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, headache, muscle aches, and extreme fatigue. Children may experience gastrointestinal problems like nausea, vomiting, and diarrhea but such symptoms are not common in adults.
Flu vaccine causes the flu.
The licensed flu vaccine used in the United States, which is made from inactivated or killed influenza viruses, cannot cause influenza infection and does not cause influenza illness. Flu vaccine is not very effective. When the vaccine viruses and circulating viruses are well matched, vaccine can be 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.