Each year, around 1,000 Americans are hospitalized due to the severe form of West Nile virus, transmitted through mosquito bites. On average, another 1,500 people are diagnosed after developing symptoms, though experts believe that up to 80% of infections in the U.S. go undetected.

There is no vaccine for West Nile virus. Most cases are mild, presenting flu-like symptoms and a rash. However, in about 1 in 150 cases, the virus can affect the brain and nervous system, leading to complications such as brain swelling, brain damage, or death. Approximately 100 people die from West Nile virus infections in the U.S. annually.