Overview

Influenza is a viral infection that attacks your respiratory system — your nose, throat and lungs. Influenza is commonly called the flu, but it's not the same as stomach "flu" viruses that cause diarrhea and vomiting.

For most people, the flu 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 age 5, and especially those under 6 months
• Adults older than age 65
• Residents of nursing homes and other long-term care facilities
• Pregnant women and women up to two weeks after giving birth
• People with weakened immune systems
• Native Americans
• People who have chronic illnesses, such as asthma, heart disease, kidney disease, liver disease and diabetes
• People who are very obese, with a body mass index (BMI) of 40 or higher

Though the annual influenza vaccine isn't 100% effective, it's still your best defense against the flu.