Influenza is a common cause of pneumonia, especially among younger children, the elderly, pregnant women, or those with certain chronic health conditions or who live in a nursing home. Most cases of flu never lead to pneumonia, but those that do tend to be more severe and deadly. Pneumonia is the most common complication of the flu – and perhaps one of the most serious. ... Influenza never turns into pneumonia, but predisposes a person to developing the illness. Knowing the symptoms of both influenza and pneumonia are important, but can be difficult since they often share the same signs.