Flu activity is surging across the United States this winter, reaching levels not seen in decades, according to the latest data from the Centers for Disease Control and Prevention (CDC). The agency reports that the ongoing flu and cold season is proving especially severe, with the number of medical visits, hospitalizations, and deaths climbing sharply as 2025 draws to a close.
In the week ending December 27, the CDC recorded that 8% of all doctor visits were related to flu or flu-like symptoms the highest percentage since nationwide tracking began in 1997. Hospitalizations spiked by 48% from the previous week, bringing total flu-related hospital admissions to roughly 120,000 and deaths to around 5,000 so far this season.
Health experts are pointing to a newly identified mutation, known as subclade K, as a potential factor behind the rapid escalation. The variant appears to be fueling widespread transmission, leading to warnings that this flu season could become one of the most intense in recent years.
CDC data indicates that flu activity is now considered “high” nationwide. Nearly one-third (33%) of the 70,757 flu tests conducted during the final week of December tested positive, a steep jump from just 9% at the beginning of the month. The highest positivity rates—exceeding 45%—were seen in several Mountain West states, including Colorado, Montana, North Dakota, South Dakota, Utah, and Wyoming.
The Northeast is also facing significant strain, with states such as New York, Massachusetts, and North Carolina experiencing “very high” levels of flu activity. Wastewater data compiled by WasteWaterSCAN, a Stanford University-led surveillance initiative, supports these findings. It recorded a 146% increase in viral concentration nationwide throughout December, suggesting the flu virus is spreading rapidly through more communities.
As of December 30, the CDC’s modeling projected rising infection rates in 17 states, steady levels in seven, and declines or expected declines in 24 others. While the overall national trend remains upward, experts emphasize that regional differences may affect how long the surge continues into January.
Public health officials continue urging vaccination, emphasizing that flu shots remain the most effective defense against severe illness and hospitalization. With cases still climbing, the next few weeks will be critical in determining how severe this flu season ultimately becomes.
