A newly identified strain of influenza, referred to as the K subclade of H3N2, is sweeping across the United States, leading to a concerning surge in flu cases and symptoms that can last up to seven days. According to the Centers for Disease Control and Prevention (CDC), illness levels are categorized as “very high” in 32 states, and at least nine children have died from the flu this season.
Health experts emphasize that this variant is highly contagious and brings harsher symptoms, particularly severe fevers. Dr. Mark Loafman, chair of Family and Community Medicine at Cook County Health, noted that patients are experiencing prolonged fevers, stating, “You feel ill, you feel sick and you worry that you’re not getting better.” The current CDC data reveals that one in three flu tests is returning positive, marking a significant increase of 21 percent from the previous week and a staggering 76 percent rise compared to last year.
Rising Cases and Severe Symptoms
Since September, influenza A has dominated flu samples in the U.S., with a remarkable 97 percent attributed to this category. Notably, 86 percent of these samples are H3N2, and 91 percent of H3N2 samples belong to the newly emerging subclade K. Dr. Loafman expressed concerns about the potential for further spread, especially as holiday gatherings and indoor activities increase during winter months.
Dr. Santina Wheat, a family physician with Northwestern Medicine, highlighted that flu cases might further escalate as students return to school following winter breaks. Symptoms of this flu strain differ from typical patterns, with some patients experiencing fevers that do not respond to common treatments like Tylenol or Motrin. Dr. Juanita Mora, national spokesperson for the American Lung Association, warned, “It is one of those high fevers that won’t break.”
Patients are also facing an array of symptoms, including a persistent cough, vomiting, diarrhea, and severe joint and muscle aches. Dr. Loafman noted an increase in gastrointestinal issues among adults with the flu, which is more commonly seen in children.
Public Health Response and Recommendations
In response to the rising number of flu cases, public health officials are urging vaccinations as the most effective means to prevent severe illness from flu, COVID-19, and RSV. Although the current flu vaccine was not specifically designed for the new variant, Dr. Loafman emphasized its importance, stating, “The vaccine isn’t perfect…but it certainly mitigates the severity of illness.”
He explained that those who receive the flu shot tend to have milder symptoms, are less likely to be hospitalized, and experience quicker recoveries. The Illinois Department of Public Health has reported a significant number of hospital admissions related to respiratory illnesses caused by this flu strain, particularly affecting children aged 5 to 17.
Recent data from New York indicates over 72,000 flu cases reported in the week of December 20, representing a historic high for the state. The implications are serious, with health officials warning that dehydration poses a significant risk to those infected, particularly among children and older adults. Dr. Mora advised that individuals exhibiting signs of dehydration should seek immediate medical attention.
Looking at trends from earlier flu seasons, experts noted that the dominant strain in the United States appears to have originated from Australia, where it prompted a severe flu season. Research indicates that the K subclade was first sequenced in New York in June 2025 before spreading to other regions.
As the flu season continues, health authorities remain vigilant, urging the public to stay informed and take preventive measures to protect themselves and their families. With the potential for further spread, health experts are emphasizing the importance of vaccination and early intervention for those showing symptoms of severe illness.
