Influenza arrived early this year, popping up on the west coast “about two and a half months earlier than normal”, says Dr Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota – a timeline not seen since the 2010 season.
And while the Centers for Disease Control (CDC) still considers flu activity overall to be low, with 16,000 recorded flu-related hospitalizations so far, it expects infections to keep rising in the coming weeks as the virus spreads through the midwest and east coast.
While factors like travel patterns may have contributed to this early season, “there’s not a completely ironclad explanation for why this has occurred,” notes Dr Amesh Adalja, an infectious disease specialist at Johns Hopkins Center for Health Security.
Timing isn’t the only unusual thing about this year’s flu – here’s what you need to know.
What’s different about this year’s flu: a mutated H1N1 virus
This year’s dominant flu strain is an H1N1 virus carrying a mutation known as G155E. According to Adalja, there’s no evidence that the mutation makes the virus more likely to cause severe illness, though it resembles features of H1N1 strains that circulated before 2009.
Early research suggests that teens and young adults under 25 “have less immunity” to this strain, Adalja says – the virus may be “more able to get around some of the immunity that people have from prior infections and prior vaccinations”, he says.
So far, there has been one reported US pediatric influenza-associated death this season, of an elementary-aged child from outside the Denver metro area. An estimated 24,000 people, 198 of them children, died of flu-related illness in the 2025-26 season.
According to Dr Alex L Greninger, head of the division of infectious disease diagnostics at the University of Washington, differences in how people respond to the flu have more to do with the individual infected – people with diminished cardio respiratory capacity, for example – than with the virus itself. “If you’ve recently had heart disease, when the flu comes it can push you over the edge in terms of heart and lung function,” he says.
The vaccine was developed before this mutation – but is still worth it
Every February, the World Health Organization (WHO) brings together experts who review global flu data and create an informed, but not completely certain, forecast as to which three flu variants they expect to see dominate the northern hemisphere in the coming winter.
“We make vaccines for flu the same way we made them in the 1940s; we use very old technologies that require a long lead time,” says Adalja.
This year, their forecast was off. “This particular variant really emerged after we already had chosen what was in the vaccine,” notes Osterholm, meaning that this year’s vaccine is a weaker match against infection.
But, Osterholm says, the question is not about whether the vaccine works or doesn’t work, but about it being less protective. Being vaccinated is like “having your seatbelt attached against the flu. It protects you against severe disease, hospitalization, and death.”
This year’s weak vaccine-flu match is not related to the US leaving the WHO. “Even though the US left the WHO, which is the wrong decision for a number of reasons, the CDC did participate in the WHO strain selection process,” says Adalja. “So it wasn’t as if they were not part of that decision-making … The strains that are used in the northern hemisphere that are being administered in the United States are identical to the ones being administered in Canada and Mexico, for example.”
This is the first year that an mRNA-based flu vaccine, developed by Moderna, is also available to the public. Called mFlusiva, the vaccine is recommended for adults 50 and older, a group that faces the highest risk from flu, and has been shown to produce milder reactions than mRNA Covid vaccines, Osterholm says.
While mFlusiva was also developed prior to the flu’s mutation, Adalja hopes that mRNA technology will help future vaccine strain selections occur closer to the start of flu season, improving the quality of the match.
When should people get vaccinated this year?
Because it takes about two weeks after a vaccine for your body to create enough antibodies to protect you, the time is near to guard yourself before the holiday season.
“Now is the time to get your vaccine,” says Osterholm. “Especially those under 25 should be encouraged to get vaccinated earlier than usual, meaning now.”
Osterholm encourages everyone to get both a Covid booster and their flu shot, saying he got his on the same day. It’s “not unexpected” to feel unwell for a day or two after your shots, he says. “Just know it’s a lot better to have a reaction, than to get the flu.”
If you get sick, at-home antigen tests for influenza, flu A, flu B and respiratory syncytial virus are all available. Experts agree that testing is worthwhile because knowing what strain you have can help your doctor prescribe useful antivirals like Tamiflu or Xofluza, which can reduce serious illness, hospitalizations and recovery time.
When ill, it’s important to stay at home to mitigate flu spread and to protect vulnerable people; if you must leave your home, Osterholm recommends wearing an N95 mask.
Where can people find trustworthy guidance on the flu?
While once people could reliably find information about the flu vaccine on the CDC’s website, this year, it’s a bit more complicated. In 2025, health secretary Robert F Kennedy Jr fired every member of the CDC’s vaccine advisory committee and appointed his own picks. A federal court has since halted the new panel’s votes. As a result, the systems that normally advise Americans have stalled, with the CDC relying on last year’s flu recommendations.
“There is no [Advisory Committee on Immunization Practices]. It doesn’t exist in a sense,” says Osterholm.
Other major medical groups have stepped in to provide reliable information to the public. In September, the American Academy of Pediatrics, the American Academy of Family Physicians, the American College of Obstetricians and Gynecologists and the Infectious Diseases Society of America issued coordinated recommendations. They drew on an evidence review by the Vaccine Integrity Project, an initiative at Osterholm’s research center. All four groups advise a flu shot for everyone six months and older, including pregnant people in any trimester.
Adalja advises people to start with those groups rather than the CDC. “Some of the data from the CDC is valid and can be trusted, but some of it can’t,” he says. For a layperson, “it’s hard to know whether this is something that’s been tainted by RFK Jr.”
And while this year, America’s exit from the WHO didn’t make a difference in the flu vaccine’s makeup, Adalja worries the break “will likely pose a problem when novel strains of flu arise outside the United States” in the future, he says.
It’s impossible to predict the trajectory of any flu season, though holiday travel is often linked with a boost in flu infections. Still, experts aren’t ruling out “a normal season in January and February”, Greninger conjectures. What’s clear is that precautions against the flu, from vaccination to hand-washing, masking, and staying home when sick, are as critical as ever.
