An aggressive and unusually early wave of influenza is sweeping across parts of the United States, propelled by a mutated virus that surfaced months ahead of the normal winter peak, CNN reported.
While seasonal flu activity typically begins in the South before traveling northward, this season’s outbreak took hold along the West Coast first. Dr. Alex Greninger, who leads the Division of Infectious Disease Diagnostics at the University of Washington, told CNN that the season kicked off roughly two and a half months earlier than what is standard. In Washington state, about one in 10 people tested for the virus was positive last week, creating illness volumes typically seen in midwinter.
Spreading across the country
The early uptick is not confined to the Pacific Northwest. In a region covering California, Nevada, Arizona and Hawaii, testing positivity reached at least 10 percent last week, according to CNN. Dr. Caitlin Rivers, an epidemiologist at the Johns Hopkins Bloomberg School of Public Health, told the network that the virus is actively expanding eastward, with southern states rapidly catching up.
Walgreens reported the season is running approximately four weeks ahead of recent years, with pharmacy counters dispensing more antiviral medications and cold remedies than during the same period in 2025, CNN reported. Nationally, about 2.1 percent of outpatient medical visits were linked to influenza-like symptoms last week, according to the U.S. Centers for Disease Control and Prevention. While that figure remains below the national baseline, CDC figures showed a five percent jump in infections during the opening week of October compared to the prior year, WMUR reported.
Mutated H1N1 strain evades immunity
Laboratory testing indicates the early wave is dominated by the H1N1 subtype, which previously sparked a global pandemic in 2009. Greninger told CNN the current virus traces back to Asia and represents around 98 percent of the patient samples tested in his laboratory.
The strain developed a genetic change labeled G155E, which enables the virus to better slip past human immune defenses, CNN reported. The variant previously triggered heavy disruption in Japan, shuttering schools and child care facilities as cases mounted among young children.
Because the mutation surfaced after public health panels selected the viral strains for this year’s immunizations, the available shots do not provide a seamless match, Greninger explained. Most U.S. flu vaccines are cultivated in chicken eggs, an economical process that requires months of preparation. While a newly approved messenger RNA flu vaccine could enable faster manufacturing in the future, production costs remain a hurdle, he said.
Urgent call for vaccinations
Health specialists stressed that annual immunization remains crucial despite the genetic variation. Dr. Sharon Vuppula, an infectious disease physician with Southern New Hampshire Medical Center, told WMUR that anyone six months of age and older should receive a flu shot promptly. She said the vaccine is generally 40 to 60 percent effective at preventing illness and critically limits the severity of infections, curbing hospitalizations for high-risk populations.
Common symptoms include sudden fever, muscle fatigue, body aches and coughing. Because the body takes roughly two weeks to construct protective antibodies after inoculation, medical professionals advise against delaying vaccination.
How the rest of the season will unfold remains uncertain. Greninger told CNN that following an autumn crest in H1N1 infections, the U.S. could face a secondary surge during the traditional peak months of January, February or March.
