This article is presented by Firstline, a point of care tool for infectious diseases.

Last updated: April 23, 2021

Contents

Current Canadian Guidance

  • Health Canada has determined that the AstraZeneca vaccine may be associated with extremely rare but severe cases of thrombosis and thrombocytopenia that mimics heparin-induced thrombocytopenia, called VITT (Vaccine-induced Thrombotic Thrombocytopenia) or called VIPIT (Vaccine-Induced Prothrombotic Immune Thrombocytopenia).
  • There are no known risk factors at this time, including age or gender, but an update was made to the Canadian product monograph under the warnings and precautions section indicating that indvidiauls who have experienced cerebral venous sinus thrombosis (CVST) or heparin-induced thrombocytopenia (HIT) should only receive the AstraZeneca/ COVISHIELD COVID-19 vaccine if potential benefits outweigh risks.
  • Health Canada maintains that the AstraZeneca vaccine meets the safety standard for use in Canadians above the age of 18.
  • The independent National Advisory Committee on Immunization (NACI) has recommended that the vaccine may be offered to those above the age of 30 if benefits outweigh the risks, if the risks of Vaccine-Induced Immune Thrombotic Thrombocytopenia (VITT) are clearly explained and understood, and if there is a substantial delay in accessing an mRNA COVID-19 vaccine.
  • Ontario, Manitoba, Alberta, and British Columbia are currently offering the AstraZeneca vaccine to residents over the age of 40, and Quebec is offering this vaccine to those over 45. The precautionary measures that have been put in place since discovery of rare types of blood clots associated with the AstraZeneca COVID-19 vaccine are important aspects of pharmacovigilance. Balancing risks and benefits of an intervention is the cornerstone of healthcare, and as data continues to emerge, NACI and Health Canada will continue to assess overall risk, monitor the global situation, and provide updates to health care providers and the public.

Timeline

If you would like to learn more about the timeline of guidance, public health measures and global response related to this topic, please visit the timeline below.

Overview of Blood Clots Related to Vaccine-Induced Immune Thrombotic Thrombocytopenia (VITT)

On March 18, 2021, the PRAC committee of the European Medicines Agency (EMA) indicated that the AstraZeneca vaccine may be associated with less common types of clots: 18 cases of cerebral venous sinus thrombosis (CVST) and 7 disseminated intravascular coagulation (DIC) out of 20 million people who received the AstraZeneca Vaccine in the UK and EEA. The cases presented with thrombosis and thrombocytopenia (low platelets), similar to heparin induced thrombocytopenia (HIT); however, there was no known exposure to a heparinoid. Below, we are going to briefly touch on each of these specific coagulopathies.

Venous Thromboembolisms The most commonly discussed form of blood clot is venous thromboembolism, or VTE. The Centre for Disease Control (CDC) provides a great overview of VTE and describes this presentation as blood clots in the venous circulation with serious complications occurring when a part of the blood clot breaks off and travels through the bloodstream to cause a pulmonary embolism (PE). Thrombosis Canada provides further guidance on the diagnosis and treatment of deep vein thrombosis (DVT), a subcategorization of VTE. The estimated incidence of DVT in Canada is approximately 1-2 cases per 1000 people per year according to Thrombosis Canada, and approximately one third of those who develop DVT have a complication of symptomatic PE. As detailed above, the PRAC committee of the EMA reported on March 18 2021 that there was no indication that these types of clots were occurring with the AstraZeneca vaccine.

Cerebral Venous Sinus Thrombosis (CVST) Also known as Cerebral Venous Thrombosis, CVST is a rare form of stroke representing 0.5% to 3% of all types of strokes and occurs in the dural sinus veins.¹ Clinically, it is characterized by a highly variable presentation. Young women are more likely to develop CVST as seen in a Dutch cross-sectional study with an average incidence of roughly 1.3 cases per 100,000 person years.² The increased risk in women appears to be primarily driven by oral contraceptive use and pregnancy, though other risk factors such as thrombophilia, malignancy, and infection have also been identified.¹,³ At this time, none of these risk factors have been associated as the triggers for CVST episodes seen following administration of the AstraZeneca COVID-19 vaccine.

