In a concerning update shared by the Centers for Disease Control and Prevention (CDC), 109 cases of Influenza-Associated Encephalopathy (IAE) have been identified in children under 18 years of age during the 2024-25 influenza season. Of these cases, approximately one third were classified as Acute Necrotizing Encephalopathy (ANE), highlighting a troubling trend in severe influenza-related neurological complications among pediatric patients.
The CDC’s call for case reports on IAE was initiated on February 28, 2025, utilizing the Epidemic Information Exchange (Epi-X). Clinicians and public health departments were prompted to report cases that met the CDC’s IAE surveillance criteria. Case report forms were completed by healthcare providers and partners within CDC-sponsored surveillance networks, ensuring thorough data collection for cases that fit the defined parameters.
A crucial aspect of this data collection involved the review of neuroimaging findings and discharge diagnoses by trained physicians. This review determined whether cases were classified as IAE or influenza-associated neurologic disease. Out of the 109 IAE cases, 37 (or 34%) were specifically categorized as ANE, while the remaining cases fell into other IAE categories or were classified as influenza-associated neurologic diseases.
Importantly, cases were excluded from consideration if there was co-detection of a neuroinvasive pathogen alongside influenza. This ensured that the data retained focus on the impact of influenza alone in the context of neurological complications.
The demographics and clinical characteristics of these cases revealed alarming patterns. The median age of patients diagnosed with IAE was found to be 5 years. The gender distribution showed a slight majority of females (46%) and a notable proportion of non-Hispanic White patients (52%). The majority were infected with the influenza A virus, which accounted for 89% of the cases, and of the cases where subtype data was available, most were attributed to the A(H1N1)pdm09 or A(H3N2) strains.
Approximately 55% of the children with IAE were previously healthy, showing that even those without underlying medical conditions could develop severe complications.
Common initial symptoms included altered mental status (reported in 88% of cases), respiratory symptoms (87%), and fever (85%). Notably, seizures were recorded in 87% of patients with ANE upon admission, compared to 45% of patients with other IAE types. This indicates a significant difference in symptomology between the classifications, signaling the potential severity of ANE.
Neurological symptoms typically manifested a median of two days after the onset of influenza symptoms, prompting early medical evaluations for these children. Neuroimaging studies were conducted for 94% of IAE patients, revealing abnormal findings in 97% of those diagnosed with ANE as opposed to 49% in other IAE patients.
Treatment responses varied, but overall, 84% of IAE patients received antiviral treatment, primarily oseltamivir. Alarmingly, treatment began a median of three days after symptom onset, which raises questions about the timeliness of medical responses for these cases. Additionally, 74% of IAE patients required admission to an intensive care unit (ICU), and invasive mechanical ventilation was necessary for 54% of them. Tragically, the mortality rate among these patients reached 19%, indicating the severe nature of the illness.
Among survivors, follow-up evaluations at discharge revealed that 47% had not returned to their neurological baseline, underscoring the potential long-term impacts of IAE. The evaluation of seasonal influenza vaccination revealed a concerning statistic: only 16% of patients eligible for the vaccine had received the 2024-25 seasonal influenza vaccine at least 14 days prior to their illness onset.
A closer look at the ANE subcategory revealed even more worrying outcomes. The median age of these 37 patients was slightly lower, at 4 years, with comparable statistics regarding pre-existing health conditions. Only 13% of ANE patients had received the seasonal influenza vaccination prior to illness, and treatment regimens indicated the severity of their cases, with 94% receiving antiviral medications and high percentages also receiving systemic corticosteroids, intravenous immunoglobulin, and other immunomodulators.
The situation regarding ANE showed that every patient was admitted to an ICU, and 89% needed invasive mechanical ventilation. The mortality rate for ANE patients reached 41%, and survivors faced prolonged hospitalization, averaging 30 days before discharge. Alarmingly, it was noted that those who succumbed to the illness did so after a median hospitalization of merely four days, highlighting the rapid progression of the disease.
In discussing these findings, experts point out the significance of the epidemiological trends in influenza-associated complications. The CDC’s report indicates an imperative public health message about the potential dangers influenza poses to children, even those who are otherwise healthy. The urgent need for vaccination and prompt treatment options is clear.
The findings from the CDC’s data, while concerning, also reinforce ongoing discussions in the medical community regarding the critical need for annual influenza vaccination in children aged 6 months and older. The decline in vaccination rates over recent years raises alarm bells, especially in light of these severe cases of IAE and ANE.
As flu seasons continue to yield cases of this nature, emphasis on vaccination can drastically reduce the risks associated with influenza illness and its complications. Early antiviral treatment is crucial for children suspected of having influenza, particularly for those at elevated risk of developing severe symptoms.
Despite the introduction of rigorous vaccination recommendations since 2010, adherence appears to falter. Given the current trends in IAE and ANE cases, public health messaging surrounding influenza vaccination needs to be stronger and more compelling.
With these insights, the CDC acknowledges limitations in their findings, emphasizing the need for further awareness and education on IAE. The cases reported are a convenience sample, which may not represent the full scope of IAE incidents across the United States. Furthermore, the absence of standardized diagnostic criteria for diagnosing IAE contributes to the likelihood that many cases go unreported or misclassified.
In their concluding remarks, the CDC outlines plans to integrate surveillance for IAE and ANE into existing monitoring systems for the subsequent influenza season. This initiative aims to bolster understanding of these severe complications and hopefully mitigate their occurrence in the future.
Public health experts recommend that healthcare providers remain vigilant for signs and symptoms indicative of IAE in children presenting with recent febrile illness coupled with neurological alterations. The call to action is clear: early intervention, robust monitoring, and adherence to vaccination protocols may be pivotal in preventing severe outcomes associated with influenza.
During the flu season, parents and caregivers must stay informed and act promptly when children exhibit concerning symptoms, ensuring that they receive the care necessary to avert potentially life-threatening complications.
The CDC’s ongoing work to track and analyze IAE incidences sets the groundwork for future public health initiatives that aim to protect vulnerable populations from influenza’s devastating potential.
image source from：cdc
