Vaccines & Safety

• Two doses of most COVID-19 vaccines are required for stronger protection from COVID-19.
• Early studies show that mixing COVID-19 vaccines produces a strong immune response.
• Mixing of mRNA vaccines (Pfizer and Moderna), as well as mixing AstraZeneca and an mRNA vaccine is safe, effective and allows more people to receive their second dose sooner.
  • Mixing similar vaccines to complete a vaccine series is routinely done for influenza, Hepatitis A, Hepatitis B, measles, and mumps vaccination.
  • Pfizer and Moderna vaccines use a similar mRNA technology, so the vaccines are interchangeable and safe to mix.
• It is common with any vaccine to have mild, short-term side effects such as a sore arm, tiredness, headache, fever or sore muscles.
  • There is a chance of increased mild, short-term side effects after receiving an mRNA vaccine as a second dose if you received AstraZeneca as your first dose. These side effects can include pain at the injection site, chills, headache, muscle and joint pain, and tiredness.
• If you have had a complete vaccine series, you are not eligible to receive additional doses for travel purposes.

If you received either Pfizer or Moderna vaccine for your first dose

• You may receive either Pfizer or Moderna vaccines as your second dose at a Halton Region vaccination clinic.
• Pfizer and Moderna vaccines use a similar mRNA technology so the vaccines are interchangeable.
• Pfizer vaccine is approved for those 12 years of age and older. Moderna vaccine is approved for those 18 years of age and older.
• It is not recommended to receive AstraZeneca as your second dose.

If you received AstraZeneca vaccine for your first dose

• You may receive either AstraZeneca or an mRNA vaccine (Pfizer or Moderna) as your second dose.
  • To receive the AstraZeneca vaccine, contact the pharmacy or primary care provider where you got your first dose to book an appointment.
  • To receive an mRNA vaccine, residents can book a single second dose appointment at a Halton Region vaccination clinic. Appointments will be booked at a minimum of eight weeks after your first dose and availability is contingent on vaccine supply. Residents can also book an mRNA vaccine directly with a participating pharmacy.
• There is a possibility of increased temporary short-term side effects after receiving an mRNA vaccine as a second dose, including pain at the injection site, chills, headache, muscle and joint pain and fatigue.

You can check the provincial portal to determine which vaccine type you received (external link) if you have a green health card or call the Provincial Vaccine Contact Centre at 1-833-943-3900 if you have a red and white health card.

• Getting a second dose of any COVID-19 vaccine as soon as you are eligible provides the best protection against COVID-19 and the variants of concern.
• The best vaccine for your second dose is the first one available to you.
• Being fully vaccinated for COVID-19 is not only your best protection against the virus, it also helps our community to return to the activities that people enjoyed prior to the pandemic.

The Pfizer-BioNTech COVID-19 vaccine uses a method called messenger RNA (mRNA) technology. The mRNA in the vaccine tells the body’s cells to make "spike proteins," similar to what is found on the COVID-19 virus. The immune system responds to the spike proteins by making antibodies. These new antibodies will break down the spike proteins and get rid of them. The new antibodies will protect against COVID-19 infection in the future. The mRNA is broken down by the body shortly after injection and cannot affect the body’s DNA. mRNA vaccines are not live vaccines and cannot cause infection.

Two doses of the vaccine are required for full protection, given at a minimum of 21 days apart. It can be given to individuals born 2009 and older. In trials, the vaccine was 95% effective at preventing symptoms of the COVID-19 virus for those 16 years and older; the vaccine was 100% effective for those 12 to 15 years old. Individuals may not be optimally protected until up to two weeks after their second dose of vaccine. It is essential to complete the vaccine series for best protection. Third doses are available for eligible populations.

There is a small chance that you may still get COVID-19 after being vaccinated. It is important to continue to follow public health measures such as physical distancing, wearing a mask, and staying home if you are sick. Health care workers and other staff must still wear personal protective equipment (PPE) even after they have been vaccinated.

The Pfizer vaccine, like all vaccines, may cause side effects in some people. Symptoms are usually mild and resolve after a few days. Some of the symptoms are part of the body’s response to developing immunity to a virus.

The most commonly reported side effects are:

• pain at the injection site
• swelling, and colour changes in the skin (for example, red, purple) at the injection site
• tiredness
• headache
• muscle or joint pain
• chills
• mild fever

Ongoing studies on the COVID-19 vaccines have found that serious side effects are extremely rare.