Disseminated Intravascular Coagulation (DIC) DIC is a systemic process that can cause both uncontrolled bleeding and clotting that can lead to dysfunction of multiple organs.⁴ The typical pathway of DIC involves procoagulant exposure triggering widespread clotting, which in turn consumes clotting factors faster than they can be synthesized; hence why this presentation can also be referred to as consumptive coagulopathy.⁴ Acute DIC can be triggered by infection, occurring in 30 to 50% of severe sepsis, or trauma.⁴ DIC can also occur in about 20% of metastatic cancer or other lymphoproliferative processes as well as in some obstetrical complications.⁴ This presentation is similar to what is seen in the rare cases of clots with the AstraZeneca vaccine; however, DIC is not triggered by an autoimmune process, whereas VITT might be.

Heparin Induced Thrombocytopenia (HIT) A rare limb and life-threatening immune-mediated response to heparin, HIT, is triggered by antibodies which target a complex of Platelet Factor 4 (PF4) and heparin.⁵ Once the antibodies bind this complex, they activate the associated platelets and others nearby, creating a cascade of further platelet activation and thrombin generation.⁵ This cycle causes widespread clotting in both arteries and veins, as well as thrombocytopenia when immune cells begin removing platelets that have been bound by antibodies.⁵ A similar presentation has been proposed and termed spontaneous HIT when observed without known exposure to a heparinoid. Some of these case studies have been seen with infection or suspected glycosaminoglycans released during surgery.⁶ Our current understanding of the clotting disorders following use of the AstraZeneca COVID-19 vaccine is speculating a similar mechanism of pathogenesis and is being termed Vaccine-Induced Immune Thrombotic Thrombocytopenia (VITT).

What is the Proposed Mechanism for Vaccine-Induced Immune Thrombotic Thrombocytopenia (VITT)?

The proposed mechanism of VITT (also known as Vaccine-Induced Prothrombotic Immune Thrombocytopenia, or VIPIT) was initially described in a case series preprint by Greinacher et al., released March 29, 2021 that has now been peer reviewed and published in the NEJM.⁷ VITT is thought to mimic HIT, in absence of heparin, following administration of the AstraZeneca COVID-19 Vaccine. It is hypothesized that vaccination stimulates production of antibodies targeting platelet factor 4 (PF4) leading to platelet activation and a hypercoagulable and thrombocytopenic state.

The study conducted by Greinacher et al. included 11 individuals in Germany and Austria who developed thrombosis or thrombocytopenia after vaccination with the AstraZeneca (ChAdOx1 nCov-19) COVID-19 vaccine.⁷ A standard assay used to detect platelet factor 4 (PF4) heparin antibodies and a modified test to detect platelet-activating antibodies under various different conditions. Of the original sample, 9 were women, age range of 22 to 49 and the thrombotic complications developed 5 to 16 days after receiving the AstraZeneca vaccine. Of those with thrombotic events, 9 were CVST, 5 DIC, 3 splanchnic-vein thrombosis, 3 PEs and 4 had other thromboses. Of these individuals, 6 died. None of these patients received heparin previously. The authors hypothesize that vaccination with the AstraZeneca (ChAdOx1 nCov-19) COVID-19 vaccine may be associated with development of a prothrombotic disorder that resembles HIT with a different serologic profile.

A second study from researchers in Norway reports findings in 5 individuals who presented with venous thrombosis and thrombocytopenia approximately 7 to 10 days after receiving the first dose of the AstraZeneca (ChAdOx1 nCov-19) COVID-19. ⁸All individuals were healthcare workers between the ages of 32 to 54, and 4 of the 5 were female. Four of the 5 individuals presented with cerebral venous thrombosis with intracranial hemorrhage, and 3 of 5 patients had a fatal outcome. Anticoagulation treatment involved varying doses of LMWH in 4 of the individuals and heparin in one. Of the two patients who recovered, anticoagulation was bridged to warfarin. Four of the 5 patients received either prednisolone or methylprednisolone and IVIG.

Interim Guidance for Health Care Professionals on VITT

Dr. Pai et al., from the Ontario Science Table, have created a decision tree type schema for diagnosing and ruling out VITT to act as interim guidance for health care providers. If VITT is suspected, it is recommended to avoid heparin and platelet transfusions. The first line anticoagulation suggested in this guidance are the direct acting oral anticoagulants such as apixaban and rivaroxaban. IVIG is recommended for 2 days in severe or life-threatening blood clots and a consultation to hematology would be vital. The guidance can be found here.

