Two new reports this week from the Centers for Disease Control and Prevention (CDC) provide more detail on the deadliest flu season for US children in more than a decade.
The reports, published yesterday in Morbidity and Mortality Weekly Report (MMWR), include data on the 280 US children who died during the 2024-25 flu season, along with information on 109 children who died from a rare and severe neurologic complication of flu during the season. The 280 pediatric flu deaths are the highest number reported in the United States since the 2009-10 H1N1 pandemic and the highest for a non-pandemic flu season since child deaths became nationally notifiable in 2004.
The reports add further information on what the CDC has previously described as a high-severity flu season.
Highest mortality rate seen in infants
In first report, researchers with the CDC's National Center for Immunization and Respiratory Diseases analyzed data from the Influenza-Associated Pediatric Mortality Surveillance System, which collects reports on pediatric flu deaths from state and local health departments. The analysis includes information on flu virus types, underlying medical conditions, vaccination status, and healthcare use during illness.
The 280 children who died with flu from September 29, 2024 to September 13, 2025, represent a national rate of 3.8 deaths per 1 million children. The median age at time of death was 7 years, and 61% of deaths occurred in children under the age of 9 years. The influenza-associated mortality rate was highest overall in infants under 6 months of age (11.1 per 1 million), higher among girls (4.5) than boys (3.1). Among racial and ethnic groups, Black children (5.8) had the highest mortality rate.
Influenza A viruses were associated with 240 deaths (86%) and influenza B viruses with 38 (14%). Of the 169 influenza A deaths with a known subtype, 95 (56%) were A(H1N1)pdm09 viruses, 73 (43%) were A(H3N2) viruses, and one (less than 1%) had both A(H1N1)pdm09 and A(H3N2) detected.
Among the 262 children with available medical histories, 148 (56%) had at least one reported underlying medical condition, with neurologic conditions the most frequently reported (93; 63%). Among the 218 children with available data on clinical complications before death, the most common complication was sepsis (108; 50%), followed by pneumonia (82; 38%), acute respiratory distress syndrome (60; 28%), seizures (53; 24%), and encephalopathy or encephalitis (40; 18%).
Overall, 112 (40%) of children were treated with flu antiviral medications, most commonly oseltamivir (104; 93%). Roughly half of the children who died had not been admitted to the hospital at the time of their death, with 61 (22%) deaths occurring outside of the hospital and 74 (27%) in the emergency department.
Of the 208 children with vaccine information available, 89% had not been fully vaccinated against flu.
The authors of the report say that while it's unclear why there were more pediatric deaths in the 2024-25 flu season than previous seasons, the best way to protect children from flu, particularly those with underlying conditions, is to get them vaccinated.
"All persons aged ≥6 months who do not have contraindications should receive an annual influenza vaccination to prevent influenza and its complications, including influenza-associated death," they wrote.
Influenza-associated encephalopathy
In the other MMWR report, researchers with the CDC and state and local health departments analyzed case reports on deaths among children from a severe and deadly form of influenza-associated encephalopathy (IAE) called acute necrotizing encephalopathy (ANE), which occurs when a virus (most commonly flu) triggers an immune response that leads to brain swelling, bleeding, and tissue death.
Children who survive ANE can experience lasting effects, including developmental delays, cognitive or behavioral challenges, and difficulty with movement or coordination.
Although there's no surveillance system in the United States for flu-related neurologic complications, the CDC requested the reports in January, after it was alerted to several deaths of children with influenza-associated ANE. Of the 192 reports that met CDC criteria, 109 were categorized as IAE, 37 (34%) of which were subcategorized as ANE.
Among the 109 patients with IAE, the median patient age was 5 years, 97 (89%) had influenza A, and 58 (55%) of 106 children with medical histories had no underlying medical conditions. Neurologic symptoms commenced a median of 2 days after illness onset. Of all IAE patients, 80 (74%) were admitted to the intensive care unit (ICU), 59 (54%) received mechanical ventilation, and 21 (19%) died.
Among the 37 ANE patients, the median patient age was 4 years, 34 (92%) had influenza A, and 18 (51%) of 35 children with available medical histories had no underlying conditions. All ANE patients were admitted to the ICU, 33 (89%) received mechanical ventilation, and 15 (41%) died.
Only 15 (16%) IAE and 4 (13%) ANE patients had received one or more doses of the 2024-25 flu vaccine more than 2 weeks before illness onset, while 86 (84%) of IAE and 31 (94%) of ANE patients received a flu antiviral.
The study authors say the findings are a reminder for parents and healthcare providers that all children are at risk for severe neurologic complications from flu.
"During influenza season, parents and caregivers of children with neurologic signs and symptoms (e.g., seizures, hallucinations, or altered level of consciousness) in conjunction with fever or respiratory symptoms should seek care urgently," they wrote. "Health care providers should consider IAE in children with recent or current febrile illness with encephalopathy, monitor these children for clinical deterioration, and initiate appropriate supportive care."
