COVID-19 Vaccine-Specific Information

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The short answer to the question is YES, the individual can still get the COVID-19 vaccine. Here is some additional information about what we know about breastfeeding and the COVID-19 vaccine:

  • Clinical vaccine trials excluded lactating people, so there is currently very limited data on safety and effects of COVID-19 vaccination in infants that are breastfed. 

  • Based on real world data indicating COVID-19 vaccines are safe during breastfeeding, NACI’s recommendation for COVID-19 vaccination in breastfeeding individuals is a complete vaccine series with an mRNA COVID-19 vaccine.

  • As per the Canadian Immunization Guide, routinely recommended vaccines can be safely administered to breastfeeding individuals. There are limited data available regarding the effects of immunization of breastfeeding individuals on their infants; however, there have been NO reported adverse events related to administration of routine vaccines. There is no evidence that immunization during breastfeeding will adversely influence the maternal or infant immune response.  There may be some concern with live vaccines, but the COVID-19 vaccine is not a live vaccine.

  • The components of the COVID-19 vaccines are not expected to enter the breast milk or be absorbed by the infant. If any small amounts of vaccine ingredients did enter the breast milk, they would most likely be destroyed in the baby’s stomach. In case you get asked, mRNA does not enter the breastmilk.

  • What is passed along to an infant of a breastfeeding individual that is vaccinated is antibodies.  Individuals who receive an mRNA vaccine have marked increases in milk antibodies against SARS CoV-2 that potentially protect breastfed infants from infection. More data are needed to determine what protection these antibodies may provide to the infant.

  • In studies of mRNA vaccines given to breastfeeding people, no serious adverse effects were reported in infants.  Some participants reported irritability, poor sleep, drowsiness in their infants, but it was not shown that these side effects were caused by the vaccine.

  • In these same studies, breastfeeding individuals also reported minor effects on lactation and breastmilk (decreased supply, colour change) but these reports were uncommon, and once again, causality was not necessarily proven. 




26 Oct 2021

We were not able to find any information that suggests being on clozapine would be a contraindication to receiving the COVID-19 vaccine. However, the following information may be helpful for clinicians and patients on clozapine to consider:

  • There is a single case report of increased clozapine levels and toxic effects in a patient on clozapine that received Pfizer-BioNTech Comirnaty™, but a causal relationship was neither determined nor ruled out. This would not be a reason to avoid vaccination, but may suggest increased monitoring for clozapine adverse effects following vaccination and clozapine drug level when indicated.(1)
  • There are several case studies indicate that COVID-19 infection can be associated with increased clozapine levels.(2,3)  This may be attributed to infection-related inflammation inhibiting cytochrome P450 1A2 (CYP1A2), which then slows clozapine metabolism.(4)  This does not speak to any concern about giving a COVID-19 vaccine, but may explain the mechanism of increased drug levels.

Based on available information, and taking in to consideration the risk versus benefit, clozapine therapy would not be a contraindication to receiving the COVID-19 vaccine. It is important to ensure that the patient is aware of potential adverse effects, and monitor appropriately. 

  1. Thompson D, Delorme CM, White RF, Honer WG. Elevated clozapine levels and toxic effects after SARS-CoV-2 vaccination. J Psychiatry Neurosci. 2021 Mar 5;46(2):E210-E211. doi: 10.1503/jpn.210027. PMID: 33667055; PMCID: PMC8061735.
  2. Cranshaw T, Harikumar T. COVID-19 infection may cause clozapine intoxication: case report and discussion. Schizophr Bull 2020;46:751.
  3. Dotson S, Hartvigsen N, Wesner T, et al. . Clozapine toxicity in the setting of COVID-19. Psychosomatics 2020;61:577–8.
  4. Clark SR, Warren NS, Kim G, et al. . Elevated clozapine levels associated with infection: a systematic review. Schizophr Res 2018;192:50–6.

20 May 2021

Cases of Vaccine-induced Immune Thrombotic Thrombocytopenia (VITT) have been reported following viral vector vaccines and usually occur between 4 and 28 days after receipt.

Individuals should be monitored for symptoms -  such as persistent and severe headache, vision changes, seizures and other symptoms that resemble a stroke, such as weakness or numbness of the arms or legs, shortness of breath, abdominal or chest pain, swelling and redness in a limb and pallor and coldness in a limb, - for up to 42 days following a viral vector vaccine dose. If any of these symptoms present, individuals should seek immediate medical attention.

The rate of VITT is estimated to be between 1 per 26,000 and 1 per 100,000 persons vaccinated with a first dose of AstraZeneca Vaxzevria™. As of May 12, 2021, PHAC has estimated the rate of VITT in Canada to be 1 in 83,000 doses administered, however, as investigations continue, this rate could be as high as 1 in 55,000.

The frequency of VITT following a second dose of AstraZeneca Vaxzevria™ is currently reported as approximately 1 per 600,000 individuals vaccinated with a second dose but continues to evolve, based on vaccine safety surveillance data from the United Kingdom.

Current Canadian COVID-19 vaccination guidelines do not include delaying COVID-19 vaccination in patients that have recently completed antiviral therapy.

Antivirals prevent further replication of viruses. mRNA vaccines and non-replicating viral vector vaccines do not contain live replicating virus so we would not expect a diminished response to the vaccine with prior or recent receipt of anti-viral medication.

For reference, there is no reason to withhold inactivated influenza and varicella* vaccines for patients taking antivirals or antibacterials.

