days, or 12 months post vaccination. Results: Challenge of horses in the immunogenicity study at Day 28 post vaccination resulted in severe clinical signs of WNV infection in 10/10 control (CTRL) compared to 1/20 vaccinated (VACC) horses (P