What is it

Influenza, also known as the flu, is a contagious respiratory illness caused by influenza viruses. It can cause mild to severe infection of the nose, throat and lungs.1 Serious complications of flu infection can result in hospitalization or death.2 Some people, such as older adults, young children, and people with certain health conditions, are at higher risk for serious flu complications.2,3

Who is at risk

Anyone may get the flu if they are exposed to the virus.3 In Canada, your risk of getting the flu is higher in the late fall and winter months.3 The flu usually occurs between November and April.3 The risk is lower during the rest of the year.

The following activities may increase your chance of getting the flu:3

  • Crowded conditions, attending large group events or gatherings
  • Traveling on cruise ships or joining large commercial tours

Some people are more likely to get flu-related complications or be hospitalized due to complications. These include:3

  • People with underlying health conditions, such as
    • Cancer
    • Diabetes
    • Heart disease
    • Lung disease
    • Obesity
  • People 65 years and older
  • People living in nursing homes or long term care facilities
  • Children under 5 years of age
  • Pregnant women
  • Indigenous people

Some people are more likely to spread the flu to those at high risk of complications. They include:3

  • Family, household members, or caregivers who are in close contact with the listed higher risk groups
  • Those who care for or are expecting a newborn baby during flu season
  • Health care workers
  • Child care workers
  • Those who provide services to the higher risk group in closed settings

What are the symptoms

Symptoms appear 1 to 4 days after exposure to the influenza virus and typically lasts for 7 to 10 days.4 While most people make a full recovery from the flu, others may develop serious complications including pneumonia (a lung infection) and may require hospital care.4
Flu symptoms usually include the sudden appearance of:4

  • High fever (39oC and above)
  • Cough
  • Muscle aches

Other common symptoms include:4

  • Headache
  • Chills
  • Loss of appetite
  • Fatigue (tiredness)
  • Sore throat
  • Runny or stuffy nose

Some people, especially children, may also experience:4

  1. Stomach ache
  2. Diarrhea
  3. Nausea and vomiting

In comparison to the flu, symptoms of the common cold are usually milder with a more gradual onset of 2 to 3 days after exposure to the virus. Symptoms include:4

  • Runny nose
  • Sneezing
  • Cough
  • Sore throat

How is it spread

The flu is mainly caused by 2 types of viruses, influenza A and influenza B.1

The influenza virus can be easily spread from person to person, even before symptoms start to appear.1 Most healthy adults may be able to infect other people beginning 1 day before symptoms develop and up to 5 to 7 days after becoming sick.5 An infected individual can spread it to others by:1

  • Sneezing
  • Coughing
  • Talking

These actions all result in the release of tiny droplets containing the flu virus into the air.1

People can become infected if these droplets land on your:1

  • Nose
  • Mouth
  • Eyes

Infection can also occur if an individual touch any of these body parts after touching objects contaminated by infected droplets. Commonly contaminated objects include:1

  • Doorknobs
  • Phones
  • Television remotes
  • Hands of another person

How is it prevented

Getting a flu vaccine, also known as a flu shot, is the best way to prevent the flu.6,7 You cannot get the flu from the flu vaccine. Most people do not have reactions to the flu vaccine; severe reactions are very rare.6,7

The flu vaccine is effective because it:6

  • Protects you if you are exposed to the virus
  • Prevents you from getting very sick
  • Helps to protect other people because you are less likely to spread the virus to others
  • Confers immunity at a community level resulting in less cases of flu

Vaccination is recommended for everyone 6 months and older, especially for people who are at high risk of complications and those who are especially capable of spreading the flu to those at higher risk.6, 7

How is it treated

Mild flu symptoms can be treated with:8

  • Rest
  • Drink plenty of fluids
  • Medication to reduce any fever or aches

Over-the-counter cough and flu medicine should not be given to children younger than 6 years old. It is only safe to do so if advised by your healthcare provider.10

Antiviral medication may be prescribed by your healthcare provider if you are at high risk for flu-related complications, or you are ill enough to require hospital care. In these instances, antiviral medications should be started as soon as possible.8 Medical advice is recommended for the onset of symptoms. For further information regarding Flu and immunization, please speak with your healthcare provider.


  1. Government of Canada. Causes of Flu (influenza)
  2. Centers for Disease Control and Prevention. Seasonal Influenza (Flu) Basics.
  3. Government of Canada. Risks of Flu (influenza).
  4. Government of Canada. Symptoms of Flu (influenza).
  5. Centers for Disease Control and Prevention. How Flu Spreads.
  6. Government of Canada. Prevention of Flu (influenza).
  7. Ministry of Health Israel. Vaccination of Infants. Flu.
  8. Government of Canada. Treatment of Flu (influenza): Symptoms and treatment. .