Why the Change in Age Cutoff Over Time?

After a thorough and independent review of pharmacovigilance data, Health Canada concluded on April 14, 2021 that the signal of these rare blood clots is most likely real but the safety of the AstraZeneca vaccine meets strict safety standards for authorization and continued use in Canada for those aged 18 years and older. Furthermore, when considering a risk versus benefit analysis, the benefits of the vaccine at protecting against COVID-19 and its associated risk of morbidity and mortality outweigh the potential risk of these rare types of blood clots.

NACI provides recommendations on use of vaccines in Canada to maximize public health benefits and minimize harms. The current recommendations for the AstraZeneca vaccine take into account the low risk of developing VITT after vaccination, the availability of other COVID-19 vaccines with no safety signals, and the risk of contracting COVID-19 given the evolving epidemic in Canada. NACI currently recommends that the AstraZeneca vaccine be offered only to those above the age of 30 if benefits outweigh the risks of developing VITT or of waiting for an mRNA vaccine. NACI’s original recommendation to suspend use of the AstraZeneca vaccine in those younger than 55 years of age was based on the finding that these rare clotting events were initially identified mostly in women of less than 55 years of age; however, this may have been because the majority of those who received the AstraZeneca vaccine in the EU were female healthcare workers under 55. VITT has since been identified in older individuals, and neither age nor gender are formally identified as risk factors. In contrast, we know that the risks of COVID-19 increases with age; therefore, the risk-benefit analysis changes accordingly.

As the pandemic continues to affect lives of people around the world, a risk versus benefit analysis is being conducted by countries based on the presence of viral spread, current situation, available vaccine supply and other factors. In Canada, the lowering of age cutoff comes after thorough review of evidence to support safety. As more data accumulates and the pandemic progresses, we suspect that changes with respect to eligibility may continue to be made.

It is ultimately up to the provinces and territories to decide how to use the vaccines and whether or not to follow NACI recommendations. Many provinces are battling a third wave with several variants of concern and rising ICU admissions in younger populations. Unlike the mRNA vaccines, the AstraZeneca vaccine’s simple storage requirements allow it to be administered in community pharmacies and doctor’s offices, making it more accessible for many Canadians. Given the low risk of developing VITT, and the benefits of preventing further COVID-19 illness by expanding access to the AstraZeneca vaccine, provinces with high incidence rates of COVID-19 opted to lower the age cutoff for the AstraZeneca vaccine prior to NACI’s updated recommendations.

Monitoring for Signs and Symptoms of Blood Clots

Health Canada, Thrombosis Canada, and the Ontario Science Table provide valuable resources for patients to be able to recognize signs and symptoms of clots. With the proposed mechanism of VITT that has been associated in rare instances with the AstraZeneca vaccine, symptoms began within 4 to 20 days after vaccination. Therefore, if any of the following symptoms are experienced, or if you are concerned, it is important to seek medical care right away.

Signs and symptoms of clots:

  • Shortness of breath or feeling out of breath
  • Chest pain
  • Swelling or pain in abdomen
  • Sudden onset headache
  • Persistent headache
  • Dizziness or lightheadedness
  • New widespread bruises or petechiae (small pinprick spots that may be red, brown, or purple) visible on the skin

Note to our readers Thank you for reading this blog post. We hope it provides a good overview of a snapshot in time about the rare adverse drug reaction (ADR) of thrombosis with thrombocytopenia associated with the AstraZeneca COVID-19 vaccine. New information on this topic will be housed in a future blog resource so as to not create a document that is too large to navigate.

4 Useful Resources

1. VITT (aka VIPIT) - COVID-19 Science Table Brief

2. Thrombosis Canada CLOTS Patient Resources

3. SOGS COVID-19 Resources

4. Communicating risk and benefit analysis of the AstraZeneca COVID-19 Vaccine (University of Cambridge)

Biographies

Dr. Kimberley Gauthier is a Cell Biology Research Fellow in Toronto. She completed her PhD in Cell Biology at McGill University where she specialized in cell signaling, protein trafficking, and developmental genetics. Since January 2021, she has been volunteering alongside scientists and clinicians from COVID-19 Resources Canada as a science communicator for COVID-19 vaccine Q&A town halls hosted for the public. You can follow her on Twitter @thekimgauthier.

