Vaccines work

Vaccines are a proven way to prevent serious infections. In this section you will learn more about the importance of vaccines, vaccine safety, vaccine development, and vaccine safety monitoring. You will also find answers to some common myths about vaccines. 

Vaccine confidence is an important focus for Ottawa Public Health. Vaccine misinformation is widespread and can be a deterrent to vaccine confidence. We are here to provide trustworthy, science-based information to help you understand why Ottawa Public Health promotes vaccines as an important, reliable and safe way of protecting you and your loved ones from vaccine preventable diseases.  

What is the difference between vaccines, vaccinations, and immunizations?
You may see the words vaccine, vaccination and immunization across our website. A vaccine is the actual product being given to a person to protect them from a disease. Most vaccines are given by injection (with a needle) but some can be given orally (by mouth) or nasally (sprayed in the nose). Vaccination is the process of giving a product (vaccine) to a person to provide protection from a particular disease and immunization is the process of being protected from a disease. However, people often use the terms “vaccination” and “immunization” interchangeably. All of this is to make sure you get immunity. Immunity means to have protection from a disease so that you can be exposed to a disease without becoming sick.
Why are vaccines important?
Vaccines protect people against very harmful and serious diseases like measles, polio, meningococcal, tetanus, diphtheria, and more. Vaccines are given to prevent you from getting a disease, before it has a chance to make you sick. This is different from most medicines that you take after you become sick.

Vaccines save lives: Vaccines have saved more lives in Canada than any other medical intervention in the past 50 years. The World Health Organization estimates that vaccines save 2 to 3 million lives worldwide every year. They also protect against diseases that may not be deadly but can cause pain and permanent disability.

These diseases do still exist:  Diseases like tetanus, whooping cough and influenza (the “flu”) are continually present in Canada. Other diseases are common in parts of the world with different immunization programs from Canada. Due to international travel these diseases can easily arrive in Canada. It is important for us to maintain high rates of immunization to keep them from infecting others and spreading.

If other people are immunized why do I need to be?
“Herd immunity” is when enough people are protected from a disease by vaccination that the disease cannot spread and those few who are not immunized are “protected” by the “herd” (unless they are directly exposed). Ideally, herd immunity is achieved when a sufficiently large percentage of the population has immunity against the disease. For some very transmissible diseases such as measles, as high as 95% of the population have to be vaccinated to achieve herd immunity. Diseases have the potential to cause outbreaks if herd immunity is not reached. This can happen when vaccination rates decrease. Some people are not able to receive vaccines because they are too young, like babies, or those who have a medical reason, like those who are being treated for cancer. These people rely on herd immunity to keep them safe.  
How are vaccines approved in Canada?

Health Canada’s independent drug authorization process is based on scientific and medical evidence for safety, efficacy, and quality. Candidate vaccines are required to have gone through pre-clincal trials, and then human clinical trials, with progressively more participants, to demonstrate safety and efficacy data, which is independently reviewed by Health Canada. Candidate vaccine producers are required to have a manufacturing facility with demonstrated quality controls for the vaccine.If there is not enough evidence to support safety, effectiveness or manufacturing quality of a vaccine, Health Canada does not authorize the vaccine and the product cannot be sold in Canada. The benefits of the vaccine must also outweigh any risks. 

For an in-depth look at the steps involved in regulating vaccines in Canada, click here.   Vaccine development and approval in Canada - 


To account for the urgent public health needs for COVID-19 vaccines, Health Canada provided mechanisms for an expedited authorization process. Health Canada’s independent evaluation of scientific and medical evidence for safety, efficacy and quality of COVID-19 vaccines is maintained, and Health Canada will make publicly available any safety and efficacy evidence used to issue expedited authorization. 

For more information about the expedited authorization process for COVID-19 drugs and vaccines, click here:  

How is vaccine safety monitored after being approved for use?  

Vaccines that are on the market for use in Canada are continuously being monitored for safety, so that adverse events following immunization as rare as 1 in 10,000 could be detected. Health Canada and the Public Health Agency of Canada (PHAC) share this responsibility, called post-market surveillance 

Adverse events following immunization are reported by vaccine recipients, health care providers who delivered the vaccine, public health units, hospitals, and vaccine manufacturers to Health Canada and the Public Health Agency of Canada (PHAC), as part of the Canadian Adverse Events Following Immunization Surveillance System (CAEFISS). Adverse events that could be caused by the vaccine, or vaccine manufacturing will be investigated, and changes to licensing, and recommended use would be communicated back to the public by Health Canada and the Public Health Agency of Canada. 

Adverse Events Following Immunization (AEFI)
An adverse event following immunization (AEFI) is an unwanted or unexpected health effect that happens after someone receives a vaccine, which may or may not be caused by the vaccine. Vaccine recipients are encouraged to report possible adverse events following immunization to the health care provider who delivered their vaccine.

Health care providers and immunization providers (i.e. physicians, nurses and pharmacists) are required by law to report AEFIs to their local public health authority.

