By Jessica Nix, Bloomberg
An influenza outbreak swamped the US as the year came to an end, reaching the highest levels since the Covid-19 pandemic and hitting children and teenagers especially hard.
At least 11 million people have contracted the flu so far this season and 5,000 people have died, according to data released Monday by the US Centers for Disease Control and Prevention. Doctor and emergency department visits for flu-like illness are at the highest levels since before the pandemic hit in 2020, and the agency classified the current outbreak as “moderately severe” for the first time during the last week of 2025.
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There are indications the situation may grow even more dire. Fewer than 43% of adults were vaccinated at the end of last year, according to the CDC. The surging flu activity across the US is being driven largely by a new variant, dubbed the super flu. It is a mutation of the common H3N2 influenza strain, and shots that are now available appear to be a poor match for it.
“We’re far from a peak in the US,” said virologist Andy Pekosz from the Johns Hopkins Bloomberg School of Public Health. “We don’t know really how strong this virus is and how long it will be able to persist in the population.”
The variant has the ability to evade protection from the vaccine or a previous infection, said Pekosz, a professor of microbiology. That’s making a greater proportion of Americans susceptible to an infection and allowing the pathogen to spread quickly, he said.
It’s become a serious problem for children and teenagers. More than 8% of emergency department visits during the last week of the year were because of influenza, according to the CDC. That climbed to more than 20% of visits for kids 5 to 17 years old, and 18% for children under the age of 4, data from the public health agency showed.
Nine children have already died from the flu this season. Deaths are a lagging indicator, however, and increase as the season progresses. Last year, the US saw more than 280 pediatric deaths due to flu, in what was considered the deadliest non-pandemic season.
Influenza typically starts in the US Southeast before slowly spreading north and west. The highest levels of outpatient activity are still concentrated in the eastern US, and are starting to climb in states like California, Oregon and Washington. It’s still early in the flu season, which typically winds down by May.
Despite the mismatch between the shot and the virus this season, the vaccine is still the best way to protect against severe infection, hospitalization or death. Flu is a dynamic virus, and the shot that is available is well matched to other strains, Pekosz said.
“Even though it may not protect as well from infection, it gives you enough of an immune boost to protect you from that severe disease,” he said.
–With assistance from Tanaz Meghjani.
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