West Nile virus season in the United States has officially entered its most dangerous window — the weeks of August and September when transmission peaks nationally — and the 2026 season is already the worst early start in more than two decades.
The CDC confirmed 48 West Nile virus cases across 23 states as of June 30, 2026, nearly five times the historical average of approximately 10 cases at that point in the season. Of those 48 cases, 38 were classified as neuroinvasive disease — the severe form in which the virus reaches the brain or spinal cord.