Dr. Amir Imani is a clinical pharmacist working in neurological rehabilitation and an instructor at the Leslie Dan Faculty of Pharmacy, where he also received his Doctor of Pharmacy degree. Prior to the pandemic, his projects and research focused on antimicrobial stewardship, demedicalization, and secondary stroke prevention. Since the pandemic, his extra-clinical work has shifted to education regarding COVID-19 therapeutics and vaccines within his hospital. He has also regularly volunteered for COVID-19 Resources Canada as a content expert. You can follow him on Twitter @TheAmirImani.

Dr. Krishana Sankar completed her PhD from the Faculty of Medicine at the University of Toronto where she specialized in cellular & molecular biology and used bioengineering with the aim of improving islet transplantation for type 1 diabetes. She is currently the science communication lead for COVID-19 Resources Canada, Science Advisor for ScienceUpFirst. Dr. Sankar is passionate about countering misinformation and has been dispelling misconceptions around healthcare issues for several years. She has been doing vaccine education outreach to communities in Canada (as an expert volunteer with COVID-19 Resources Canada) and Guyana. You can follow her on Twitter @KrishanaSankar.

Dr. Mira Maximos (PharmD) completed an Honours Specialization in Health Sciences and Major in Physiology at Western University & Bachelor of Science in Pharmacy at the University of Waterloo. She then completed a hospital pharmacy residency at London Health Sciences Centre concomitantly with a Master of Science in Pharmacy and went on to pursue a Doctor of Pharmacy degree at the University of Waterloo. Dr. Maximos works at Woodstock Hospital in Ontario as the Antimicrobial Stewardship Pharmacy Lead, with @firstlineorg as the Knowledge Mobilization pharmacist, and the Centre of Excellence in Women’s Health as a Research Associate, on contract. She has been involved in research in different areas from medication taking behaviours, to medication safety and knowledge translation. Dr. Maximos lectures at the University of Waterloo in areas such as drug induced disease and infectious diseases in the elderly. Like Dr. Sankar and Dr. Gauthier, she participates in the COVID-19 Resource Canada Q&A town halls as a clinician-scientist. You can follow her on Twitter @miramaximos.

Conflicts of Interest

  • Kimberley Gauthier declares no conflicts of interest
  • Amir Imani declares no conflicts of interest
  • Krishana Sankar declares no conflicts of interest
  • Mira Maximos is employed with Firstline Mobile Health as a Knowledge Mobilization pharmacist

This blog post is for information/educational purposes only, and does not substitute professional medical advice. Also please note that opinions are those of the authors and do not necessarily reflect that of their employers.


References:

1. Alvis-Miranda, Hernando Raphael, Sandra Milena Castellar-Leones, Gabriel Alcala-Cerra, and Luis Rafael Moscote-Salazar. 2013. Cerebral Sinus Venous Thrombosis. Journal of neurosciences in rural practice 4(4): 427–38. .

2. Coutinho JM, Zuurbier SM, Aramideh M, Stam J. The incidence of cerebral venous thrombosis: a cross-sectional study. Stroke. 2012 Dec;43(12):3375-7. doi: 10.1161/STROKEAHA.112.671453. Epub 2012 Sep 20. PMID: 22996960.

3. Ferro José M., Canhão Patrícia, Stam Jan, Bousser Marie-Germaine, and Barinagarrementeria Fernando. (2004). Prognosis of Cerebral Vein and Dural Sinus Thrombosis. Stroke, 35(3), 664–670. https://doi.org/10.1161/01.STR.0000117571.76197.26

4. Costello RA, Nehring SM. Disseminated Intravascular Coagulation. 2020 Jul 17. In: StatPearls. Treasure Island (FL): StatPearls Publishing; 2021 Jan–. PMID: 28722864.

5. Selleng K, Selleng S, Greinacher A. Heparin-induced thrombocytopenia in intensive care patients. Semin Thromb Hemost. 2008 Jul;34(5):425-38. doi: 10.1055/s-0028-1092872. Epub 2008 Oct 27. PMID: 18956282.

