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AstraZeneca Vaccine

The AstraZeneca COVID-19 vaccine (ChAdOx1-S) was approved for use in Canada on February 26, 2021. Canada has authorized two manufacturers of this vaccine:

  • AstraZeneca (brand name AstraZeneca COVID-19 Vaccine)
  • Verity Pharmaceuticals and Serum Institute of India (SII) in collaboration with AstraZeneca (brand name COVISHIELD Vaccine)

These vaccines are the first viral vector-based vaccines authorized in Canada to prevent COVID-19.

What are the ingredients in the AstraZeneca COVID-19 Vaccine?

Medicinal ingredient: Adenovirus vector vaccine (ChAdOx1-S)

Non-medicinal ingredients:

  • ethanol
  • disodium edetate dihydrate (EDTA)
  • L-histidine
  • L-histidine hydrochloride monohydrate
  • magnesium chloride hexahydrate
  • polysorbate 80
  • sodium chloride
  • sucrose
  • water for injection

Do NOT take the AstraZeneca vaccine if you:

  • are hypersensitive or allergic to any of the ingredients in the vaccine.
  • have had a severe reaction (anaphylaxis) to a previous dose of the vaccine.

If you have any symptoms that could be due to COVID-19, talk with your healthcare professional about your symptoms and getting a COVID-19 test.

Who can receive the AstraZeneca vaccine?

Health Canada has approved the vaccine for people who are 18 years of age and older. Its safety and effectiveness in people younger than 18 years of age have not yet been established.

The National Advisory Committee on Immunizations (NACI) has updated the recommendations on as a result of rare condition of blood clot formation following vaccination. While previous recommendation included offering the vaccine to adults 55 years of age and older, the latest recommendation, based on current evidence, is that the use of AstraZeneca vaccine may now be offered to adults 30 years of age and older. However, in Ontario, it is individuals 40 years of age and older who are eligible to receive this vaccine.

Can I receive the vaccine if I am pregnant?

Pregnant individuals may choose to receive the vaccine at any time during their pregnancy. However, essential consideration should be made for those in the later stages of their pregnancy.

It is recommended, but not required, that pregnant individuals have discussion with their treating health care provider, or with a health care provider familiar with their pregnancy, that includes:

  • a review of the potential risks and benefits of the vaccine,
  • a review of the risk of acquiring a COVID-19 infection during pregnancy,
  • a review of the potential risks /consequences associated with a COVID-19 infection during pregnancy, and
  • an acknowledgment of the limited evidence from clinical trials of COVID-19 vaccines in the pregnant population.  

Please see the COVID-19 Vaccination Recommendations for Special Populations for further details on COVID-19 vaccination for pregnant individuals.

Please Note:

  • A letter from a health care provider is not required for vaccination.
  • The extended dose interval of 16 weeks remains appropriate for this population.

Can I receive the AstraZeneca vaccine if I am immunocompromised by disease or treatment?

  • Speak with your health care provider to receive informed counselling about COVID-19 vaccination. The counselling session should include a review of the risks and benefits of the vaccine, a review of the potential risks/consequences of a COVID-19 infection, a review of the risk of acquiring a COVID infection, an acknowledgment of the insufficiency of evidence for the use of current COVID-19 vaccines in these special populations
  • When you go for your vaccination appointment, you will have to verbally confirm that you have received proper counselling from your health care provider, prior to vaccination.

How many doses of the AstraZeneca vaccine will I need?

You will require 2 doses of the vaccine. It is recommended that the two doses be given between 4 and 12 weeks apart.

How do viral vector-based vaccines work?

COVID-19 viral vector-based vaccines use a harmless virus (adenovirus) which is modified and used as a delivery system for making the SARS-CoV-2 spike protein. The vector virus used is not the virus that causes COVID-19 infection (SARS-CoV-2).

Adenovirus is a common virus that can cause cold-like symptoms, but it is safe to use as it has been modified and cannot cause infection.

Once immunized, the virus vector enters cells and provides instructions to make the SARS-CoV-2 spike protein. Like with natural infection, when the immune system is exposed to parts of the spike protein an immune response is initiated. This leads to the creation of antibodies. These antibodies allow the immune system to recognise, respond and protect the person if exposed to COVID-19 virus at a later time.

After vaccination, how long will it take for protection against COVID-19?

Immunity develops over time. It takes about 2 weeks to develop significant protection against COVID-19. For the greatest protection, you will need the second dose. 

In clinical studies, the average efficacy of the AstraZeneca vaccine against symptomatic COVID-19 infection was 62% beginning two weeks after the second dose.

How long does immunity from the AstraZeneca vaccine last?

Like other COVID-19 vaccines, the length of immunity from the Astrazeneca vaccine remains unknown. Currently, there is no evidence to suggest the need for booster doses of COVID-19 vaccine, after the two doses are complete. Research is ongoing.

