In an article published in NEJM in May 2023 experts from the Division of Vector-Borne Diseases presented a call to “revisit the need for human West Nile virus (WNV) vaccines”. WHO suggests that, although 80% of infected patients do not show symptoms, the virus can cause a fatal neurological disease in humans. Usually transmitted through bites from mosquitoes, the virus finds its natural hosts in birds.
The burden of disease
From a US perspective, the authors comment that since initial detection of WNV in the country in 1999, it has become the “leading cause of domestic arthropod-borne viral (arboviral) disease”. According to CDC data it has caused more than 55,000 cases of human disease and 2,600 deaths between 1999 and 2021.
“In addition to morbidity and mortality, WNV disease results in substantial costs to patients and society.”
The estimated hospital costs per year reach an average of $59.9 million for the 3109 California residents hospitalised between 2004 and 2017. However, the threat is not limited to the US; it is an “ongoing public health threat” across the world.
Containment and prevention efforts
The authors recognise the “development and expansion” of WNV-specific surveillance and control programmes. Despite these, a “consistently high burden of disease” continues throughout the US each year. Unfortunately, the occurrence at a subnational level is “both geographically focal and sporadic”, which makes it difficult to anticipate outbreaks.
Current preventative efforts include “personal protective measures to reduce vector exposure” and “community-based mosquito control programmes”. However, these approaches are limited according to the authors, who suggest that adherence is “often low”. Reactive programmes are effective but are “costly” and “typically initiated only after many cases”. Additionally, proactive strategies are hard to implement.
Vaccines for horses not humans
Several veterinary vaccines for WNV have been licensed. However, no human vaccines have progressed past Phase I or II clinical trials. The authors identify “several factors” as hindrances to progression. These include “challenges with designing and implementing efficacy studies”, safety concerns, and anticipated costs. Thevchallenges are “not unique” and can be overcome with solutions used for other vaccines, such as “alternative licensing pathways”.
The paper concludes that the past two decades have “demonstrated that current prevention strategies are not enough”.
“WNV vaccination would be more effective in preventing WNV disease and related deaths. Lessons from the development of other vaccines can be applied to move WNV vaccine candidates further through development to ensure the availability of safe and effective vaccines.”