West Nile Virus Vaccines

West Nile Virus Vaccine Candidates May 2025

The U.S. Food and Drug Administration (FDA) has not approved West Nile virus (WNV) vaccines for people as of May 2025. However, active human clinical studies include vaccine candidates: two live attenuated chimeric, one DNA, one recombinant subunit, and two inactivated whole-virus vaccines.

In phase 2 trials, the live attenuated recombinant yellow fever vaccine strain expressing the premembrane and envelope (prM–E) genes of WNV (ChimeriVax-WN02, Sanofi Pasteur) was found to have a good safety profile and immunogenicity even in older age groups after a single dose.

The HydroVax-001 vaccine candidate consists of a hydrogen peroxide inactivated whole virion (WNV-Kunjin strain) adjuvanted with aluminum hydroxide.

"Our experience over the past two decades has demonstrated that current prevention strategies are insufficient to reduce the ongoing WNV disease burden. WNV vaccination would be more effective in preventing WNV disease and related deaths," wrote a Perspective published by the NEJM on May 4, 2023. "The benefits of live vaccines, including durability of immunity and the need for only one dose, will need to be weighed against potential safety concerns."

West Nile Virus Outbreaks

Since 1999, West Nile Virus (WNV) has become the leading cause of arthropod-borne viral (arboviral) disease in the United States, says the U.S. Centers for Disease Control and Prevention (CDC). West Nile is a nationally notifiable condition in the U.S. As of January 2025, the CDC reported 1,466 WNV cases in 49 states in 2024.

In Europe, the European Centre for Disease Prevention and Control (ECDC) shows that there have been 715 locally acquired cases of WNV across 15 countries in Europe in 2024, surpassing the number reported in the same period in 2023 and Europe's 10-year average. As of September 2024, 51 people had died as a result of the infection. A study published in the Journal of Experimental Medicine on June 22, 2023, found that about 35% of patients hospitalized for WNV also carried autoantibodies that neutralize type 1 interferons, the signaling proteins deployed by various cells in the fight against viruses.

In May 2025, a research program by the  UK Health Security Agency and the Animal and Plant Health Agency identified fragments of West Nile Virus genetic material in mosquitoes collected in Britain for the first time.