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Influenza (the Flu)

What is influenza?

  • Influenza, or the flu, is an infectious respiratory disease that begins in the nose and throat (see symptoms below).
  • Influenza is caused by a highly contagious virus.
  • Influenza spreads rapidly from person to person - usually by coughing or sneezing.
  • Influenza viruses change over time to escape the immunity people develop from having influenza or the influenza vaccine in the past.
  • New vaccines are created to combat the new strains of the virus.
  • Influenza is rarely a serious disease, but its complications can be severe.
  • Influenza can incapacitate a person for five to 10 days and could lead to pneumonia or bronchitis.
  • Occasionally influenza can lead to death from influenza-related pneumonia, or from other influenza related complications such as an aggravation of underlying chronic heart and lung disease.

Influenza symptoms may include:

  • sudden high fever
  • headache
  • loss of appetite
  • severe muscle aches and pain
  • extreme fatigue and weakness
  • chills
  • dry cough
  • sweating
  • sore throat
  • runny nose
  • nasal congestion
  • sneezing
  • Occasionally nausea, vomiting and diarrhea may occur in children, but rarely in adults.
  • Influenza is not the 'stomach flu', which mainly causes abdominal upset and diarrhea with few other symptoms.

Is it a cold or influenza?

Both the cold and influenza viruses are spread from contact with someone who already has the illness or from surfaces contaminated with these viruses.

usual high fever
(102°F/39°C to 104°F/40°C) -
sudden onset, lasts 3-4 days
usual - can be severe
sometimes, mild
general aches and pains
usual - often severe
sometimes, mild
fatigue and weakness
usual, severe, may last
2-3 weeks or more
extreme fatigue
usual early onset -
can be severe
runny, stuffy nose
sore throat
sometimes, mild to moderate
chest discomfort,
usual - can be severe
can lead to sinus
congestion or
can lead to pneumonia
and respiratory failure;
can worsen a current
chronic condition;
can be life-threatening


How can I protect myself and others from influenza?

  • Wash your hands frequently with soap and warm water. Hand sanitizer can also be used when soap and water are not readily available.
  • Cough or sneeze into your sleeve or cover your nose and mouth with a tissue to protect others from your germs.
  • Teach your children to use good coughing etiquette and the importance of washing their hands.
  • If you are ill, stay at home (for example, stay home from work or school and public gatherings).
  • Get a flu vaccine (shot) every year.

Who should get the vaccine?

While everyone over 6 months of age is encouraged to receive the influenza vaccine, the following persons are at highest risk of serious illness from the influenza virus:
  • Those with chronic heart or lung conditions
  • Those with diabetes, cancer, kidney disease or illnesses which lower immunity to influenza
  • Pregnant women
  • Children aged 6 months to 4 years inclusive
  • Adults 65 years of age and over

People who have had a severe anaphylactic (life threatening) allergic reaction to eggs or to a previous dose of the vaccine should not receive the flu shot. Anaphylactic reactions occur within 20 to 30 minutes after the vaccine has been administered.

What will the vaccine do?

  • After vaccination, the body's immune system produces antibodies which then prevent infection, or reduce the likelihood of severe illness should infection occur.

Will the flu shot give me the flu?

  • You cannot get the flu from the vaccine. There may be mild symptoms of influenza, but the viral component of the vaccine is dead so it cannot multiply.
  • Generally it takes 2 weeks after receiving the flu vaccine for the body to develop immunity to the influenza virus .
  • People who become ill after receiving their shot may have caught a cold or another virus. It is also possible to catch another strain of influenza not included in the vaccine.

What should I do if I get the flu or develop flu-like symptoms?

  • Get plenty of rest
  • Drink a lot of liquids
  • Avoid using alcohol and tobacco
  • Stay home and avoid contact with other people to protect them from catching your illness
  • Some over-the-counter medications can help relieve the symptoms of flu such as fever, aches and pains.

ASA (aspirin) should not be given to children or teenagers unless specifically directed to do so by a doctor. The use of aspirin has been strongly linked with the development of Reye's syndrome, a rare disease that affects mainly children or teenagers during a viral illness such as chicken pox or influenza. Reye's syndrome can be fatal.

Antibiotics do not have any effect against a viral illness like the flu.

When should I see a doctor?

Most people recover from the flu within one week to 10 days. If symptoms last more than 10 days, or worsen, visit your family doctor or a walk-in clinic. See a doctor if any of the following symptoms are present:

  • High or prolonged fever
  • Fast breathing or trouble breathing
  • Bluish skin colour
  • Not drinking enough fluids
  • Changes in mental status such as difficulty waking, irritability, or seizures
  • Flu-like symptoms that improve but then return with fever and a worse cough
  • Worsening of underlying chronic medical conditions such as heart disease, lung disease or diabetes

Where can I learn more about influenza?

For more information, visit Health Canada's Flu website.

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