What is influenza (the flu)?

The flu is a contagious respiratory illness caused by influenza viruses that infect the nose, throat and lungs. The flu can cause mild to severe illness, and, at times, can lead to death. The best way to prevent the flu is by getting a flu vaccine (flu shot) each year.

Signs and symptoms of the flu

People with flu symptoms often feel some of all of the following:

  • Fever or feeling feverish/chills
  • Cough
  • Sore throat
  • Runny or stuffy nose
  • Muscle or body aches
  • Headaches
  • Fatigue
  • Some people with flu symptoms may experience vomiting or diarrhea; this is more common with flu in children than adults

More information

How is flu spread?

It's believed that flu viruses spread mainly by droplets made when people with a flu cough, sneeze or talk. These droplets can land in the mouths or noses of people nearby. Less often, a person might also get flu by touching a surface or object that has flu virus on it and then touching their own mouth, eyes or nose. These are the most common ways the flu is spread.

How long is the flu contagious?

Most adults can infect others with the flu one day before symptoms develop and up to seven days after becoming sick. Even if a person shows no flu symptoms, they still may be able to spread the influenza virus.

Can the flu be prevented?

The first and most important step in preventing the flu is to get a flu vaccination (flu shot) every year. The CDC also recommends everyday preventive actions such as staying away from people who are sick with the flu, covering coughs and sneezes, and frequent hand washing to help slow the spread of germs that cause respiratory illnesses like the flu.