This flu season seems to be going from bad to worse.
CDC data from the week ending December 27 estimated that 8.2 percent of outpatient visits nationwide were for flu-like illness. Previous highs approached the 8 percent mark last year and during the 2009 swine flu pandemic.
The percentage of flu tests coming back positive jumped by 33 percent over the previous week, and about 11 million cases total have already been recorded this flu season.
At least 45 states and the District of Columbia are now experiencing flu at levels that are high to very high, with only Montana, South Dakota, Vermont, and West Virginia experiencing low to moderate rates of flu transmission. (The status of Nevada is uncertain due to insufficient data.)
“It looks like we are in for a rough flu season,” says Mark Rupp, MD, an infectious disease specialist and the interim chair of the department of internal medicine at the University of Nebraska Medical Center in Omaha. “Influenza-like illness trends are sharply up and we probably have a few weeks before flu peaks.”
Flu Has Already Killed 5,000 People in the U.S.
While most people get through the flu with about a week of rest, fluids, and care, many have much more severe illness. Already this season, flu has led to 120,000 hospitalizations and 5,000 deaths.
“Flu usually involves the upper airways, but when it gets into the lungs, it can turn deadly,” says Dr. Rupp. “This is particularly true for those who have certain risk factors, such as old age [those over 65], underlying cardiorespiratory disease, or immunosuppression.”
While the rate of severe influenza is lower in children than in the elderly, every year children and young adults also die from influenza. So far nine children have died from flu this season. Pediatric deaths for 2024–25 totaled 289, which was higher than any season since the CDC started this tracking in 2004, according to the American Academy of Pediatrics.
Sojib Zaman, PhD, an assistant professor of health sciences at James Madison University in Harrisonburg, Virginia, warns that in some instances, even seemingly healthy people can become seriously ill or die from flu.
“Sometimes the virus causes severe lung injury very quickly, or a secondary bacterial infection [usually pneumonia] strikes,” he says. “Also, ‘healthy’ people may have risk factors that they do not realize they have, and delays in seeking care or antivirals can matter.”
A New Flu Mutation Is Driving the Surge
A rise in flu activity can be expected this time of year due to holiday travel and children going back to school, spreading respiratory viruses to classmates and taking the infection home to others.
A major factor adding fuel to the fire this season, however, is an unexpected mutation in the flu virus that allows it to better evade any immune defenses. A new version of influenza A (H3N2) called subclade K is highly contagious and accounts for the vast majority of influenza cases in all parts of the United States and across the Northern Hemisphere, according to Andrew Pekosz, PhD, a virologist with the division of infectious diseases at Johns Hopkins Bloomberg School of Public Health in Baltimore.
Although some have called this strain a “super flu,” Dr. Pekosz considers the label misleading as there is no evidence at this time indicating that subclade K causes more severe illness.
“The rate of hospitalization appears quite consistent with that of other influenza seasons; it’s just that this virus is causing a lot more infections, and we are seeing a proportional rise in severe cases,” he says.
Vaccine Is Not a Perfect Match but Provides Significant Protection
Many months ago, when manufacturers decided on the formula for this season’s vaccine, subclade K was not yet on the radar, so this year’s shot is considered somewhat of a mismatch.
“The K subclade has ‘genetically drifted’ from the H3N2 strain that is in the flu vaccine, so this could be contributing to the number of cases,” says Rupp.
Still, because the vaccine contains components that protect against the H3N2 strain in general, the shot is expected to provide significant protection against serious illness.
“Most of the deaths and hospitalizations for influenza are in unvaccinated people,” says Pekosz. “If you aren’t vaccinated you will be more likely to get infected and sick.”
The CDC reports that overall, only about 43 percent of children and adults have received this year’s flu shot.
Samantha Picking, PharmD, the senior director of immunizations for the pharmacy chain Walgreens, views low vaccination rates as contributing to higher than usual flu cases.
“Vaccination rates continue to lag in comparison to pre-pandemic years,” she says. “When fewer individuals are vaccinated, we lose the benefits of herd immunity, which helps protect vulnerable groups and limit the overall spread of the virus.”
Is It Too Late to Get a Flu Shot?
Dr. Picking adds that it’s not too late to get vaccinated as flu season typically lasts into the spring. But getting the shot sooner than later is recommended as it takes about two weeks for it to become fully effective.
Along with vaccination, the following measures can also help reduce flu transmission:
- Wash hands frequently.
- Avoid touching your face.
- Stay home if you’re sick and stay away from those who are sick.
- Wear a well-fitted N95 mask (especially if you are in a high-risk group) when in enclosed spaces with other people, such as on airplanes or mass transit.
- If you get sick, check with your pharmacy or doctor about getting influenza antiviral drugs, as they can help you feel better and reduce your risk of severe disease if taken within 48 hours of symptom onset.
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