Clinical Trial Evaluating the Efficacy and Safety of Dexamethasone Compared to Placebo in Patients With Severe Influenza

Inclusion Criteria: 1. Aged ≥ 18 years. 2. Diagnosis of influenza A or B virus infection by antigen or RT-PCR (local laboratory) at the time of entry or at 48 hours prior to randomization in respiratory specimens (nasopharyngeal swab or bronchoalveolar lavage). 3. Hospitalized patients with an estimated hospital stay of more than 24 hours. 4. In previous treatment or concomitant start of treatment with oseltamivir. 5. For women of childbearing age, use of contraceptive methods until day 30 after completion of treatment. 6. Signed informed consent. Exclusion Criteria: * 1\. Patients with bronchial hyperresponsiveness that requires systemic corticosteroids for more than 24 hours. 2\. Pre-inclusion treatment with corticosteroids for more than 24 hours at a dose equal to or higher than 1 mg/kg methyl-prednisolone (0.2 mg/kg dexamethasone or 1.25 mg/kg prednisone). 3\. Inability to administer oral oseltamivir. 4. Patients on ECMO (extracorporeal membrane oxygenation). 5. Pre-existing condition or use of medication that, in the opinion of the local investigator, may pose a risk for the administration of corticosteroids. 6\. Patients with severe comorbidity with life expectancy of less than six months in the opinion of the investigator. 7\. Patients co-infected with SARS-CoV-2 or RSV.