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Everything You Need to Know About the Flu Shot

Updated October 22, 2021

It’s Flu Season!

This year’s flu season is busier than ever with a surge in vaccinations compared to previous years due to the “twindemic” with COVID-19. Pharmacies are hustling to provide over 100 flu shots daily on top of their regular day-to-day tasks, and patients are patient-ly waiting for more doses to become available as supply runs low. Due to the current pandemic, it’s important now more than ever to be educated on how the flu virus works and how we can protect ourselves against it.

What is influenza (aka “the flu”)?

Influenza is a contagious respiratory illness killing approximately 500,000 people every year. The flu is caused by two main types of the influenza virus (types A and B). Flu season typically runs from October to February of the next year, and the virus can be spread through respiratory droplets up to 6 feet away or by touching contaminated surfaces. Symptoms may include fever, chills, cough, sore throat, fatigue, muscle aches, and/or headaches. Infected individuals are contagious for up to 7 days after contracting the virus. However, they may not develop symptoms until 2 days after becoming infected, allowing the possibility for them to infect others before even knowing that they are sick.

How does the flu shot work?

The influenza vaccine contains 3 (trivalent) or 4 (quadrivalent) weakened or inactivated influenza type A and type B strains. When injected into a person’s body, their immune system recognizes these antigens as ‘foreign’ and triggers the body to produce antibodies that will fight against the virus. It takes 2 weeks for these antibodies to develop and protect the person from future infection. If exposed to the same virus again, the body’s immune system will already have the antibodies to fight it off. This is called “adaptive immunity.”

The target strain for the flu vaccine is recommended by the World Health Organization each year, 6 months before the start of flu season to allow enough time for the vaccine to be produced. Although the effectiveness of the flu shot may vary based on how well the vaccine matches the active influenza strain, studies have demonstrated a 40-60% risk reduction in the overall population.

Why do we need the flu shot every year?

As the flu virus replicates, it can either undergo small genetic mutations (‘antigenic drift’) or major protein changes (‘antigenic shift’). These processes ultimately change the surface proteins (or ‘antigens’) of the virus. When this happens, our body’s immune system may not recognize this new strain and will not be able to fight it off, making us susceptible to infection from the flu. Getting vaccinated each year is the #1 way to protect yourself and those around you from the disease and any associated complications.

Who should get the flu shot?

Everyone 6 months of age and older should receive the flu vaccine every year in October. Children under the age of 9 who are getting vaccinated for the very first time also require a second dose administered one month after the first. It is especially important for individuals at high risk of developing complications from the flu, such as pneumonia, dehydration, worsening of chronic conditions, or even death, to get vaccinated. This includes:

  • Children under the age of 2

  • Pregnant women

  • Seniors over the age of 65

  • Immunocompromised individuals

  • Patients with chronic health condition

But I'm afraid of needles!

To put things into perspective, we typically use a 25-gauge (or ~0.5 mm) needle which is as thin as 10 strands of hair. However, if you have needle phobia, there is another option! FluMist is a nasal spray flu vaccine approved for individuals 2 to 49 years old. Some side effects may include a runny or stuffy nose, sore throat, low-grade fever, headache, muscle aches, or vomiting. There are some individuals who should NOT receive this vaccine, such as children ages 2-4 with asthma, pregnant women, those with chronic conditions, and patients with cochlear implants. Ask your health care professional if this is right for you!

*One thing to note is that the nasal spray flu vaccine is NOT covered by the government in Ontario, Nova Scotia, and New Brunswick, so you will have to pay out of pocket to get it.

Is there a chance I can get sick from the flu shot?

The flu vaccine cannot directly cause the flu itself. This is because the vaccines are made with either weakened or inactivated viruses that are non-infectious. However, there are some flu-like side effects that patients may experience after immunization as their body initiates the immune response, such as fever, cough, headache, fatigue, and/or sore throat. These symptoms are typically mild and transient. In addition, there is a very small risk of developing Guillain-Barré Syndrome (GBS) from the injectable flu vaccine in which the body's immune system attacks its own nerve cells, but this risk is fewer than 1-2 cases per million. Further, some patients may develop an allergic reaction to the vaccine if they have allergies to egg protein or any other component of the vaccine. This is why you are asked to wait around for 15 minutes before you leave, just to make sure that you are okay.

Due to the fact that the target strain for the flu vaccine is determined 6 months before flu season, there is a chance that the vaccine may not completely match the circulating influenza virus. In this case, the vaccine may not provide full protection against the virus. However, studies have shown that even in people who do end up getting sick, vaccination reduces the severity and complications of the illness.

What’s the difference between the regular and high dose flu shot?

Due to the naturally-weakening immune system (a phenomenon called “immunosenescence”), the regular-dose flu shot is not as effective in the elderly compared to healthy adults. That is why a high-dose vaccine exists for people 65 years and older. It contains four times the amount of antigens than the regular dose, thus promoting a stronger immune response to the flu virus. Studies have shown that the high-dose vaccine was 24% more effective in preventing the flu and was associated with a lower risk of hospital admissions compared to the regular dose in ages 65 and older.

These days, it can be difficult to find a clinic that has the high-dose flu shot available due to demand exceeding supply. The Advisory Committee on Immunization Practices has not stated any preference for one flu vaccine over another for people 65 years and older, so if the regular dose is the only option available to you, just remember that some protection is better than none at all!

Where can I get my flu shot?

Flu vaccines can be administered at the following locations:

  • Doctor’s office (with a valid OHIP card)

  • Pharmacies (over the age of 2 with a valid OHIP card)

Keep in mind that most locations now require appointments to get the flu shot, so make sure you check the policy before you go. Please be patient when waiting for your flu shot and remember to say thank you to your health care worker! We are all doing our best to provide for our patients under the current circumstances to make sure everyone stays healthy.

How can I stay updated on the flu virus?

FluWatch is Canada’s national flu surveillance program that monitors and reports the influenza activity levels across Canada every week. If you would like to help public health officials track the flu, you can sign up to be a FluWatcher in which you will answer 2 quick health-related questions each week.

So.....who's ready to get their flu shot?!

Click here to view our infographic!

Still not convinced on getting the flu shot? Have more questions? Let us know in the comments below!



  1. Flu (influenza): For health professionals. Government of Canada. Updated October 23, 2020. Accessed October 28, 2020.

  2. Influenza (Flu). Centers for Disease Control and Prevention. Updated October 27, 2020. Accessed October 28, 2020.

  3. Aw D, Silva AB, Palmer DB. Immunosenescence: emerging challenges for an ageing population. Immunology. 2007; 120(4): 435-446. doi: 10.1111/j.1365-2567.2007.02555.x.

  4. Flu (influenza): FluWatch surveillance. Government of Canada. Updated October 19, 2020. Accessed October 28, 2020

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