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Influenza (the Flu)

Influenza (commonly known as “the flu”) is a respiratory infection caused by the influenza A and B viruses. Do not confuse it with "stomach flu" and other illnesses. People of all ages, including the young and healthy, can be affected by the flu. Learn about the flu, symptoms, prevention and the flu vaccine.

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Stopping the spread

How flu spreads

The flu is spread from infected persons through:

  • Coughing
  • Sneezing
  • Touching surfaces that have been contaminated by an ill person (such as toys, doorknobs, utensils or unwashed hands) and then touching your eyes, nose or mouth

Protecting yourself and others from the flu

Follow these steps to protect yourself and others from influenza:

  • Get the flu vaccine to protect yourself and others.
  • Keep an alcohol-based hand sanitizer handy at work, home and in your car.
  • Stay home and avoid contact with others if you do not feel well. If you can, sleep in a separate room from others until you are well.
  • Do not visit long-term care and retirement homes, as well as hospitals if you have been ill or have had contact with someone who is ill. Please help protect vulnerable persons and other individuals at high risk.
  • Cough into your sleeve or a tissue and not your hands. Dispose of the tissue immediately, and wash your hands thoroughly.
  • Clean and disinfect all contaminated surfaces and frequently touched surfaces, such as doorknobs, faucet taps, light switches and toilet handles.
  • Wash your hands frequently with soap and water. Use an alcohol-based hand sanitizer when soap and water are not available.
  • Continuing to follow COVID-19 public health measures including wearing a mask, practicing hand hygiene and physical distancing will help to keep cases of flu low this year.


Flu symptoms


Typical flu symptoms include the sudden onset of:

  • Fever
  • Headache
  • Muscle aches and pains
  • Fatigue
  • Cough
  • Loss of appetite
  • Runny nose
  • Watery eyes
  • Throat irritation

Children can also get:

  • Earaches and ear infections
  • Nausea
  • Vomiting
  • Diarrhea
  • Croup

Most people recover within a week to ten days, but the cough and fatigue can take much longer to resolve.

Most us of are at risk of infection from the influenza virus. People at greater risk of complications from flu include:

  • Adults and children with certain chronic medical conditions including:
    • Anemia
    • Asthma
    • Lung, heart and kidney disease
    • Neurologic or neurodevelopment conditions
    • Diabetes
    • Cancer
    • Weakened immune systems due to disease or medication
    • Morbid obesity
  • Residents of nursing homes and chronic care homes
  • Persons 65 years of age and older
  • Children under 5 years old
  • Pregnant women
  • Indigenous peoples

Colds, vomiting, diarrhea (often referred to as "stomach flu") and other viral infections are often confused with the flu but different viruses cause them.

Cold and Flu symptoms are similar to the symptoms of COVID-19. For more information about signs and symptoms of COVID-19 and whether you need to get tested, visit the COVID-19 (2019 Novel Coronavirus) webpage.

Symptoms Cold Influenza
Fever Rare Usual, high fever (39°C/102°F - 40°C/104°F); sudden onset, lasts 3-4 days
Note: The elderly and people who have a weakened immune system might not develop a fever.
Headache Rare Usual, can be sudden
Muscle aches & pains Sometimes, generally mild Usual, often severe
Tiredness & weakness Sometimes, generally mild Usual, severe, might last 2-3 weeks or more
Extreme fatigue Unusual Usual, early onset, can be severe
Runny, stuffy nose Common Common
Sneezing Common Sometimes
Sore throat Common Common
Cough/chest discomfort Sometimes, mild to moderate Common, can become moderate to severe; cough might last for weeks
Complications Can lead to sinus congestion or infection, and ear aches* Can lead to pneumonia, can worsen a current chronic condition, can be life threatening

* Colds do not generally result in serious health problems, such as pneumonia or bacterial infections.

Note: Children might also experience the croup, ear infections, nausea, vomiting and diarrhea when they have influenza – symptoms that are not common in adults.

Please note, these symptoms are subject to change. For the latest on symptoms, visit the Ontario Ministry of Health’s Guidance for the Health Sector webpage (external link).

Treatment and recovery

How to recover from the flu

There are several steps you can take to help yourself and to help reduce the spread of illness to others:

  • Drink a lot of fluid.
  • Get plenty of rest.
  • Take a pain reliever (aspirin or acetaminophen) for head and muscle aches. Children and teenagers who have the flu should avoid aspirin unless specifically directed by a physician.
  • Contact your family doctor if illness persists or becomes worse, or call Telehealth at 1-866-797-0000, TTY 1-866-797-0007 to speak with a registered nurse.
  • While you are sick, make sure to reduce spread to others by taking the protective steps above.


Please read the list of frequently asked questions below about the flu, who should get it, where to go to get the shot and other information.

The flu vaccine is made each year to protect against strains of the influenza virus that are expected to be circulating in the community in the upcoming influenza season. The vaccine stimulates your body’s immune system to build antibodies against influenza, making it stronger and ready to fight off the illness before it starts.

The National Advisory Committee on Immunization (NACI) (external link), which advises the Public Health Agency of Canada, recommends the flu vaccine for everyone 6 months of age and older. It is especially recommended for persons:

  • at high risk for complications of flu;
  • who might spread influenza to high-risk people; and
  • who provide essential community services.

