What is Influenza (Flu)?

Influenza, also known as the flu, is a contagious respiratory illness caused by specific viruses that infect the nose, throat, and sometimes the lungs.

This flu virus can cause mild to severe illness. At times, the flu can even lead to death.


Flu signs and symptoms often come on suddenly. People sick with the flu usually feel some or all of these well-known symptoms:

  • Fever or feeling feverish
  • Chills
  • Cough
  • Sore throat
  • Runny or stuffy nose
  • Muscle and/or body aches
  • Headaches
  • Fatigue (tiredness)

Occasionally, people with the flu may experience vomiting and/or diarrhea. While adults can experience these symptoms, vomiting and diarrhea with the flu is typically more common in children.

How Flu Spreads

Most experts believe that flu viruses spread primarily through tiny droplets made when people with the flu cough, sneeze, or talk. These droplets can land in the mouths or noses of people who are nearby. Less frequently, people could get the flu by touching a surface or object that has the flu virus on it and then touching their mouths, noses, or eyes afterward.

Who Should Get the Flu Vaccine

Anyone who is six months or older is recommended to get an annual flu vaccine, unless otherwise indicated by a doctor. The flu vaccine is especially important for individuals who are at higher risk, such as those with compromised immune systems or those aged 65 years and older.

Note, the information on this page is sourced from the CDC as of April 2023. For the latest information on influenza, please reference the CDC’s Influenza page here.