Objective: To identify the characteristics of influenza-associated neurologic complications (INC) in children from a recent H3N2 outbreak in Shenzhen, China during COVID-19 lockdown.

Methods: A retrospective cohort study of INC in children hospitalized with H3N2 infection was conducted.

Results: From June 1, 2022 to July 1, 2022, 513 children with H3N2 infection were hospitalized and 97 developed INC. Of 18 patients with encephalopathy/encephalitis, 13 were previously healthy. Three developed acute necrotizing encephalopathy and two died. Of 63 patients with febrile seizures, 55 (87%) had simple febrile seizures. Of 14 patients with exacerbation of seizure with underlying epilepsy (ESUE), seizure symptoms occurred mostly within 24 hours of disease onset (13/14). Comparison of 3 groups (encephalopathy/encephalitis, febrile seizure and ESUE) reported no significant differences in sex, preexisting neurologic diseases, vaccination rate, white blood cell count, C-reactive protein, procalcitonin, blood glucose, lactic acid, or duration of fever. 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).

Conclusions: H3N2-related neurologic complications in children mainly occur early in the disease course. Most patients are previously healthy and unvaccinated against influenza. Elevated alanine aminotransferase is more common in encephalopathy/encephalitis.