While a rhinovirus (a cold) is a minor respiratory illness that usually just inconveniences us, true influenza (the flu) is a serious respiratory illness.
Flu symptoms start one to four days after the virus enters the body. In adults, the flu is contagious for one day before symptoms occur and for three to seven days (as many as ten days in children) after the first symptoms appear.
Unlike a common cold, influenza causes high fevers, and severe headaches and body aches. The cough of influenza is hacking and severe compared to the cough associated with colds. People with colds commonly experience sore throats, sneezing, and stuffy noses, while people with influenza usually experience fatigue, weakness and exhaustion.
Complications of common colds include sinus infections and earaches, while complications of influenza are bronchitis and life-threatening pneumonia.