Influenza is a viral infection that attacks your respiratory system — your nose, throat and lungs. Influenza, commonly called the flu, is not the same as the stomach "flu" viruses that cause diarrhea and vomiting.
Influenza and its complications can be deadly. People at higher risk of developing flu complications include:
Young children
Adults older than 65
Pregnant women
People with weakened immune systems
People who have chronic illnesses
Your best defense against influenza is to receive an annual vaccination.