What is influenza?

What is influenza?sick-man-in-bed-the-flu

Influenza, commonly called the flu, is a respiratory disease that affects the nose, throat and lungs. It is caused by a virus that is easily passed from person to person.

  • Seasonal influenza is the annual influenza that affects people in Canada during the winter, between November and April.
  • Seasonal influenza viruses change slightly from year to year.
  • Various strains of influenza virus circulate throughout the world each year and new strains can emerge and spread.
  • Most healthy people are able to recover from influenza without severe complications.
  • As with other viral illnesses, antibiotics do not work against an influenza virus. Antiviral medications may be used for treatment or prevention of influenza.

Influenza lowers the body’s ability to fight other infections. It can lead to bacterial infections, such as pneumonia, and even death especially in the elderly, children (6–59 months), pregnant women, Aboriginal peoples, and people with chronic medical conditions.

How is influenza spread?

Influenza spreads rapidly among people.

  • The virus passes from person to person when an infected person coughs, sneezes or talks. Tiny drops of moisture (droplets) containing the virus can enter the eyes, nose or mouth of people nearby.
  • The virus can live on hands and is then passed to surfaces through touching. The virus can live on hard surfaces such as door handles, telephones, light switches, computer keyboards, countertops for up to 48 hours, and on soft surfaces like clothing for 8–10 hours.
  • Infection can happen when people touch any surface contaminated with the virus and then touch their own mouth, nose or eyes before washing their hands.
  • People usually develop symptoms of influenza within four days after becoming infected.
  • People are contagious for seven days after symptoms start.
  • Children, especially younger children, individuals with weakened immune systems and those with severe illness may be contagious for a longer period, i.e., up to 10 days .

Influenza symptoms

People develop symptoms of influenza from 1–4 days after becoming infected. They can pass on the virus from the day before they have the first symptoms until at least 5–7 days after the symptoms start.

Symptoms include:

  • Fever of 38 C (100.4 F) or higher that starts suddenly;
  • A dry cough that can last for weeks;
  • Headache;
  • An aching body especially in the lower back and legs;
  • Feeling very weak and tired.

Other symptoms can include:


  • Individuals younger than 5 years of age or those 65 years of age and older may not have a fever.
  • Fever usually goes down and the person starts to feel better in 3–5 days. However, exhaustion and cough can continue for several weeks.
  • Symptoms in babies may be hard to detect. For some babies, crying more than usual may be the only sign of illness.
  • Influenza symptoms are different from those of a cold or a stomach upset.

Influenza self-care

The influenza self-care section has information to help take care of yourself and others who have influenza.

If you have more questions, contact Health Link at 811.

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