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Information about the Flu

What is influenza?

Influenza is an acute respiratory illness that is caused by a virus. People who get influenza may have a fever, chills, cough, runny nose, sore throat, headache, muscle aches, extreme weakness and fatigue. Children can also have earaches, nausea, vomiting and diarrhea.

Influenza spreads through respiratory droplets from infected persons, for example, through coughing or sneezing. It is also spread through direct contact with surfaces and objects contaminated by the influenza virus, such as toys, unwashed eating utensils and unclean hands.

How are individuals protected against influenza?

Influenza vaccine is the best defence against influenza. The National Advisory Committee on Immunization (NACI), a national expert group on immunization, strongly recommends annual influenza immunization.

Vaccine choices

NACI recommends that children aged 6 months to 17 years of age receive a quadrivalent vaccine. Until recently, seasonal influenza vaccines were designed to protect against three different influenza viruses, and so were referred to as trivalent influenza vaccines (TIV). The seasonal trivalent influenza vaccine protects against two influenza A viruses and one influenza B virus. However, there are two different types of influenza B viruses that can circulate in a given influenza season and the recently introduced quadrivalent vaccine provides protection against both types of influenza B. The quadrivalent vaccine therefore offers broader protection against the influenza B viruses that may circulate.

Vaccine choices for children include the nasal mist or injection and will vary upon their age. Both vaccines protect against the four flu viruses most likely to circulate during flu season.

The flu vaccine for adults will remain available in an injectable form, with protection against the three flu viruses most likely to circulate during the flu season. Influenza B affects children and adolescents more frequently that it affects adults, therefore the quadrivalent influenza vaccine is not yet available as a publicly funded vaccine for adults.

How well does the vaccine protect against influenza?

Influenza immunization builds up antibodies against the influenza viruses in the vaccine, making it easier to fight influenza infection before it starts. The quadrivalent influenza vaccine offers broader protection than the trivalent influenza vaccine since it contains four strains of influenza virus, two influenza A strains and two influenza B strains. The TIVs and quadrivalent influenza vaccine provide the same degree of protection against the three strains they share in common. Generally influenza vaccines offer about 60% protection when the vaccine and circulating strains are well matched. The quadrivalent influenza vaccine will offer extra protection if the additional B strain in that vaccine is in circulation during influenza season.

It takes about two weeks following immunization to develop protection against influenza; protection can last up to one year. People who receive the vaccine can still get influenza but if they do, they may not get as sick. The vaccine will not protect against colds and other respiratory illnesses that may be mistaken for influenza, but are not caused by the influenza virus.

Do I need to get the influenza vaccine every year?

Yes, the influenza vaccine is needed each year. The influenza virus changes often, so it is necessary to get immunized with influenza vaccine every year for protection from the new virus strains that may be circulating that year.

Is the influenza vaccine safe?

The influenza vaccine is safe and well tolerated. Influenza vaccines that protect against four influenza viruses are made in the same way as the influenza vaccines that have been around for years that protect against three influenza viruses. These vaccines have undergone the same testing as other vaccines approved for use in Canada.

What are the side  effects of the flu vaccine?


Mild pain, swelling, and / or redness in arm where the needle was given.

Some may experience mild fever and / or muscle aches within 6-12 hours after getting vaccinated. These side effects may last 1-2 days.

Less Common

Call your health care provider or local health unit if within 24 hours of receiving your vaccination you have any of the following symptoms:

  • Red eyes
  • Cough
  • Wheezing
  • Difficulty breathing
  • Hoarseness
  • Sore throat
  • Facial swelling


Call your health care provider or go to the nearest emergency room if you have any of the following symptoms:

  • High fever (38°C or 100.4°F)
  • Lasting or worsening weakness
  • Hives
  • Dizziness
  • Swelling of the lips, tongue or face
  • Convulsions
  • Trouble breathing
  • Another serious condition that you think might be a reaction to the vaccine

What do I do if I think myself or my child has the flu?

Stay home if you are sick and keep your child home from school or daycare if they are sick. Seek medical attention but call ahead to your health care provider's office or the emergency department to ensure they have proper precautions in place to protect others.

To prevent spreading the influenza virus, cough and sneeze into your sleeve, keep commonly touched surfaces cleaned, and clean your hands frequently and thoroughly.