Final answer:
The most common viruses causing pneumonia include Influenza virus types A and B, Respiratory syncytial virus, Parainfluenza virus, Adenovirus, and SARS coronavirus, with higher risks in vulnerable populations like children and the elderly.
Step-by-step explanation:
The most common viruses that cause pneumonia are the Influenza virus types A and B, Respiratory syncytial virus (RSV), Parainfluenza virus, Adenovirus, and SARS coronavirus.
These viruses can be particularly severe in children and the elderly. Pneumonia often develops following an upper respiratory tract infection, such as the common cold or flu, and is more likely to occur in individuals with other lung diseases, a history of smoking, or a weakened immune system.