Almost a dozen children with the flu have contracted a rare brain disorder that causes seizures, delirium and death.
The CDC reported that of 68 children who have died of the flu during the 2024-2025 season, nine had a condition called influenza-associated encephalopathy or encephalitis (IAE), including four who had a more severe subtype called acute necrotizing encephalopathy (ANE).
The CDC didn’t reveal any details about the children aside from they were all under five years old and only two were vaccinated.
ANE occurs when the body’s immune system overreacts to a common virus, like the flu. It causes widespread inflammation and tissue damage throughout the body, including the brain.
This lets toxins and bacteria enter the brain and kill tissue. Over time, the brain swells and cells die.
IAE is relatively rare, with studies in past flu seasons showing roughly nine percent of children who died of flu had it. ANE, a distinct form of IAE, is even less common, with just a few hundred documented cases in medical literature.
The US is experiencing one of its worst flu seasons. Cases have hit a 15-year high and 430,000 Americans have been hospitalized while 19,000 have died from the flu, including 86 children.
Just over 45 percent of American children have gotten a flu shot this season, down from about 50 percent last year, meaning roughly 40million children are at risk of a potentially severe flu infection.
The CDC reported that, as of February 5, 2025, of 68 flu-related pediatric deaths during the 2024-2025 season, nine involved influenza-associated encephalopathy or encephalitis, including four cases of the fatal form, acute necrotizing encephalopathy (stock photo)
This map tracks visits for respiratory illnesses with fever, cough, or sore throat (ILI), which may not be flu. As of Week 7 of the 2024-2025 flu season, New York City, Alaska, and Puerto Rico have ‘Very High’ ILI activity, while other areas show ‘Moderate’ to ‘Low’ levels. Some regions lack data
It’s not clear why the US flu outbreak is so widespread, but researchers suspect an ‘immunity gap’ still exists because people were less exposed to influenza during the pandemic because of masking and social distancing requirements.
There are also two strains of influenza circulating simultaneously. This level of unpredictability may have made this year’s flu vaccine less effective against the virus than in previous years.
The vaccine introduces the immune system to an inactive form of the virus to learn how to fight it off without the body actually getting sick.
Without that vaccine as a primer, the real virus can cause an excessive immune response that kicks off what scientists call a cytokine storm made up of inflammatory molecules that damage healthy tissues.
When the body becomes inflamed, the protective layer of tightly packed cells lining blood vessels in the brain become permeable, allowing those cytokines, virus particles, bacteria, immune cells, and other damaging molecules to enter the brain, which starts to swell.
The attack on the brain, swelling that restricts blood flow, and inflammation wreak havoc on brain cells, which can lead to confusion, loss of consciousness, seizures, and in some cases, brain death.
ANE is an exceedingly rare complication of IAE, with only a few hundred documented cases worldwide ever.
Both involve inflammation of the brain, but ANE is a more specific and severe form.
The graph from the National Syndromic Surveillance System (NSSP) shows the percentage of emergency department (ED) visits with an influenza diagnosis across the 2023-2024 and 2024-2025 seasons
The nine patients who died ranged in age from two to 10. Just over half were girls.
Two of the children with ANE had received a flu vaccine more than two weeks before they got sick, while the other two with the rare subtype had not.
The report did not say whether the other seven children had been vaccinated.
Two of the children with ANE were treated with antiviral medications and two had seizures. The report did not say if those were the same children, however.
All four children needed to be hooked up to ventilators to breathe.
Pediatric flu deaths involving IAE have fluctuated over the past 15 flu seasons without a clear increasing or decreasing trend.
Between the 2010 – 2011 and 2024 – 2025 seasons, the percentage of flu deaths linked to IAE has ranged from four percent to 14 percent.
Most seasons fall between eight percent and 10 percent. The highest recorded percentage was 14 percent in 2011–2012, while the lowest (excluding the 2020–2021 season during the pandemic) was four percent in 2013 – 2014.
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The 13 percent of deaths attributed to IAE this season is slightly above the long-term average but within the historical range.
The CDC tracked these cases through its national pediatric influenza-associated mortality surveillance system, which monitors deaths related to flu in children.
There is no systemic way of reporting deaths due to IAE, but CDC researchers noticed 13 percent of the children who died from flu-related complications also had the rare brain disorder.
The agency has tried to enhance surveillance by posting a national call for reports of potential IAE cases through its information exchange database. This database allows healthcare providers and public health officials to report cases they find.
There are no guidelines supported by evidence for treating IAE, but several treatments have been tried. These include high-dose steroids, plasma exchange, cooling therapies to lower body temperature, and immunotherapy treatments.
The CDC recommends people six months of age and older get a flu shot. The shot contains an inactivated version of the virus, which helps the body develop immunity to it without getting sick.
Although the vaccine may not guarantee complete protection against sickness, as flu viruses can change, it significantly reduces the risk of getting severely ill and needing to be hospitalized. Being vaccinated often means milder symptoms and faster recovery.
