Flu Shot: What is it, How Does it Work, Risks and Benefits

Woman receiving a flue shot

Many of us are familiar with the sounds of constant sneezing and coughing, especially during the colder seasons. At some point in our lives, most of us would have taken a sick day or two from work because of ‘the flu’.

So, what exactly is ‘the flu’?

Flu, or Influenza is a widespread, infectious disease caused by the Influenza virus, which affects millions of individuals each year; it is more commonly known by its layman term: ‘the flu’. Although many of us recover with little problem, the severity of the disease can vary greatly. While most infected people generally recover in 7-10 days,1 the flu can cause severe complications and lead to hospitalization in people with compromised immune systems.

Despite the high number of flu cases in some years, there are various ways to protect yourself against the risk of contracting the flu. One common practice is to receive a seasonal flu vaccine, also known as a flu shot.

What is a Flu Shot?

A flu shot is a vaccine developed to protect against infection caused by the influenza virus. Although a flu shot does not prevent you completely from falling sick, it can reduce your risk of catching the infection.

This is because some types of the vaccine contain small traces of inactive influenza virus, which when introduced, triggers your immune system into developing antibodies suitable to fight against the disease.

These traces of inactive influenza virus cannot give you the flu, although it generally takes 2 weeks for the recipient to start developing antibodies. During this time, you may still fall sick if exposed to the virus.2 As such, it is advised to get your flu shot before the peak periods of the flu season so that the vaccine has time to take effect.

Who Should Get the Flu Shot?

The flu vaccine is recommended for all who are six months or older, 3 and is particularly essential for the following high-risk groups: 4 ,5

  • Individuals with health-related complications (i.e. asthma, diabetes, AIDS, obesity etc.)
  • Seniors who are 65 years or older
  • Young children
  • Pregnant women
  • Healthcare workers

As your antibodies fluctuate every year, it is important to ensure you have enough immunity to protect yourself against the common flu, even if you are young and feel healthy. 6

Remember to check with your doctor before receiving a flu vaccine if you had a previous allergic reaction to a flu shot.

How Effective is a Flu Shot?

Flu viruses can evolve and adapt rapidly. As such, last year’s flu shot may not protect you from the new strain of viruses that emerge a year later. 6 A new flu shot is released each year based on research on current circumstance, and to ensure the vaccine remains up to date in its effectiveness.

If a group of strains are predicted to be more prominent this flu season, a vaccine will be produced to tackle those strains 7 Among other factors such as an individual’s age or health, a vaccine’s effectiveness is greatly dependent on how well the flu shot matches with current circulating flu strains. 8 This is often challenging to predict as viruses can change within the period of vaccine production.

In order to ensure that you benefit from a flu shot, remember to get vaccinated early and practice good hygiene. Getting a vaccine does not mean you should be in close contact with someone who is severely sick with the flu or touch your face without washing your hands.

Benefits of a Flu Shot

It is essential to remember that even when there's a less-than-ideal match against all the circulating flu strains the seasonal flu vaccine can still offer benefits and protection against the viruses that do match. If you do end up with the flu, the flu vaccine may reduce the severity of any flu-related symptoms.

Some of the benefits of getting a flu shot include: 8

  • Less frequent trips needed to the doctor for flu-related illnesses
  • Where the vaccine matches the circulating viruses for the season, the flu shot has been shown prevent the flu in up to 60% of the population
  • Decreased flu-related hospitalization

A flu shot is a great preventative measure and can also help protect the people around you. If you live with young children, seniors, or have family members or friends who are more vulnerable to contracting the flu, a vaccine can help prevent you from catching and passing on the virus.

Types of Flu Shots Available

Flu vaccines are now available in the form of a nasal spray or injection. The type of vaccine you can get depends on your age, health, as well as your province's guidelines: 9

  • Flu Shot: this method of vaccination is administered with a needle, as an injection to the arm. The viruses in this method of vaccination are inactive.
  • Nasal Spray Flu Vaccine: this method of vaccination is administered as a nasal spray, and is approved for use in healthy, non-pregnant individuals, from ages 2 – 59 years of age. The viruses in this method of vaccination are called Live Attenuated Influenza Vaccine (LAIV), meaning the virus is active but weakened so it cannot cause flu illnesses. Similar to traditional vaccinations, the LAIV prompts your body in building up the necessary antibodies to fight the virus.

Unlike the standard method of Flu Shot administration via a needle, the Nasal Spray Flu Vaccine has a wider range of limitations. Some individuals who are unsuitable to receive the Nasal Spray Flu Vaccine include: 9

  • Children younger than 2 years old
  • Adults 59 years and older
  • People with a history of severe allergic reaction the vaccine
  • Individuals with weakened immune systems
  • Pregnant women

In order to determine which method of vaccination is suitable for you, consult with a healthcare provider.

What Side Effects Could Occur?

The side effects in individuals vary and are typically mild and resolve on their own after a few days. The most common side effects from a flu shot include: 10

  • Soreness, redness, tenderness or swelling where the shot was administered
  • Low-grade fever
  • Headache
  • Muscle ache
  • Sore throat, cough, or runny nose

If an individual experiences any side effects, it usually begins soon after vaccination. It is important to stay at the clinic for 15 minutes after your vaccine to monitor for any reaction. In most cases, the common side effects experienced after a flu vaccine are considerably less severe than the symptoms caused by the actual flu illness.

It is recommended to let your doctor, nurse, or pharmacist know if you have a history of allergy, or any severe reaction to any part of the flu vaccine.

Where Can I Get a Flu Shot in Canada?

The flu shot is widely available in many places, including doctor’s offices, participating pharmacies such as Rexall.ca or Shoppers.ca, Ontario Flu Shot Clinics, and Walk-in Clinics.11

Although the flu shot is not 100% effective, it is a key preventor in reducing risks associated with flu-related illnesses. If you are unable to take the flu vaccine due to health reasons, or you have missed a flu vaccination, practice good hygiene to protect yourself. This includes:

  • Washing your hands with soap and water frequently
  • Sanitizing high traffic areas
  • Avoiding contact with people whom you know are unwell
  • Taking care of your body to ensure good immunity
  • Avoiding touching your face with unwashed hands

Falling sick cannot always be avoided, but you can trust TYLENOL® to provide fast and effective symptom relief due to common cold and flu. If you are looking to get through the day or rest at night, check out TYLENOL® Complete Cold, Cough & Flu.


  1. https://www.webmd.com/cold-and-flu/qa/how-long-do-colds-usually-last-and-do-they-require-medical-care
  2. https://www.cdc.gov/flu/prevent/keyfacts.htm
  3. https://www.canada.ca/en/public-health/services/diseases/flu-influenza/get-your-flu-shot.html#a2
  4. https://www.canada.ca/en/public-health/services/diseases/flu-influenza/get-your-flu-shot.html#a2
  5. https://www.healthlinkbc.ca/health-topics/abr9348
  6. https://www.mayoclinic.org/diseases-conditions/flu/in-depth/flu-shots/art-20048000
  7. https://www.cdc.gov/flu/prevent/keyfacts.htm
  8. https://www.ontario.ca/page/flu-vaccine-safety-effectiveness#section-3
  9. https://www.canada.ca/en/public-health/services/publications/vaccines-immunization/canadian-immunization-guide-statement-seasonal-influenza-vaccine-2019-2020.html#II6
  10. https://www.albertahealthservices.ca/assets/healthinfo/hi-flu-influenza-vaccine-information-sheet.pdf
  11. https://www.canada.ca/en/public-health/services/diseases/flu-influenza/flu-clinics-across-canada.html


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