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 stomach "flu" viruses that cause diarrhea and vomiting.
For most people, influenza resolves on its own. But sometimes, influenza and its complications can be deadly. People at higher risk of developing flu complications include:
Young children under 5, and especially those under 2 years
Adults older than 65
Residents of nursing homes and other long-term care facilities
Pregnant women and women up to two weeks postpartum
People with weakened immune systems
People who have chronic illnesses, such as asthma, heart disease, kidney disease and diabetes
People who are very obese, with a body mass index (BMI) of 40 or higher
Your best defense against influenza is to receive an annual vaccination.