Very rare cases of myocarditis (inflammation of the heart muscle) and pericarditis (inflammation of the lining around the heart) following vaccination with COVID-19 mRNA vaccines have been reported. These cases have been reported most frequently in adolescents and younger adults under 30 years of age, more frequently in males compared to females, usually within a week after vaccination, and more frequently after the second dose. These individuals tend to recover quickly.

Individuals should seek medical attention right away if they develop any of the following symptoms after receiving the Pfizer vaccine:

• chest pain
• shortness of breath
• feelings of a fast beating, fluttering or pounding heart

The second dose in the mRNA COVID-19 vaccination series should be deferred in individuals who experience myocarditis or pericarditis following the first dose of an mRNA COVID-19 vaccine, until more information is available.

As a precaution, children who experience myocarditis and/or pericarditis after a first dose of the vaccine should wait to get a second dose until more information is available. Children who have a history of myocarditis unrelated to COVID-19 vaccination should consult their clinical care team for individual considerations and recommendations. If they are no longer under active care for myocarditis, they may receive the vaccine. Caregivers should be advised to seek medical attention for children if they develop symptoms including chest pain, shortness of breath, or palpitations following receipt of a COVID-19 vaccine.

Learn more about Myocarditis and Pericarditis (PDF file).

In rare cases, serious allergic reactions (anaphylaxis) can occur. Allergic reactions can be treated and are usually temporary. Seek medical attention if you have trouble breathing, have hives or swelling of the mouth and throat or a high fever (over 40 degrees C or 104 degrees F). Vaccine side effects will continue to be monitored as people receive the vaccine. If you get a reaction to the vaccine, contact your health care provider who will report the side effect directly to public health. Public health will keep track of the reported side effects to make sure the vaccine continues to be safe.

As of August 18, 2021, the Province extended eligibility for the Pfizer-BioNTech COVID-19 vaccine (external link) to include anyone born in 2009 or older who do not have any contraindications.

On September 29, 2021, the Province issued a recommendation that Pfizer vaccine (external link) be the preferred COVID-19 vaccine for individuals aged 18-24 years old.

Do not get the Pfizer-BioNTech vaccine if you:

• Have a fever, are sick with COVID-19 symptoms, currently have COVID-19 or have been instructed to self-isolate.
• Have an allergy to an ingredient in the vaccine or have had a previous severe reaction to this vaccine.
  • Visit Health Canada’s webpage for Pfizer-BioNTech vaccine ingredients (external link)

It is strongly recommended that you speak with your treating health care provider if you have an autoimmune condition or immunodeficiency condition and are receiving any of the following treatments:

• Have an autoimmune condition or immunodeficiency condition and are receiving any of the following treatments:
  • stem cell therapy
  • CAR-T therapy
  • chemotherapy
  • immune checkpoint inhibitors
  • monoclonal antibodies (e.g., rituximab) and other targeted agents (e.g., CD4/6 inhibitors, PARP inhibitors etc.)

You may choose to consult with your treating health care provider prior to vaccination if you:

• have an autoimmune condition or immunodeficiency condition but are not receiving any of the above treatments
• have a history of allergic reactions not related to the mRNA vaccine
• are pregnant or breastfeeding

The Moderna COVID-19 vaccine uses a method called messenger RNA (mRNA) technology. The mRNA in the vaccine tells the body’s cells to make "spike proteins," similar to what is found on the COVID-19 virus. The immune system responds to the spike proteins by making antibodies. These new antibodies will break down the spike proteins and get rid of them. The new antibodies will protect against COVID-19 infection in the future. The mRNA is broken down by the body shortly after injection and cannot affect the body’s DNA. mRNA vaccines are not live vaccines and cannot cause infection.

Two doses of the vaccine are required for full protection, given at a minimum of 28 days apart. It can be given to people 18 years of age and older. At this time, there is no information on the long-term protection with this vaccine. In trials, the vaccine was 95% effective at preventing symptoms of the COVID-19 virus. Third doses are available for eligible populations.

There is a small chance that you may still get COVID-19 after being vaccinated. It is important to continue to follow public health measures such as physical distancing, wearing a mask, and staying home if you are sick. Health care workers and other staff must still wear personal protective equipment (PPE) even after they have been vaccinated.

The Moderna vaccine, like all vaccines, may cause side effects in some people. Symptoms are usually mild and resolve after a few days. Some of the symptoms are part of the body’s response to developing immunity to a virus.

The most commonly reported side effects are:

• pain at the injection site
• swelling, and colour changes in the skin (for example, red, purple) at the injection site
• tiredness
• headache
• muscle or joint pain
• chills
• mild fever

Ongoing studies on the COVID-19 vaccines have found that serious side effects are extremely rare.

