Compared with other respiratory infections, like the common cold, the flu can cause severe illness and lead to serious, and life-threatening complications in all age groups. Typical flu symptoms include fever, dry cough, sore throat, runny or stuffy nose, as well as headache, muscle aches, and extreme fatigue. Children may experience gastro-intestinal problems like nausea, vomiting and diarrhea, but such symptoms are not common in adults. Although the term 'stomach flu' is sometimes used to describe GI illnesses, this is caused by other organisms and is not related to 'true' flu. The flu is merely a nuisance.
Flu vaccine causes the flu.
The flu vaccine is not very effective. However, flu vaccine only provides protection against influenza. People who have received flu vaccine may subsequently develop a respiratory illness that is due to another virus, but is mistaken for flu. In addition, the vaccine is not 100 percent effective. Studies of healthy young adults have shown flu vaccine to be 70 percent to 90 percent effective in preventing illness.