Effectiveness of oseltamivir in reduction of complications and 30-day mortality in severe seasonal influenza infection

•High-quality evidence for the effectiveness of oseltamivir in seasonal influenza is lacking.•Propensity score matching improves the quality of influenza treatment effect study.•Oseltamivir within 48 h of admission in hospitalized influenza patients reduces 30-day mortality.•Oseltamivir within 48 h of admission in hospitalized influenza patients reduces mortality or intensive care unit admission.•CURB-65 score predicts 30-day mortality in hospitalized influenza patients.