Very rare cases of myocarditis (inflammation of the heart muscle) and pericarditis (inflammation of the lining around the heart) following vaccination with COVID-19 mRNA vaccines have been reported. These cases have been reported most frequently in adolescents and younger adults under 30 years of age, more frequently in males compared to females, usually within a week after vaccination, and more frequently after the second dose. These individuals tend to recover quickly.

Individuals should seek medical attention right away if they develop any of the following symptoms after receiving the Moderna vaccine:

• chest pain
• shortness of breath
• feelings of a fast beating, fluttering or pounding heart

The second dose in the mRNA COVID-19 vaccination series should be deferred in individuals who experience myocarditis or pericarditis following the first dose of an mRNA COVID-19 vaccine, until more information is available.

As a precaution, children who experience myocarditis and/or pericarditis after a first dose of the vaccine should wait to get a second dose until more information is available. Children who have a history of myocarditis unrelated to COVID-19 vaccination should consult their clinical care team for individual considerations and recommendations. If they are no longer under active care for myocarditis, they may receive the vaccine. Caregivers should be advised to seek medical attention for children if they develop symptoms including chest pain, shortness of breath, or palpitations following receipt of a COVID-19 vaccine.

Learn more about Myocarditis and Pericarditis (PDF file).

Speak with your health care professional about any serious allergies or health conditions before receiving the Moderna COVID-19 vaccine.

Vaccine side effects will continue to be monitored as people receive the vaccine. If you get a reaction to the vaccine, contact your health care provider who will report the side effect directly to public health. Public health will keep track of the reported side effects to make sure the vaccine continues to be safe.

The Moderna COVID-19 vaccine is available to anyone over the age of 18 who do not have contraindications.

Out of an abundance of caution, the Province has issued a recommendation for the use of the Pfizer vaccine (external link) for individuals aged 18-24 years old. Individuals aged 18 to 24 may choose to receive Moderna with informed consent.

Do not get the Moderna vaccine if you:

• Have a fever, are sick with COVID-19 symptoms, currently have COVID-19 or have been instructed to self-isolate.
• Have an allergy to an ingredient in the vaccine or have had a previous severe reaction to this vaccine.
  • Visit Health Canada’s webpage for a list of Moderna vaccine ingredients (external link)

It is strongly recommended that you speak with your treating health care provider if you have an autoimmune condition or immunodeficiency condition and are receiving any of the following treatments:

• Have an autoimmune condition or immunodeficiency condition and are receiving any of the following treatments:
  • stem cell therapy
  • CAR-T therapy
  • chemotherapy
  • immune checkpoint inhibitors
  • monoclonal antibodies (e.g., rituximab) and other targeted agents (e.g., CD4/6 inhibitors, PARP inhibitors etc.)

You may choose to consult with your treating health care provider prior to vaccination if you:

• have an autoimmune condition or immunodeficiency condition but are not receiving any of the above treatments.
• have a history of allergic reactions not related to the mRNA vaccine
• are pregnant or breastfeeding

The AstraZeneca vaccine is a viral vector vaccine (external link). Unlike the Pfizer-BioNTech and Moderna vaccines which store the instructions to build spike proteins in RNA, the AstraZeneca vaccine uses DNA. The vaccine uses a harmless virus (called an adenovirus) as a delivery system. This is called a viral vector. Once the vaccine containing the viral vector enters the body, the vector virus produces the SARS-CoV-2 spike protein. Just like with the mRNA vaccines, the immune system responds to the spike proteins by making antibodies. These new antibodies will break down the spike proteins and get rid of them. The new antibodies will protect against COVID-19 infection in the future.

DNA is not as fragile as RNA. The viral vector (adenovirus) has a tough protein coat which protects the DNA inside. Therefore, the AstraZeneca vaccine does not need to be kept frozen.

Viral vector technology has been used for over ten years to produce many of the vaccines approved in Canada.

None of the COVID-19 vaccines currently approved by Health Canada use the live virus that causes COVID-19. You cannot get COVID-19 from a vaccine.

Two doses of the vaccine are required, given up to 16 weeks apart. After completing the two-doses, it may take another 14 days to achieve maximum protection against COVID-19. In trials, the vaccine was 81.6% effective at preventing symptoms of the COVID-19 virus. Data from the trials suggests that the vaccine is 100% effective against hospitalization from the COVID-19 disease (22 days after the first dose).

There is a small chance that you may still get COVID-19 after being vaccinated. It is important to continue to follow public health measures such as physical distancing, wearing a mask, and staying home if you are sick. Health care workers and other staff must still wear personal protective equipment (PPE) even after they have been vaccinated.

