"What is the flu?"

The flu is a contagious respiratory illness caused by the influenza virus. It can cause illness ranging from mild to severe, and sometimes leading to hospitalization or death. Most people who get the flu will recover in a few days to less than two weeks. The best way to prevent the flu is by getting a flu vaccination.


People who have the flu often feel some or all of the following symptoms:

  • Fatigue (very tired)
  • Muscle or body aches
  • Cough
  • Headaches
  • Sore throat
  • Fever
  • Runny or stuffy nose
  • Vomiting and diarrhea (more common in children than adults)

How is it spread?

The flu is primarily spread from person to person. Tiny droplets are released when an infected person coughs or sneezes. The droplets land in the mouths or noses of people close by. Occasionally people may become infected by touching something with the virus on it and then touching their eyes, nose, or mouth.

Is it contagious?

Yes. An infected individual may pass the flu to someone else before they realize they are sick. If possible, stay home when you are sick to prevent transmission of the illness. Most healthy adults may be able to infect others beginning one day before symptoms develop and up to five to seven days after becoming sick. Young children and those with a weakened immune system might be able to infect others for an even longer time.

How severe is the flu?

Severity of the flu is unpredictable and can vary from one season to the next, from person to person. The severity of a particular flu season will vary depending on a number of factors, including: the type of flu viruses spreading, how much and when the flu vaccine is available, how many people get vaccinated, and how well the flu vaccine is matched to flu viruses that are causing illness.

Certain people are more at risk for complications of the flu. Older adults, young children, pregnant women, and people with certain health conditions (e.g., asthma, diabetes, and heart disease) are more likely to suffer complications such as pneumonia, ear infections, sinus infections, dehydration, and worsening of chronic medical conditions.


In addition to getting the flu vaccine, practicing healthy habits can also protect you from getting sick. Frequent hand washing, avoiding close contact with people who are sick, avoiding touching your eyes, mouth, or nose, getting plenty of sleep, managing stress, and drinking plenty of fluids are all good strategies.

Last reviewed/updated: April 27, 2015