The relatively low number of West Nile cases has been a roadblock for development of a vaccine. In Phase III clinical trials, a significant number of individuals has to be infected and enrolled in order for a vaccine or treatment to demonstrate efficacy. Only a proven effective vaccine will be approved for use in humans, explained Deepta Bhattacharya, PhD, a professor of immunobiology at the College of Medicine – Phoenix. “That was one of the reasons why the SARS-CoV-2 vaccines were able to be deployed so quickly: at the time Pfizer and Moderna were testing the vaccine, there was a ton of community spread,” Dr. Bhattacharya said.