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Influenza, commonly known as the flu, is a viral respiratory infection caused by the influenza viruses. It can affect your entire respiratory system—nose, throat and lungs.1

The flu is very contagious and can spread easily. The viruses usually spread through droplets that travel through the air when someone with the flu coughs or sneezes. These droplets can be inhaled by anyone who happens to be nearby or can be picked up by touching a surface that has the germs, like a desk, door handle or keyboard—and then transferred by touching your mouth, eyes or nose.4

Because flu viruses change every year, researchers worldwide monitor the 3 or 4 strains that are most likely to infect the most people. The researchers then create a seasonal flu vaccine to best meet the needs of the current cold and flu season.2

Flu Symptoms

The flu can range from mild to severe—and symptoms usually develop quickly.4 In fact, one of the main differences between a cold and the flu is that the flu usually comes on fast. Even though a cold and the flu share a lot of the same symptoms, people with the flu will usually feel a lot worse.

An icon of a thermometer


An icon of a person’s head indicating cold temperatures (with a snowflake) and sweat (water drops on the head)

Chills, cold sweats and shivers

An icon of a person indicating body ache areas

Aching joints and limbs

An icon of a person’s head, with “Z”s in it, indicating tiredness

Feeling tired, exhausted, fatigued

An icon of a person’s mouth indicating coughing (three lines projecting outwards from the lips)

A cough

An icon of a person’s head and neck area highlighting the throat

Sore throat

An icon of a person’s nose & mouth area, indicating a runny nose with a water drop icon underneath the nose

Runny or stuffy nose

An icon of a person’s head highlighting a circular area on top of the skull


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