At least 15 million Americans have come down with the flu — and 7,400, including 17 children, have died from the illness — during the 2025-26 flu season so far, making it one of the most brutal in recent memory.
“Last year [2024-25] was our worst flu season in almost two decades, and I was hoping we might have a mild flu season this year,” says Thomas Russo, MD, State University of New York distinguished professor and chief of infectious diseases at the Jacobs School of Medicine and Biomedical Sciences at the University of Buffalo. “That does not appear to be the case. Flu season started two weeks early, cases are rising very rapidly across almost the entire country, and we’re still not close to peak.”
Hospitalizations due to flu are also on the rise — 180,000 people have already been admitted, though the worst of the season is yet to come. (There were between 610,000 and 1.3 million flu-related hospitalizations during the 2024-25 flu season.)
“At our hospital right now, we have 10 times the number of people admitted for flu as for COVID and RSV [respiratory syncytial virus],” says Scott Roberts, MD, assistant professor of infectious diseases at Yale School of Medicine and associate medical director of infection prevention at Yale New Haven Health.
And academic experts anticipate even more illness by mid-January, as people return from holiday gatherings, where close contact facilitates the spread of viruses.
Here, infectious disease doctors answer 10 common questions about the spread of flu and how to shore up your defenses.
1. What’s behind the ferocity of the flu season this year?
The culprit is a strain of influenza A(H3N2) virus called subclade K, Roberts says. This strain is responsible for 90% of the season’s flu cases.
Despite some media reports, this year’s flu is not a super flu.
“There’s no evidence yet that this particular strain is more severe than other strains, but it is more mutated,” Roberts says. “There are seven mutations that are different from what was expected and put in the vaccine. It’s different enough that it’s bypassing some of our baseline immunity and therefore leading to more infections.”
Subclade K emerged during the summer and was first detected in Europe after the strains of flu used to formulate this year’s flu shot were already chosen.
2. How effective is this year’s flu vaccine?
Since subclade K mutations allow the flu to evade some of the flu vaccine’s protection, its effectiveness is muted.
“Some people define effectiveness as ‘You got the shot, did you get the flu?’” says Michelle Barron, MD, professor at the University of Colorado School of Medicine and senior medical director of infection prevention and control for UCHealth. “And that’s how we typically define vaccine effectiveness. But in a really good year, the flu vaccine is at best 60% to 65% effective at preventing you from getting sick. From some of the early reports, it’s somewhere between 30% to 40% this season.”
Although the flu shot may not keep you from succumbing to the illness, Barron says, it lessens your odds of having a severe case, keeps you out of the hospital, and shortens the duration of illness, even in flu seasons like this one, when the vaccine is less than a perfect match for the virus.
“Any protection you get from the vaccine is better than zero protection you get without it,” says Robert H. Hopkins Jr., MD, professor of internal medicine and pediatrics at the University of Arkansas for Medical Sciences and medical director of the National Foundation for Infectious Diseases.
3. How robust has uptake of the flu vaccine been so far for the current flu season?
The childhood vaccination rate in 2025 was similar to that of 2024 — almost 43%. “But if you look back over the last several years, we’ve seen a decline in childhood flu vaccination rates, going back to the 2019, 2020, and 2021 seasons,” Hopkins says. Rates were higher among younger children (51.7% of children ages 6 months to 4 years) than for older children (45% of those who were ages 5 to 11) and adolescents (34% of children ages 12 to 17).
Among adults, rates of influenza vaccination increased slightly in 2025, Hopkins says, but “statistically, it’s about the same” — about 43%. As one might expect, “the rates of flu vaccination are higher as you get into older adult age groups, as opposed to younger groups,” he adds.
There were significant differences in uptake by state and by region. The Northeast had more states falling within the higher 47.2% to 57.6% vaccination range than any other region. Virginia, Iowa, the District of Columbia, Colorado, Georgia, and Hawaii were the only locations outside the Northeast with this level of coverage. Southeastern states (including Florida, Alabama, Mississippi, and Louisiana) and Western states (including Arizona, Nevada, and Idaho) had the lowest vaccination coverage, ranging from 16.2% to 37.3%, says Hopkins.
4. Is it too late to get a flu shot?
There’s still plenty of flu season ahead, so experts recommend that people get the vaccine if they haven’t already.
“We think that the vaccine is still going to afford a reasonable degree of protection from severe disease, hospitalizations, and bad outcomes,” Russo says. “Getting the flu vaccine is still critical as part of our prevention plan.”
It’s particularly important for people with compromised immune systems and chronic diseases. Because it takes 10 days to two weeks for the body to mount an immune response to fight the flu virus, the sooner you get the jab, the better.
Although preventing the flu is reason enough to get a flu shot, Barron says, there are other benefits. Vaccination is linked to a lower risk of having a heart attack, 2022 research shows. People who received the flu shot had a 34% lower risk of experiencing a major cardiovascular event in the 12 months following vaccination. Other data show a lower risk for Alzheimer’s in the four years following vaccination.