The AstraZeneca vaccine, like all vaccines, may cause side effects in some people. Symptoms are usually mild and resolve after a few days. Some of the symptoms are part of the body’s response to developing immunity to a virus.

The most commonly reported side effects are:

• pain at the injection site
• swelling, and colour changes in the skin (for example. red, purple) at the injection site
• tiredness
• headache
• muscle or joint pain
• chills
• mild fever.

Ongoing studies on the COVID-19 vaccines have found that serious side effects are extremely rare.

Vaccine-Induced Immune Thrombotic Thrombocytopenia (VITT)

Very rarely, the AstraZeneca vaccine has been linked to a rare form of blood clot after vaccination.

Experts are calling this Vaccine-Induced Immune Thrombotic Thrombocytopenia (VITT). These blood clots:

• typically occur 4 to 28 days after vaccination;
• are associated with low platelets (tiny blood cells that help form blood clots to stop bleeding); and
• seem to be rare.

It is thought that the vaccine causes an immune reaction that produces antibodies which activates platelets, cells in our blood that form blood clots.

VITT can usually be treated. Individuals should seek immediate medical attention if they develop any of these symptoms after being vaccinated with the AstraZeneca:

• shortness of breath
• chest pain
• leg swelling or pain
• persistent abdominal (belly) pain
• skin bruising (other than at site of vaccination)
• red or purple spots or blood blisters under the skin
• sudden onset of severe or persistent worsening headaches
• blurred vision
• double vision
• confusion or seizures
• difficulty speaking or moving part of the body

Individuals who experienced rare blood clots with unusual platelets following their first dose of the AstraZeneca COVID-19 vaccine should not receive a second dose of any version of the AstraZeneca vaccine.

Capillary leak syndrome

Very rare cases of capillary leak syndrome, a condition that causes fluid leakage from small blood vessels (capillaries), have been reported after vaccination with AstraZeneca vaccine. Symptoms are often linked with feeling faint (due to low blood pressure). People with a history of capillary leak syndrome should not receive the AstraZeneca/COVISHIELD COVID-19 vaccine.

Individuals should be informed of the risks and benefits of their vaccine choices.

For more information on the safety of the AstraZeneca vaccine, please read Health Canada’s website (external link).

Getting the AstraZeneca vaccine for your first dose was the right thing to do. NACI, Health Canada and the Ontario government continue to emphasize that the AstraZeneca vaccine provides good protection against infection and very good protection against severe disease and hospitalization.

With informed consent, individuals who received AstraZeneca for their first dose can choose to receive a second dose of AstraZeneca or an mRNA vaccine (Pfizer or Moderna) at an eight to 12-week interval. While a 12-week interval has been show to provide more protection, residents may choose to receive their second dose sooner to have increased protection provided by receiving a second dose earlier.

• Mixing vaccines
  • Studies have shown that mixing COVID-19 vaccine types is safe and provides good protection.
• Side effects
  • It is common with any vaccine to have mild, short-term side effects such as a sore arm, tiredness, headache, fever or sore muscles.
  • The risk of mild, short-term side effects may be higher after receiving an mRNA vaccine as a second dose.
• Blood clots
  • mRNA vaccines have not been shown to cause blot clots.
• Vaccine intervals
  • After a first dose of the AstraZeneca vaccine, you will need to wait a minimum of 8 weeks for a second dose of an AstraZeneca or mRNA vaccine.
• Getting a second dose is important
  • If you are not fully vaccinated you are still at risk of serious illness from COVID-19.
  • Getting a second dose of any COVID-19 vaccine as early as possible will provide the best protection against COIVD-19 and the variants.

Scheduling your appointment for your second dose is vital.

If you would like to get AstraZeneca for your second dose, contact the pharmacy or healthcare provider where you got your first dose to book an appointment.

If you would prefer to have an mRNA vaccine, you can book your second dose appointment through our online booking system or through a participating pharmacy (external link).

The following resources can help you make an informed decision as to which COVID-19 vaccine is right for you:

• “I got AstraZeneca for my first dose. Which vaccine should I get for my second?” A guide to help you make an informed decision about your second COVID-19 vaccination (external PDF)
• Get your second dose of COVID-19 Vaccine (PDF file)

The AstraZeneca COVID-19 vaccine has been approved by Health Canada for individuals over the age of 18 who do not have contraindications.

