US sees early flu activity, peaking Covid-19 and West Nile trends

Early Flu Metrics and Global Comparisons

National flu metrics are ticking up, including emergency department visits, with increases appearing particularly early in the West, according to data from the Centers for Disease Control and Prevention. Typically, flu metrics do not start increasing until October or November, and activity usually begins in the Southeast before spreading nationally. The U.S. is not alone in this trend, as the U.K., Japan, and other Northern Hemisphere countries are also observing early increases. Epidemiologists look to the Southern Hemisphere’s winter season for clues, but the recent southern winter produced a mixed bag of results. Argentina recorded its highest number of flu-like illness cases in a decade with an early start, while Australia, New Zealand, and Fiji experienced an unusually quiet window before an unexpected surge in August and September. Australia’s late-surging 2025 season caused waning immunity to stretch later into the year, creating a delayed pattern.

Covid-19 Wastewater Levels and Declining Mortality

Wastewater data tracked by the Centers for Disease Control and Prevention indicates that Covid-19 levels have clearly peaked at the national level, though a few Midwestern states are still seeing rising numbers before anticipated declines. The summer peak reached a level comparable to winter numbers but remained below last summer’s peak. With reduced spread and increased population immunity, deaths continue to fall by about 54% each year. Current projections indicate that Covid-19 will contribute to approximately 9,100 deaths this year, which is less than half of the annual mortality caused by the flu. Public health guidance emphasizes that while population-level impacts are declining, the vaccine remains important for high-risk populations as doses become widely available.

West Nile Virus Trends in the Southwest

Mosquito-borne disease activity nationwide has been quieter this year compared to last year, despite the West Nile season starting earlier than any year since 2004. The major exception is the Southwest, where Phoenix and California report numbers well above last year, according to the California Department of Public Health. Mosquito activity typically peaks in August and trends downward into autumn, driven by local factors including heat, standing water, and animal host immunity. Public health authorities advise residents in active regions to use insect repellent at dusk and eliminate standing water weekly until the first sustained cold snap causes mosquitoes to go dormant or die off.