5. What do we know about symptoms of this year’s flu?
Importantly, this year’s flu virus doesn’t seem to cause more severe illness than in previous years — it just makes more people sick. Regardless of the season, the flu produces fever, chills, body aches, and a “run-over-by-a-truck” degree of fatigue. Cough, sore throat, and runny nose may start initially or develop later, Barron says. Children often experience gastrointestinal symptoms such as nausea and diarrhea. In general, flu illness is more severe among people with compromised immunity, underlying cardiac, pulmonary, or renal diseases, or cancer, and the very young and old.
“A common question we get is, ‘How do I know it’s flu versus anything else?’” says Roberts. “With flu, people will describe a sudden-onset fever — so sudden that some people can pinpoint exactly what they were doing the moment the fever arrived. With COVID or RSV there’s usually a more gradual buildup of symptoms.”
If complications develop, there can be new signs.
“When people do die from the flu, it’s often from things like bacterial pneumonia,” Barron says. “The way you recognize that is your fever has gone away and then two days later you suddenly start getting fevers again or you have trouble breathing.” People with such symptoms should see a doctor immediately.
6. How important is it to get tested when flu-like symptoms strike?
Testing is a wise move, because, depending on what’s causing the illness, there may be beneficial treatments, including antiviral medications such as Tamiflu (oseltamivir) for flu and Paxlovid (nirmatrelvir or ritonavir) for COVID.
“Think about having a few over-the-counter flu and COVID test kits sitting around the house, so you can know what you have and can provide that information to your health care professional to help them make the best recommendations to get you through this,” Hopkins advises. There are combination tests that identify both COVID and flu, and others that cover the three top seasonal respiratory viruses — flu, COVID, and RSV.
7. How do antiviral flu medications work?
Tamiflu and other antivirals work by shortening the duration of illness by a day or two. They may also reduce viral shedding, so patients are less likely to pass the flu to others.
“They limit progression,” says Barron. “They help decrease the viral load over time causing less of the inflammatory process in your body. Ultimately our goal is to keep patients from developing pneumonia.”
Antivirals work best if treatment starts within 48 hours of the onset of symptoms, so it’s important to get tested sooner rather than later.
Unfortunately, Roberts says, “one thing I see a lot with physicians in the community is somebody comes in with flu and the doctor says, ‘You're okay. Let’s see how you do, and we’ll start the treatment if you get worse.’ But by then you’re out of the treatment window.”
Even if they are past the 48-hour window, high-risk patients will get some benefit by taking a prescribed treatment, Barron says. They can also be used to prevent infection when someone has been exposed to flu. For instance, if an individual gets sick with flu, others in the same household can take an antiviral drug to prevent transmission.
8. What are the alternatives to Tamiflu, and the pros and cons of each?
In addition to Tamiflu, there are newer antiviral medications for flu, including Xofluza (baloxavir). With Tamiflu, patients take a pill (or liquid dose) twice a day for five days. It’s approved for individuals two weeks of age and older and is the preferred treatment for women who are pregnant or postpartum. Xofluza is a single-dose tablet, approved for people age five and older.
Xofluza has several key advantages. “There are some flu strains out there that are Tamiflu-resistant because it’s been around for a long time,” Roberts says. “Xofluza overcomes that.”
The new drug also appears to produce fewer side effects. With Tamiflu, “people can have stomach upset, nausea, vomiting,” Roberts says. “Kids can experience neuropsychiatric effects.”
However, Xofluza can be more expensive than Tamiflu — as much as $200 for the pill, without insurance — which puts it out of reach for many patients.
There are two other newer antivirals: Rapivab (peramivir), an intravenous infusion that’s used in the hospital, and Relenza (zanamivir), which is administered through an inhaler twice a day for five days and costs around $90. Both have mostly mild side effects.
9. How long does the vaccine’s protection last? What if you got the shot at the end of the summer?
Experts agree that the vaccine should be effective throughout the flu season, which typically ends in April or May, even if people received a flu shot in the early fall.
“It’s individualized,” says Barron. “But if you got it in September or even August, you should be well protected through the spring.”
10. How can you prevent the spread of flu and other viral illnesses that are circulating?
“First and foremost, if you’re sick, stay away from others,” Hopkins says. “You don’t want to spread what you have.”
Frequent handwashing is crucial, he says, adding, “If you cough or sneeze, I encourage people to cover their mouths with a tissue or with their sleeve, rather than with their hands, because that helps to avoid the spread of those respiratory droplets.”
If someone in the household is sick, disinfecting surfaces can help prevent others from coming down with the flu, Roberts says.
Also, now is a good time to consider wearing a mask, “particularly if you’re high risk and are going to be in crowds or in situations where people are likely to be sick,” Hopkins says.
“We’re looking at a potentially severe flu season,” says Hopkins. “That doesn’t mean panic, but let’s take care of each other. Let’s think about our neighbors, friends, and family members, and get vaccinated. And let’s try to stay active and eat well so we’re best able to get through this illness if we get it.”
