Reports of Encephalopathy Among Children with Influenza-Associated Mortality - United States, 2010-11 Through 2024-25 Influenza Seasons

Abstract

In late January 2025, CDC received anecdotal reports of children with influenza-associated acute necrotizing encephalopathy (ANE), a severe form of influenza-associated encephalopathy or encephalitis (IAE), including several fatal cases. In response, CDC examined trends in the proportions of cases with IAE among influenza-associated pediatric deaths reported during the 2010-11 through 2024-25 influenza seasons, including demographic and clinical characteristics of identified cases. CDC contacted state health departments to ascertain whether any pediatric influenza-associated deaths with IAE reported this season also had a diagnosis of ANE. Among 1,840 pediatric influenza-associated deaths during the 2010-11 through 2024-25 influenza seasons, 166 (9%) had IAE, ranging from 0% (2020-21 season) to 14% (2011-12 season); preliminary data for the 2024-25 season (through February 8, 2025) indicate that nine of 68 (13%) had IAE. Across seasons, the median age of patients with fatal IAE was 6 years; 54% had no underlying medical conditions, and only 20% had received influenza vaccination. Because no dedicated national surveillance for IAE or ANE exists, it is unknown if the numbers of cases this season vary from expected numbers. Health care providers should consider IAE in children with acute febrile illness and neurologic signs or symptoms lasting >24 hours. Evaluation should include testing for influenza and other viruses and neuroimaging; clinical management should include early antiviral treatment for suspected or confirmed influenza and supportive critical care management as needed. Influenza vaccination is recommended for all eligible persons aged ≥6 months as long as influenza viruses are circulating.