A bad year Doctors report upticks in severe brain dysfunction among kids with flu CDC data is limited but hints it could be one of the more severe seasons. Beth Mole Feb 27, 2025 1:00 pm | 12 Credit: Getty | Rebecca Nelson Credit: Getty | Rebecca Nelson Story textSizeSmallStandardLargeWidth *StandardWideLinksStandardOrange* Subscribers only Learn moreDoctors around the US have anecdotally reported an uptick of children critically ill with the flu developing severe, life-threatening neurological complications, which can be marked by seizures, delirium, hallucinations, decreased consciousness, lethargy, personality changes, and abnormalities in brain imaging.It's long been known that the seasonal flu can cause such devastating complications in some children, many with no underlying medical conditions. But doctors have begun to suspect that this year's flu seasonthe most severe in over 15 yearshas taken a yet darker turn for children. On February 14, for instance, health officials in Massachusetts released an advisory for clinicians to be on alert for neurological complications in pediatric flu patients after detecting a "possible increase."With the anecdata coming in, the Centers for Disease Control and Prevention analyzed all the data it has on neurological complications from flu this year and seasons dating back to 2010. Unfortunately, existing surveillance systems for flu do not capture neurological complications in pediatric cases overallbut they do capture such detailed clinical data when a child dies of flu.An analysis of that data, published today in the CDC's Morbidity and Mortality Weekly Report, can't definitively say that this year is out of the norm. For one thing, the flu season is not yet over. But the data so far does suggest it may be one of the more severe seasons in the last 15 years.Specifically, the CDC received reports of a severe neurological complication called influenza-associated acute necrotizing encephalopathy (ANE). ANE is a severe form of the more general category of influenza-associated encephalopathy or encephalitis (IAE), meaning brain dysfunction or inflammation from the flu.When a child dies of the flu, clinicians are required to fill out a standardized case report form from the CDC, which collects a large variety of data, including complications. Encephalopathy or encephalitis are included as a checkbox on the form.Between 2010 and February 8, 2025, 1,840 children died of the flu. Of those, 166 had IAE checked off as a complication. IAE was most prevalent in children aged 2 to 4 but affected children in all age groups under 18. More than half of the cases (54 percent) had no underlying medical conditions, and most (80 percent) were unvaccinated against the flu.Uncertain trendsMost of the cases (72 percent) were from an influenza type A strain rather than the generally less common type B. Among 73 cases with influenza A subtyping data, H1N1 was the most common virus strain (56 percent), with the remainder being H3N2. So far this flu season, H1N1 and H3N2 are circulating at about equal proportions.CDC scientists then broke out the data by year, finding a range of 0 percent of deaths with IAE (in the 20202021 flu season) to 14 percent of deaths with IAE (20112012). So far in this flu season, there have been 68 pediatric deaths, nine of which (13 percent) were with IAE. That puts this flu season as the second worst for IAE-caused pediatric flu deaths. But again, the data is preliminary as the flu season is still ongoing, and there can be lags in reporting.Whether ANE is occurring more frequently than in previous years is yet more uncertain, given that it's not a complication systematically reported on the standardized case reports for flu deaths. ANE is a severe type of IAE that is diagnosed based on a specific pattern of brain lesions seen on computed tomography (CT scans) or magnetic resonance imaging (MRIs).The CDC called the health departments of the states where the nine fatal cases with IAE had been reported to ask if the children had ANE specifically. Of the nine IAE fatalities, four had the more severe ANE. All four of the deaths were in children younger than age 5. Only one child had underlying health conditions. Two had been vaccinated against the flu. All of the children were infected with H1N1.Given the data limitations, "it is currently not known whether these reported cases vary from expected numbers," the CDC researchers conclude. The CDC noted that Japan does systematically collect data on encephalitis and encephalopathy generally, as well as IAE specifically. Between 2010 and 2015, 74 percent of all IAE cases were in people under the age of 18. Of those IAE cases in children and teens, 8 percent were fatal.While this year's flu season is still going, the CDC researchers called for enhanced surveillance to try to capture data on IAE in non-fatal cases. The researchers also emphasized the importance of vaccination, which is known to reduce the risk of the flu and its complications.Beth MoleSenior Health ReporterBeth MoleSenior Health Reporter Beth is Ars Technicas Senior Health Reporter. Beth has a Ph.D. in microbiology from the University of North Carolina at Chapel Hill and attended the Science Communication program at the University of California, Santa Cruz. She specializes in covering infectious diseases, public health, and microbes. 12 Comments