About 50 percent of pneumonia cases are caused by viruses, particularly those viruses that cause upper respiratory infections, such as the viruses that cause influenza, adenoviruses, and rhinoviruses. Most cases of viral pneumonia are mild and resolve spontaneously without specific treatment.

 One exception is severe acute respiratory syndrome (SARS), a type of viral pneumonia. SARS typically begins with a fever of 38.0°C (100.4°F) or more, chills, headache, and malaise. Two to seven days later some people develop a dry cough and difficulty breathing. For these people SARS can cause death.