Viral pneumonia, including SARS-CoV-2 and influenza A virus (IAV), can culminate in acute respiratory distress syndrome (ARDS), a severe form of respiratory failure with high mortality. Uncontrolled local inflammatory response and impaired tissue repair are hallmarks of ARDS. However, lack of in-depth understanding of the immunopathology lead to limited identification of potential 'endotypes' who may benefit from individualized targeted therapies. Mucosal Associated Invariant T (MAIT) cells represent a peculiar lineage of T cells with a wide panel of effector functions. Thus, they emerge as potential key players and appealing targets in ARDS through their potent abilities to modulate immune response at barrier sites and promote tissue repair. Recent data from the investigators and others indicated that MAIT cells are highly activated in patients with Sars-Cov-2 and IAV ARDS, but the associated activation mechanisms and precise functions remain unknown. In this context, the investigators aim at investigating the implication and potential harnessing of MAIT cells in severe viral pneumonias and associated ARDS by with a dedicated clinical study. First, the investigators will perform a comprehensive and longitudinal phenotyping of immune response during viral pneumonia-induced ARDS, including MAIT cells, in blood -and airway compartment for mechanically ventilated patients. To provide more insight into specificity of virally induced pneumonia and ARDS, longitudinal phenotyping of immune response of patients with bacterial pneumonia, and control patients with unrelated ARDS (severe trauma, pancreatitis or major surgery) will also be performed.