Do not get the AstraZeneca vaccine if you:

• Have a fever, are sick with COVID-19 symptoms, currently have COVID-19 or have been instructed to self-isolate.
• Have an allergy to an ingredient in the vaccine or have had a previous severe reaction to this vaccine.
  • Visit Health Canada’s webpage for a list of Pfizer-BioNTech vaccine ingredients (external link)

It is strongly recommended that you speak with your treating health care provider if you have an autoimmune condition or immunodeficiency condition and are receiving any of the following treatments:

• Have an autoimmune condition or immunodeficiency condition and are receiving any of the following treatments:
  • stem cell therapy
  • CAR-T therapy
  • chemotherapy
  • immune checkpoint inhibitors
  • monoclonal antibodies (e.g., rituximab) and other targeted agents (e.g., CD4/6 inhibitors, PARP inhibitors etc.)

You may choose to consult with your treating health care provider prior to vaccination if you:

• have an autoimmune condition or immunodeficiency condition but are not receiving any of the above treatments.
• have a history of allergic reactions, or;
• are pregnant or breastfeeding

Additional information will be posted as it is released from Health Canada.

The Janssen vaccine is a viral vector vaccine (external link). Unlike the Pfizer-BioNTech and Moderna vaccines which store the instructions to build spike proteins in RNA, the Janssen vaccine uses DNA. The vaccine uses a harmless virus (called an adenovirus) as a delivery system. This is called a viral vector. Once the vaccine containing the viral vector enters the body, the vector virus produces the SARS-CoV-2 spike protein. Just like with the mRNA vaccines, the immune system responds to the spike proteins by making antibodies. These new antibodies will break down the spike proteins and get rid of them. The new antibodies will protect against COVID-19 infection in the future.

DNA is not as fragile as RNA. The viral vector (adenovirus) has a tough protein coat which protects the DNA inside. Therefore, the Janssen vaccine does not need to be kept frozen.

Viral vector technology has been used for over ten years to produce many of the vaccines approved in Canada.

None of the COVID-19 vaccines currently approved by Health Canada use the live virus that causes COVID-19. You cannot get COVID-19 from a vaccine.

A single dose of the vaccine is required. It can be given to people over 18 years of age. In trials, the vaccine was 66% effective at preventing moderate to severe COVID-19.

There is a small chance that you may still get COVID-19 after being vaccinated. It is important to continue to follow public health measures such as physical distancing, wearing a mask, and staying home if you are sick. Health care workers and other staff must still wear personal protective equipment (PPE) even after they have been vaccinated.

Common side effects following administration of the Janssen vaccine are typically mild or moderate and are common of many vaccines, including:

• pain at the site of injection
• body chills
• feeling tired
• feeling feverish

These are common side effects of vaccines and do not pose a risk to health. As with all vaccines, there’s a chance that there will be a serious side effect, but these are rare. A serious side effect might be something like an allergic reaction.

Safety Concerns: Vaccine-Induced Thrombotic Thrombocytopenia (VITT)

Individuals should seek medical attention if they develop the following symptoms four or more days after receiving the Janssen (COVISHIELD) COVID-19 vaccine:

• shortness of breath
• chest pain
• leg swelling
• persistent abdominal (belly) pain
• neurological symptoms (such as sudden onset of severe or persistent worsening headaches or blurred vision)
• skin bruising or tiny blood spots under the skin beyond the site of the injection

For more information on the safety of the Janssen (COVISHIELD) vaccine, please read Health Canada’s website (external link).

The Janssen COVID-19 vaccine is approved for use in people 18 years of age and over.

Additional information will be posted as it is released from Health Canada.

If you have questions or concerns about getting vaccinated for COVID-19, you can:

• speak with your primary health care provider (for example, family doctor, nurse practitioner, midwife); or
• connect by phone with a trained health care provider who can offer accurate information on getting vaccinated for COVID-19 as listed below

• Ontario Ministry of Health
  • COVID-19 Vaccine Information sheet (external PDF)
  • COVID-19 Vaccines for Ontario Youth (external link)
  • Questions about COVID-19 vaccines? Here are some answers. (external PDF)
• Government of Canada
  • Ask the experts video series: COVID-19 vaccine questions (external video link)
  • The facts about COVID-19 Vaccines (external link)
  • COVID-19 vaccines and Indigenous peoples (external link)
• Other
  • About Kids Health: COVID-19 Vaccines (external link)
  • Caring for Kids: COVID-19 vaccines for children and youth (external link)
  • Immunize Canada: COVID-19 Information for the public (external link)
  • National Institute on Aging: COVID-19 Vaccines – What Older Canadians Need to Know (external PDF)
  • Society of Obstetricians and Gynaecologists of Canada: COVID-19 Vaccination in Pregnancy (external link)
  • Women’s College Hospital: COVID-19 Vaccine: Multi-language Information (external link)