I can explain why viruses like SARS-CoV-2 cause pneumonia. When the virus enters the respiratory system, it invades the cells lining the lungs, hijacking their machinery to replicate. This damages the lung tissue and triggers an intense immune response. The immune system sends white blood cells and inflammatory molecules to fight the infection, but this can lead to fluid buildup and swelling in the lungs. The combination of viral damage and the body's own immune response makes it harder for oxygen to pass into the bloodstream, leading to the symptoms of pneumonia. Severe cases can result in acute respiratory distress syndrome (ARDS), where the lungs struggle to supply enough oxygen to the body.