You can access vaccine safety reports here:

Vaccine Safety

After approval, vaccines are continually monitored through a “vaccine safety surveillance” to ensure their safety.

For as long as a vaccine is used in Canada, its quality and safety is checked and rechecked and monitored by:

  • Health Canada Scientists
  • doctors, nurses and pharmacists who give the vaccine(s)
  • public health teams (Ottawa Public Health is involved in this surveillance process by investigating all reports of an Adverse Event Following Immunization (AEFI) and reporting them to Public Health Ontario)

Watch a video on vaccine safety  

Download a poster on vaccine safety

See also the sections on How is vaccine safety monitored after being approved for use and Adverse Events Following Immunization (AEFI).

What are the side effects of vaccines

Just like any medicine, vaccines can cause side effects. Most of these side effects are minor and last a few hours to a few days after vaccination. 

These side effects are the body’s natural response, as it is working hard to build immunity against the disease. This is known as the inflammatory response or reaction. These common side effects should not disrupt your daily life and your normal activities.  

Common vaccine side effects may include: 

  • mild fever, fatigue, muscle pain, joint pain, headache, nausea 

  • redness, soreness or swelling in the arm or leg where the vaccine was given 

Babies and young children can also be more fussy/temperamental than usual. 

If you or your child experience any unusual symptoms after your vaccination appointment, call your: 

  • health care provider or 

  • call Ottawa Public Health at 613-580-6744 (your health care provider will then report the information to their public health department. These reports are tracked and investigated) 

Serious reactions to vaccines are very rare. These may include: 

  • a fever above 40°C (104°F) 

  • crying or fussing for more than 24 hours 

  • worsening swelling where the needle went in  

  • unusual sleepiness 

  • hives 

  • swelling of the mouth or throat 

  • difficulty breathing, hoarseness or wheezing 

  • fast heartbeat, dizziness 

For any of these serious reactions, seek medical attention immediately. 


Myths about vaccines

Vaccines can cause autism spectrum disorder (ASD)  

There is a myth that vaccination can cause autism spectrum disorder (ASD)This myth originated from a 1998 case series published by UK physician, Andrew Wakefield. The study suggested that the measles, mumps, rubella (MMR) vaccine was responsible for autism in British children. 

This study was later found to be fraudulent. Scientific data has shown that there is no relation between vaccination and ASD 

Vaccines contain toxins
Vaccines contain antigens, which are small amounts or parts of the disease germ (either a virusbacteria, or toxoid). The germs can either be dead (inactive) or a weakened version of that germ (attenuated). Weakened live vaccines do not cause serious illness 

Vaccines also contain ingredients to prevent contamination (to keep the vaccine sterile and clean). These ingredients are present in very small amounts and do not pose a health risk. 

Vaccines may also contain adjuvants to boost the immune response to a vaccine. These ingredients are present in very small amounts and do not pose a health risk. 


The flu (influenza) vaccine causes the flu  
The flu vaccine contains inactivated (killed) virus and cannot give you the flu. The flu is spread through coughing, sneezing and talking while being in close contact with someone who has the flu. The flu vaccine can cause mild side effects such as redness at the injection site, mild flu-like symptoms such as low-grade fever, muscle aches and tiredness. This does not mean you have the flu; these side effects are normal and can last 1 to 2 days.  

Any serious or adverse side effect should be reported to your health care provider.  

Combining vaccines can cause adverse side effects 
Giving several vaccines to a child at the same time has no negative effect on a child’s immune system. It reduces discomfort for the child and saves time and money. Children’s immune systems can easily handle many vaccines at the same time. Researches have estimated that if an infant was given 11 vaccines at one time, that would only use about 0.1% of the immune systems capacity (Addressing Parents’ Concerns: Do Multiple Vaccines Overwhelm or Weaken the Infant’s Immune System? | American Academy of Pediatrics (   
There is so much information about vaccines. How do I know what is true? 
 With so much information at your fingertips, it can be challenging to know what to believe. Be it online or in print, make sure the information you are reading is up-to-date, and from a credible source. Talk about the information you have read with a trusted health care provider, like your family doctor or an Ottawa Public Health nurse. 

The websites listed at the bottom of this page are reputable sites that provide accurate and peer reviewed information. Refer to these sites when doing research about vaccination. 

Flu vaccine 

If you have received a flu vaccine, it will not protect you from becoming infected with COVID-19 but will help prevent the flu (influenza) if influenza were to circulate at the same time as COVID-19. Getting the flu can make you very sick and could make you more vulnerable to other infections. Getting the flu vaccine is also an important way to prevent cases of the flu and help protect our health system this upcoming fall and winter. 

Getting the flu vaccine will not increase your risk of illness from coronavirus, as demonstrated in this recently published Canadian research study. 


Contact information

Provincial Vaccine Information Line

  • Monday to Friday (holidays excluded) from 8:30 am to 5 pm, Eastern Time
  • Call if you have questions about Ontario's COVID-19 vaccination program.
  • Service is available in multiple languages.
  • Telephone: 1-888-999-6488
  • TTY: 1-866-797-0007

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