**Phase 2 Study of Inhaled SNG001 for Respiratory Viral Infection** This study tests a new treatment called **SNG001** for people with severe lung infections caused by viruses, like the flu or COVID-19. Some patients need a machine to help them breathe, called **mechanical ventilation**. The study hopes to see if SNG001 can help patients get better faster and lower the risk of death compared to usual treatments. The trial has **two parts**. In **Part 1**, patients aged 50 and older will receive SNG001 or a fake treatment (placebo) once a day for up to 14 days while in the hospital. This part checks if SNG001 is safe. In **Part 2**, the focus is on how well SNG001 works, involving patients aged 18 to 50 with immune system issues and those over 50. **Key Points:** - Duration: Up to 14 days in the hospital. - Participants: Some will receive SNG001, others a placebo. - Risks: Usual risks of hospital care and testing new treatment. **Note:** Patients must meet specific medical criteria to join and cannot have certain conditions.