Each type has many different strains, which tend to change each year. New strains are named by both type and place where they are found. For most healthy children and adults, flu is typically a moderately severe illness.
Most people recover within a week.
A complication called Reye Syndrome can occur if a child with flu takes any form of aspirin or salicylates. Flu is most serious for the elderly, people with chronic underlying illnesses such as cancer, emphysema or diabetes, or those with weak immune systems. Symptoms of the flu include fever, headache, stuffy head, muscle aches, general weakness, and congestion in the nose, throat, and lungs. Intestinal symptoms are uncommon. Fevers may rise as high as 104 degrees, but usually subside in two or three days.