All children and adolescents < 17 years of age fulfilling the following criteria for severe paediatric influenza-associated infections were included: i) laboratory-confirmed influenza (antigen test or PCR or virus isolate) within one week before or after start of influenza symptoms, and ii) hospitalisation to a PICU with need for intratracheal/CPAP ventilation and/or one of the following diagnoses: encephalitis/encephalopathy, bronchitis/bronchiolitis, complicated febrile seizure, acute respiratory distress syndrome (ARDS), influenza-associated pneumonia, secondary bacterial pneumonia, status asthmaticus, sepsis, myocarditis, apnoea/bradycardia, or iii) influenza-associated death.