How is the AstraZeneca vaccine administered?

COVID-19 vaccines are given as an intramuscular (IM) injection into the deltoid muscle (upper arm).

What are the possible side effects?

The side effects are similar to other vaccines. They are generally mild to moderate and are resolved within a few days. They include things like pain at the injection site, body chills, feeling tired, and feeling feverish. These are common side effects of vaccines, and do not pose a risk to health. With all vaccines, there is a chance of a serious side effect such as an allergy reaction, although these are rare. Speak with your health care provider before vaccination if you have a health condition or a serious allergy.

Is the vaccine safe?

Health Canada has completed a rigorous scientific review of the available medical evidence to assess the safety of the AstraZeneca COVID-19 Vaccine. The vaccine is safe and effective, and no major safety concerns have been identified. There will be continued monitoring for the safety and efficacy of COVID-19 vaccines after authorization. Find more information on the safety of the vaccine on the Government of Ontario website.

Vaccine-Induced Immune Thrombotic Thrombocytopenia (VITT), blood clot formation along with low levels of blood platelets following vaccination is a rare adverse event associated with the AstraZeneca vaccine. There is a very small risk that these rare blood clots will occur following immunization with the AstraZeneca COVID-19 vaccine, occurring in 1 in 250,000 to 1 in 500,000 people.

Treatment for the potential rare side effect of blood clot formation after receiving the AstraZeneca vaccine is available. Individuals should seek urgent medical attention if any of the following symptoms develop following vaccination:

  • Shortness of breath
  • Chest pain
  • Leg swelling
  • Persistent abdominal pain
  • Neurologic symptoms (e.g. severe and persistent worsening headaches or blurred vision)
  • Skin bruising or tiny blood spots under the skin

Health Canada has a robust vaccine safety system which begins at the vaccine development stage and continues even after vaccines are approved. It is due to this strong system that Health Canada was able to recognize the potential risk of rare blood clots that have occurred following vaccination with the AstraZeneca COVID-19 vaccine and take measures to review all available scientific data to refine recommendations, notify the public and healthcare providers to ensure transparency of this possible risk, and ensure ongoing safety of the vaccine.

As with all decisions in life one must balance risk and benefit. When making an informed decision about getting the AstraZeneca COVID-19 vaccine, it is important to consider that the risks of COVID-19 infection strongly outweigh the risks of the vaccine, this is especially true now that community spread of COVID-19 variants is evident across the district. The COVID-19 variants of concern increase the risk of infection, hospitalization, and death.

Consider these facts when making an informed decision about receiving this vaccine:

  • There is only a very small risk that these rare blood clots will occur following immunization with the AstraZeneca COVID-19 vaccine, occurring in 1 in 250,000 to 1 in 500,000 people.
  • According to Thrombosis Canada, each year the general population’s risk of developing a blood clot is 1 or 2 out of 1,000 people (0.1%-0.2%).
  • Data from Thrombosis Canada indicates that COVID-19 infection is linked to blood clots:
    • The risk for those with COVID-19 infection that do not require hospitalization is about 1% or 1 in 100 people.
    • About 5% (or 1 in 20) of individuals with COVID-19 infection requiring hospitalization on a standard ward or medical floor, and
    • Individuals admitted to intensive care units (ICU), on life support, up to 20% (1 in 5 people).

What if I miss my second dose?

If you forget to go back to your healthcare professional at the scheduled time for your next dose, ask your healthcare professional for advice. It is important that you return for your second injection, or the vaccine may not work as well.

After Vaccination

Even after getting your second dose, continue to follow public health measures like wearing a mask, physical distancing and washing your hands often. The vaccine is an additional tool in our fight against COVID-19. It is unknown how long immunity from the vaccine will last. In addition, not everyone is able to get the vaccine for various reasons. We must continue to follow public health measures to slow the spread of COVID-19. Monitor for symptoms of COVID-19 and get tested if symptoms present. There is preliminary evidence that the AstraZeneca vaccine may reduce asymptomatic infection, but the evidence is insufficient at this time to recommend stopping public health measures after vaccination.

Is AstraZeneca better than other COVID-19 vaccines?

All COVID-19 vaccines are good, and all vaccines will help fight the COVID-19 pandemic.

The authorization of additional vaccines in Canada to fight the pandemic can only help and provide additional support to respond to the pandemic as quickly as possible.

There are 4 vaccines approved for use in Canada and each report a different efficacy rate. The efficacy of different vaccines cannot be directly compared. Each vaccine was studied in a different clinical trial which were conducted at different times, using different populations and conditions. The authorized COVID-19 vaccines have not been compared in clinical trials.

Having additional vaccines authorized for use in Canada will provide the opportunity to better meet the vaccine dose volume needs so that more people can be vaccinated and protected against COVID-19 sooner.

Viral vector-based vaccines have the advantage of being easily transported and stored as opposed to mRNA vaccines.