Jan. 8, 2026 – Flu season is here – and it's shaping up to be a bad one.
So far in 2025-26, the flu has caused 11 million illnesses, 120,000 hospitalizations, and 5,000 deaths – more than twice as many cases and nearly twice as many hospitalizations and deaths as the CDC reported at this time last year. Older adults (ages 65 and up) and children under 4 are hardest hit, but even healthy young adults can fall severely ill.
With schools and workplaces reopening this week, the situation could get worse soon.
"It's still early days, and unfortunately, this could be a particularly bad season," said Frederick G. Hayden, MD, a professor emeritus of infectious diseases at the University of Virginia School of Medicine.
An uptick in flu cases is typical this time of year, but "what's surprising is how quickly those cases are rising," said Andrew Pekosz, PhD, a professor of molecular microbiology and immunology at Johns Hopkins Bloomberg School of Public Health. Cases usually take four to six weeks to spike. Right now, "many places are going from virtually no significant influenza cases to being above epidemic levels within two weeks."
Pekosz is closely following data from the CDC and from health departments in states including Maryland, California, and New York.
"In New York, the flu season started a little earlier," Pekosz said. "We're sort of seeing it unfold there." On Jan. 2, New York reported the highest number of flu hospitalizations ever recorded in a single week. That could be a sign of what's to come.
Behind the vast majority of cases (91%) is a new flu virus variant called influenza A (H3N2) subclade K, which has genetic mutations that help it evade the immune system.
Why This Flu Variant Spreads So Fast
All flu viruses evolve to be more infectious, but H3N2 does so especially fast. Flu seasons dominated by H3N2 variants tend to have higher infection rates than those dominated by other strains.
Subclade K has mutated to sneak past your body's natural defenses: antibodies.
Anytime you get a flu shot or infection, your body creates antibodies to help you fight back the next time you encounter the virus. The most effective antibodies bind to proteins on the virus's surface to block it from attaching to and entering cells in your respiratory tract, Pekosz said.
Subclade K has mutations at two "hot spots" where antibodies would normally bind to protect you from disease, said Pekosz. This may reduce antibody binding, allowing the virus to attach to cells, replicate, and cause infection.
How Bad Can the Flu Get?
"Influenza itself is a pretty strong disease," said Pekosz. "Most people who have it will tell you they're out for a couple of days, and it really does take a lot out of you."
One common complication is a secondary infection, such as bronchitis or pneumonia.
"You get this one-two punch," said Pekosz. "A bacterial infection comes in to take advantage of that damaged environment, and you get that double whammy of respiratory problems."
Other times, the immune system overreacts. "You respond too well to the infection," Pekosz said, and your immune response ends up damaging respiratory tract cells.
In severe cases, these complications can be fatal.
They're most common in people who have certain health conditions – such as heart disease, asthma, and liver disorders. But sometimes, even seemingly healthy people can fall severely ill and die. Research shows that certain genetic factors may influence a person's immune response to the flu.
Your First Line of Defense: a Flu Shot
If you haven't had a flu shot yet this season, it's not too late – and it's still one of the best defenses against the flu, Pekosz said. This year's flu shot doesn't include subclade K, but it does cover a different H3N2 subtype along with strains of H1N1 and influenza B.
When the vaccine isn't a perfect match for the flu variant in circulation – as is the case this season – more people get sick, Pekosz said. But "even in these mismatched vaccine years, the vaccine does provide protection against severe disease."
"There are more than just these two antibody binding sites that protect you from flu," he said. "There are other antibody binding sites that are helpful; there are other parts of your immune response that are helping fight off the virus. And in many ways, the vaccine does prime you to respond even to these mismatched virus strains."
Early data from the U.K.'s 2025-26 flu season – which has also been dominated by subclade K – suggest that the intranasal flu vaccine (available for ages 2-49) is 72% to 75% effective in protecting children from severe flu.
"If we could get greater use of that vaccine in school-aged children, that would have a protective effect – not only for them, but also for their contacts," Hayden said.
Vaccination is especially critical for people at higher risk of severe disease: young children, adults over 65, and those with medical conditions that make it harder to fend off infection. "Those are the people that really benefit the most from vaccination, even in a mismatched vaccine year," said Pekosz. (This week, the CDC revised its childhood vaccination schedule, changing the flu vaccine recommendation from universal to "shared clinical decision making," a change that medical organizations, including the American Academy of Pediatrics, say could confuse the public about the importance of vaccination. The AAP and the American Academy of Family Physicians continue to recommend the flu shot.)
Plus, the shot may protect you from H1N1 and flu B strains, which could emerge later in the season, Pekosz said.
Here's What Else Experts Recommend You Do
Adults 65 and older, and people with health conditions
Why they're at risk: "As you get older, your immune system is just a little bit slower to respond to infections," said Pekosz. "Individuals over the age of 65 have not just age, but a lot of other secondary medical conditions that predispose them to developing more severe influenza."
What to do:
- Break out the mask. The flu spreads mainly through droplets released into the air when people cough, sneeze, or talk. A mask can block some of those droplets. Be especially careful in grocery stores, airports, and other crowded places. "Anything you can do in terms of masking, keeping some social distancing, particularly over the next couple of weeks, would be smart," said Pekosz. (Both Pekosz and Hayden are masking in public right now.)
- Ask your pharmacy about antivirals. Antiviral medications such as Tamiflu (oseltamivir phosphate) can help make the flu less severe when taken within 48 hours of your first symptoms. Before you get sick, ask your pharmacy whether they have these medications in stock and how to get a prescription.
"Some pharmacies will give you a prescription of Tamiflu or one of the other antiviral drugs simply if you have a positive over-the-counter at-home test. Others require a prescription," said Pekosz. "Know what it takes to get these antivirals and figure out what your plan will be while you're healthy, because if you start to feel sick, the faster you can get them, the better."
Children
Why they're at risk: "Children appear to be targeted by this strain of flu," Pekosz said. Kids have a shorter history of flu exposure – especially H3N2 – potentially leaving their immune systems unprepared to fight back, he said. Plus, day cares and schools can easily spread the flu.
What to do:
- Keep your kids away from sick people. Obvious, but essential.
- If symptoms develop, watch for red flags. The good news: "Most kids will respond to the infection, be sick for a few days, and then recover," Pekosz said. But some kids may become severely ill and require medical care. Warning signs include extreme lethargy and trouble breathing that doesn't get better after suctioning their nose. "We do see pediatric deaths from influenza every year," Pekosz said. "Paying attention to those signs that the illness is getting worse is really, really critical." If you have any concerns at all, go to the emergency room or call 911.
The whole family
- Order food instead of dining out. Germs spread easily when people are talking and eating in close quarters. Check your state public health department website, and if flu levels are rising in your area, consider avoiding crowded places, gatherings, and events for now, Pekosz said.
- Test early if someone in your home gets sick. A flu test from a health care provider or an at-home test from the drugstore can help confirm an infection. If the test is positive, consider antivirals for the infected person and everyone else in the household – these medications can reduce the risk of spread, Hayden said.
- For higher-risk people, don't wait. If a person with significant health challenges develops symptoms rapidly, ask a health care provider whether antivirals should be started right away, even before testing.
"If a higher-risk person can't get rapid access to health care or testing done, it's really important, if they become ill, to get on treatment as rapidly as possible," Hayden said. "Treatment for influenza, with the antivirals that we have, is time dependent."
