Influenza-associated neurologic complications in children from an H3N2 outbreak in Shenzhen, China during COVID-19 lockdown

•H3N2-associated neurologic complications mainly occur early in the disease course.•Unvaccinated patients infected with H3N2 may be at risk for neurologic complications.•The development of encephalopathy/encephalitis likely involves alanine aminotransferase. To identify the characteristics of influenza-associated neurologic complications (INCs) in children from a recent H3N2 outbreak in Shenzhen, China during COVID-19 lockdown. A retrospective cohort study of INCs in children hospitalized with H3N2 infection was conducted. From June 01, 2022 to July 01, 2022, 513 children with H3N2 infection were hospitalized and 97 developed INCs. Of the 18 patients with encephalopathy/encephalitis, 13 were previously healthy. Three developed acute necrotizing encephalopathy and two died. Of the 63 patients with febrile seizures, 55 (87%) had simple febrile seizures. Of the 14 patients with an exacerbation of seizure with underlying epilepsy, the seizure symptoms occurred mostly within 24 hours of disease onset (13/14). The comparison of the three groups (encephalopathy/encephalitis, febrile seizure and exacerbation of seizure with underlying epilepsy) reported no significant differences in sex, pre-existing neurologic diseases, vaccination rate, white blood cell count, C-reactive protein, procalcitonin, blood glucose, lactic acid, or duration of fever. The influenza vaccination rates were generally low (22% vs 32% vs 21%). Patients with encephalopathy/encephalitis had a higher rate of elevated alanine aminotransferase (28% vs 3% vs 0, P = 0.005). H3N2-related neurologic complications in children mainly occur early in the disease course. Most patients were previously healthy and unvaccinated against influenza. Elevated alanine aminotransferase is more common in encephalopathy/encephalitis.