Individuals who should not get the flu vaccine include anyone who:

  • has had severe allergic reaction to a past influenza vaccine such as:
    • hives
    • throat and/or tongue swelling
    • difficulty breathing or shock
  • has a severe allergy to any part of the vaccine except egg;
  • has a new or worsening illness, with or without fever (however, if you have a cold or other minor illness, you can still be immunized);
  • has had Guillain-Barré Syndrome within 6 weeks of a past influenza vaccine;
  • has had Oculorespiratory syndrome with lower respiratory symptoms;
  • is under 6 months of age.

If you fall into any of the above categories, depending on the situation, you might need to speak with your physician, or return after an appropriate time interval.

A flu vaccine is available for:

  • People six months and older, which provides protection against four common strains of flu virus.
  • Older adults, age 65 and older, are eligible to receive either the regular quadrivalent (4-strain), adjuvanted trivalent (3 strain), or the high-dose quadrivalent (4-strain) flu vaccine. High-dose vaccines are recommended for seniors at high risk due to age or in the community with multiple co-morbidities.
    High-dose vaccines are not available and are not recommended for populations under 65 years of age.

Talk to your doctor about any questions you have about the flu vaccine.

To get your free flu immunization, book an appointment with:

  • your doctor
  • a local pharmacy*
  • a walk-in clinic

*Children under 2 years of age must visit their doctor. Looking for a family doctor? We can help.

Participating pharmacies are offering both the high-dose and regular flu vaccines. Find the closest participating pharmacy in:

Residents can also sign up to be notified when and where flu shots become available by visiting

Keep a record of your flu vaccination

  • After you get your immunization, you will be given a written record. Add this information to your immunization record.
  • If you received the vaccine at a pharmacy, share this information with your regular health care provider. 
  • If you develop respiratory symptoms over the next few months, this information will be an important part of your care plan.

Safety and side effects

  • The flu vaccine is safe. Most people who get the vaccine have either no or mild side effects. Mild side effects, which occur within one to two days after vaccination, include soreness, redness or swelling at the injection site.
  • Life-threatening allergic reactions are very rare. In very rare cases, the flu vaccine has been associated with Guillain-Barré Syndrome (GBS), a very uncommon disease that causes muscle paralysis. The risk is about 1 in one million doses of vaccine given.

Ocular respiratory syndrome (ORS)

  • In 2000-2001, a small number of people who received the influenza vaccine developed ORS.
  • ORS can cause red eyes, cough, chest tightness, difficulty breathing, hoarseness, sore throat and swelling of the face.
  • Symptoms occur within 24 hours and resolve within 48 hours.
  • Persons who experienced ORS in the past may safely have the flu vaccine but should talk to their health care provider before being immunized.

When do I seek medical attention?

As with other vaccines, you should stay on site in the health care provider’s office (or pharmacy) for at least 15 minutes after receiving your immunization. You should seek medical attention if you experience the following:

  • Swelling of the lips, tongue or face
  • Trouble breathing
  • Hives
  • Convulsions
  • Dizziness
  • Lasting or worsening weakness
  • High fever (40°C or 104°F)
Contact your family doctor or go to the nearest emergency room right away if you have any of these symptoms within 3 days of getting the influenza vaccine.

Influenza vaccine effectiveness can vary from year to year and among different age and risk groups. It cannot protect you from other types of viruses circulating in the fall/winter months that can cause illness much like influenza. The body needs two weeks to build up protection to the flu virus after you receive immunization; protection might last up to one year.

High-dose quadrivalent vaccine (QIV-HD), adjuvanted trivalent vaccine (TIV-adj) and standard dose quadrivalent vaccines (QIV) are available for adults 65 years of age and older.

It is recommended that adults 65 years of age and older receive high-dose QIV, as it provides higher protection against Influenza A (H3N2), which is the predominant strain seen in this age group. However, Halton Region Public Health recommends getting vaccinated as soon as possible. Do not delay vaccination to wait for a particular product. QIV, TIV-adj, and QIV-HD protect against the flu and it is most important for older adults to be vaccinated.

Flu vaccine decision making should be discussed with your health care provider.

FluMist® (intranasal spray) is not available this year through the publicly funded flu program but is available for purchase. Please contact your pharmacy/physician for more information.

  • The Ministry of Health orders the vaccine for the province of Ontario.
  • The vaccine arrives at the Ministry’s central pharmacy in multiple shipments over a period of two to three months. Typically, the first shipments of flu vaccine arrive by the beginning of October.
  • As the shipments come in, each Public Health Unit and pharmacy distributor receives a portion of those shipments.
  • Public Health Units then send vaccine out to local health care providers. Pharmacy distributors send the flu vaccine out to the pharmacies.

When can I receive my flu vaccine?

Month heading
End of September to early October
  • Hospitalized individuals and hospital staff
  • Long-term care home residents and staff
  • Individuals at high-risk for flu related complications or hospitalization
    • All pregnant women
    • People who are residents of nursing homes or other chronic care facilities
    • People 65 years of age and older
    • All children 6 months to 4 years of age
    • Indigenous Peoples
    • Adults or children 6 months of age and over with chronic health conditions as follows:
      • Cardiac or pulmonary disorders
      • Diabetes mellitus or other metabolic disease
      • Cancer
      • Conditions or medication which compromise the immune system (due to underlying disease, therapy or both)
      • Renal disease
      • Anemia or hemoglobinopathy
      • Neurologic or neurodevelopment conditions
      • Morbid obesity (body mass index of ≥ 40)
      • Children and adolescents (6 months to 18 years) undergoing treatment with acetylsalicylic acid for long periods
  • Health care providers
  • General population