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Influenza, often called the "flu", is an infection of the upper airway (the nose and throat), caused by an influenza virus.


The influenza virus is a highly changeable virus. 

A person with influenza is at risk of other infections, including viral or bacterial pneumonia which is an infection of the lungs.

Information for Health Care Professionals

Influenza, often called the 'flu', is an infection of the upper airway (e.g. nose and throat) caused by an influenza virus.

A person with influenza is also at risk of other infections. These include viral or bacterial pneumonia, an infection of the lungs. The risk of complications is greater for seniors 65 years and older, very young children, and people who have lung or heart diseases, certain chronic health problems, or weakened immune systems.


Influenza symptoms can include fever, headache, muscle pain, runny nose, sore throat, extreme tiredness, and cough. Although colds and other viruses may cause similar symptoms, those due to the influenza virus tend to be worse.

Symptoms can begin about one to four days (on average two days) after a person is first exposed to the influenza virus. Fever and other symptoms can usually last 7 to 10 days, with the cough and weakness lasting up to two more weeks.

In children, gastrointestinal  symptoms such as nausea, vomiting and diarrhea may accompany the respiratory phase


How is influenza spread?

Influenza spreads easily from person to person through breathing, coughing, and sneezing. The virus can also spread when a person touches tiny droplets from coughs, or sneezes on another person or on an object, and then touches his or her own mouth or nose before washing his or her hands.

An adult can spread the virus from about one day before to five days after symptoms start. Children can spread the virus up to 21 days after symptoms start.


Influenza can lead to pneumonia and respiratory failure, and more complications in persons with chronic diseases.

Some groups of people, such as very young children and the elderly, may be especially vulnerable.

Is it influenza or a cold?

The following table can help you determine whether you have influenza or a cold.

Symptoms Cold Influenza (the flu)
feverrareusual, sudden onset 39º-40ºC, lasts 3 to 4 days. Usually accompanied by other symptoms
headacherareusual, can be severe
aches and painssometimes mildusual, often severe
fatigue and weaknesssometimes mildusual, may last 2-3 weeks or more
extreme fatigueunusualusual, early onset, can be severe
runny, stuffy nosecommonsometimes
sore throatcommonsometimes
chest discomfort, coughingsometimes mild to moderateusual, can be severe
complicationscan lead to sinus congestion or earachecan lead to pneumonia and respiratory failure, and more complications in persons with chronic diseases
preventionfrequent hand-washingyearly influenza vaccine and frequent hand-washing
treatmentno specific treatment is available; symptom relief onlyanti-viral drugs by prescription, which can reduce symptoms

Home treatment

If you do get sick with the flu, home treatment can help to ease symptoms. Home treatment may include:

  • Get plenty of rest. Bed rest will also help you avoid spreading the virus to others.
  • Drink plenty of extra fluids to replace those lost from fever.
  • Avoid smoking/vaping nicotine products such as cigarettes, and breathing other people's smoke.
  • Breathe moist air from a hot shower or from a sink filled with hot water to help clear a stuffy nose.
  • Anti-influenza drugs or antivirals are available by prescription, but these must be started early. They will shorten symptoms by about three days if given within 12 hours, and by about 1.5 days if given within two days of the start of symptoms.
  • Over-the-counter medications can help relieve symptoms such as pain and fever. These are not recommended for children under six years of age. Non-prescription flu remedies are also available at the pharmacy.


When should I see a doctor?

If you do not start to feel better in a few days or your symptoms get worse, you should see a doctor. Call a doctor if you get sick and you have the following health concerns:

  • Heart or lung disease
  • Any chronic health concern that requires regular medical attention
  • An immune system weakened by disease or medical treatment, or
  • You are frail or at risk of serious illness or complications

You can reduce the risk of catching influenza or spreading it to others, by washing your hands regularly, eating well, exercising, and getting the influenza vaccine. 


Influenza vaccine, also known as the "flu shot", may help prevent you from getting sick with influenza or from spreading it to others. In BC, the vaccine is available in October or early November. If you choose to get the influenza vaccine, it is best to try to get it by the end of November to allow your body enough time - about two weeks - to build immunity before the influenza season starts. However, the vaccine may be given at any time during the season.

SOURCE: Influenza ( )
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