The flu is a highly contagious illness caused by an influenza virus. The influenza virus causes infections of the nose, throat, and lungs. It spreads easily by coughing, sneezing, and direct contact with spit, phlegm or runny nose.


Flu symptoms appear 1 to 4 days after exposure to the virus. They generally include the sudden appearance of some or all the following:

  • fever
  • cough
  • muscle aches and pain
  • headache
  • chills
  • fatigue (tiredness)
  • loss of appetite
  • sore throat
  • runny or stuffy nose
  • diarrhea, nausea or vomiting (more common in children)


The influenza immunization is called the flu shot. It is important to get a flu shot every ‘flu season’, because the virus changes and each immunization is designed to address the changes.

Immunizations protect you as well as those around you by helping your immune system recognize and fight the flu. There are different ways an immunization can do this. Some introduce a weakened virus or an inactivated virus into the cells, while others create a copy of the virus or introduce an empty ‘shell’ without a virus inside it.

No matter how it works, the immunization itself will not cause the flu. The flu shot helps the body use its own immunity to prevent the flu.

People who should get the flu shot: Everyone older than 6 months should receive immunization when available.

People who should not get a flu shot are those who have

  • experienced anaphylactic reactions to previous influenza immunizations or
  • developed Guillain-Barré Syndrome (GBS) within 6 weeks of a previous immunization.