*inactivated varicella= Shingrix®
26 May 2021
It is recommended to receive two doses of the same mRNA vaccine (either 2 doses of Pfizer-BioNTech Comirnaty™ or 2 doses of Moderna Spikevax™).
  • When the same mRNA COVID-19 vaccine product is not readily available, or is unknown, another mRNA COVID-19 vaccine can be used. However, this may have implications for international travel. 

If the 1st dose was AstraZeneca Vaxzevria™, it is recommended to receive an mRNA vaccine for the 2nd dose.

If mRNA vaccine is not an option (e.g. severe allergy to ingredients of the vaccines), AstraZeneca Vaxzevria™ may be used; AstraZeneca Vaxzevria™ is only available through Public Health.


14 Feb 2022

All COVID-19 vaccines are to be injected intramuscularly and the deltoid is the preferred site.

There may be instances when the deltoid sites cannot be used or are inaccessible. Examples may include individuals with:

  • Poor lymphatic circulation
    • These may include individuals with local lymphedema, upper limb amputation, axillary lymph node removal (which sometimes accompanies mastectomy), lymphangioma, arteriovenous (A-V) fistula
  • Poor muscle mass
  • Active cutaneous conditions (e.g. psoriasis plaques, inflammation, scars on the injection site)
  • Pain at the injection site

If only one deltoid is affected, use the other deltoid.

If both deltoid sites are unsuitable for IM injection, the vastus lateralis is an alternative site.

  • Landmarking for vastus lateralis
    • With the individual in the seated position, visually divide the length of the muscle from the greater trochanter of the femur to the lateral border of the kneecap into thirds.
    • Visually divide the width of the outer thigh in two with a horizontal line.
    • The injection site is in the middle third, just above the horizontal line.
      • See the vastus lateralis landmarking demonstration video. 
  • Needle length
    • Needle length for IM injections is based on age, muscle mass and amount of subcutaneous tissue. For both deltoid and vastus lateralis:
      • 18 years and older: 1” to 1.5” (1” most common)
      • 5 to 17 years old: 1” (1.5” for heavier children)
Dorsogluteal is NOT an acceptable alternative site.
  • This injection site is not used for active immunization because it is less immunogenic for vaccines.

18 Jun 2021

Approval for the vaccines is following the usual processes to ensure safety and efficacy. The process could be expedited because:

  • more resources were made available
  • resources / work were shifted from other projects to focus on the vaccine
  • global agencies have been working together and sharing data
  • trials were undertaken in areas with high risk of COVID-19 infection so it didn't take long to accrue data
  • The two mRNA vaccines have been shown to be ~95% effective beginning one week (Pfizer-BioNTech Comirnaty™) to two weeks (Moderna Spikevax™) after the 2nd dose. Note: The stated effectiveness of both of these vaccines are for the dominant strains of the virus and do not yet account for the variants that have popped up since.
    • Individuals may not be optimally protected until 1-2 weeks after receiving the second dose.  
    • Maximum duration of immunity is not yet known; data continue to be collected.
  • AstraZeneca Vaxzevria™ and COVISHIELD have demonstrated an average efficacy of ~62% effective in those 18-64 years of age. 
    • The protection offered by the first dose of the viral vector vaccine is comparable to the efficacy observed after the second dose, with protection lasting until the second dose is administered (up to 12 weeks later).
    • Maximum duration of immunity is not yet known; data continue to be collected.
  • The Janssen (Johnson & Johnson) COVID-19 vaccine had a 72% efficacy in preventing COVID infections after 28 days in the company’s U.S. trials. Note: The efficacy dropped to 66% when averaging in results from other global trials, including a South African study that factored in more transmissible variants of the COVID virus.

Short-term adverse effects are similar to those experienced with other vaccines and no safety concerns have been identified. Long-term adverse effects are not known, though most adverse effects of vaccines appear fairly soon after the dose.

In clinical trials of mRNA vaccines, some adverse events, including fever, are more frequent after the second dose; this was not the case with AstraZeneca Vaxzevria™.

19 Mar 2021

A traditional vaccine delivers the antigen directly by using a weakened form of the virus, while the mRNA vaccine gives the "code" for the body to make the antigen. This then triggers the immune response to make antibodies, which in turn help to fight the virus if exposed at a later date.


19 Mar 2021

Viral vector-based vaccines use a harmless virus, such as an adenovirus, as a delivery system. This “vector” virus is not the virus that causes COVID-19. Adenoviruses are among the viruses that can cause the common cold. There are many different types of adenoviruses, and many have been used as delivery systems for other vector-based vaccines for decades.

When a person is given the vaccine, the vector virus contained within the vaccine produces the SARS-CoV-2 spike protein. This protein is found on the surface of the virus that causes COVID-19. This protein will not make you sick. It does its job and goes away. Just like with a natural infection, when the immune cells in the body are exposed to parts of the virus in a vaccine, antibodies are developed and immune cells are primed to respond to prevent infection. 


19 Mar 2021

NOTE: The COVISHIELD version of this vaccine provided a temporary supply to Canadians and is no longer authorized.

Canada has authorized 2 manufacturers of the ChAdOx1-S vaccine:

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

Vaxzevria™ COVID-19 Vaccine (manufactured by AstraZeneca) and COVISHIELD (manufactured by Serum Institute of India) are ChAdOx1-S recombinant vaccines developed by AstraZeneca and Oxford University. Health Canada has reviewed the manufacturing information for these vaccines and found them to be comparable.


26 Oct 2021

No. The mRNA only goes into the cytosol of the cell. DNA (genetic information) is found in the nucleus of the cell, which the mRNA never enters.  


19 Mar 2021

Unfortunately, at this time, the duration of protection after receiving one or both doses is unknown. The vaccine clinical trials have only provided us with short-term data; data continue to be collected. 


19 Mar 2021