6. Warkentin TE, Basciano PA, Knopman J, Bernstein RA. Spontaneous heparin-induced thrombocytopenia syndrome: 2 new cases and a proposal for defining this disorder. Blood. 2014 Jun 5;123(23):3651-4. doi: 10.1182/blood-2014-01-549741. Epub 2014 Mar 27. PMID: 24677540.

7. Greinacher A, Thiele T, Warkentin TE, Weisser K, Kyrle PA, Eichinger S. Thrombotic Thrombocytopenia after ChAdOx1 nCov-19 Vaccination. N Engl J Med. 2021 Apr 9. doi: 10.1056/NEJMoa2104840. Epub ahead of print. PMID: 33835769.

8. Schultz NH, Sørvoll IH, Michelsen AE, Munthe LA, Lund-Johansen F, Ahlen MT, Wiedmann M, Aamodt AH, Skattør TH, Tjønnfjord GE, Holme PA. Thrombosis and Thrombocytopenia after ChAdOx1 nCoV-19 Vaccination. N Engl J Med. 2021 Apr 9. doi: 10.1056/NEJMoa2104882. Epub ahead of print. PMID: 33835768.

Websites and Videos:

1. Centre for Disease Control. 2020. Venous Thromboembolisms (Blood Clots). (March 30, 2021)

2. Health Canada. 2021. AstraZeneca COVID-19 Vaccine and COVISHIELD: Risk of Thrombosis with Thrombocytopenia. (Mar 24, 2021)

3. Health Canada. 2021. AstraZeneca COVID-19 Vaccine Product Monograph. (April, 14, 2021)

4. Health Canada. 2021. Health Canada provides update on the AstraZeneca and COVISHIELD COVID-19 vaccines. (April 14 2021)

5. Macleans (Opinion). Younger and sicker: What Canada’s variant-driven third wave looks like.. (March 30, 2021)

6. Ontario COVID-19 Science Advisory Table. (2021). Vaccine-Induced Prothrombotic Immune Thrombocytopenia (VIPIT) Following AstraZeneca COVID-19 Vaccination. (March 26, 2021)

7. Thrombosis Canada. 2020. Deep Vein Thrombosis (DVT): Diagnosis or Treatment (March 30, 2021)

8. Winston Centre for Risk and Evidence Communication. 2021. News- Communicating the potential benefits and harms of the Astra-Zeneca COVID-19 vaccine. (April 23, 2021)

Timeline

The timeline below summarizes the incredible and rapid global response that went into the identification, assessment, monitoring and recommendations associated with a rare adverse event correlated with the AstraZeneca COVID-19 vaccine. The speed of this response speaks to the remarkable impact of pharmacovigilance and public health initiatives worldwide.

April 23, 2021

NACI updated their recommendation for use of the AstraZeneca vaccine , and now advises Canadians aged 30 and may be offered this vaccine, provided that:

  • Benefits of earlier vaccination with AstraZeneca outweigh risks of developing VITT or risk of contracting COVID while waiting for an mRNA vaccine
  • The individual provides informed consent and understands risks of VITT compared to risk of COVID-19, how long they would have to wait for an mRNA vaccine, and how to minimize risk of COVID-19 exposure
  • The delay in accessing an mRNA vaccine is too long

NACI preferentially recommends mRNA vaccines due to the protection they provide, the lack of safety signals, and the acceptance of these vaccines among the public. NACI bases these current recommendations on a broad view of the evolving epidemic across Canada, and recognizes that the risk-benefit analysis will vary regionally based on community transmission levels, logistics, and vaccine supply.

April 20, 2021

The following provinces lowered minimum age for the AstraZeneca COVID-19 vaccine:

From 55 to 40:

From 55 to 45:

The Society of Obstetricians and Gynecologists of Canada (SOGC) statement

  • Supports administration of any of the four vaccines currently authorized in Canada in people at any stage of pregnancy, and in breastfeeding.
  • Recommends prioritizing pregnant women for COVID vaccination .
  • Notes that COVID-19 presents severe health risks in pregnancy with 1 in 10 pregnant COVID-19 patients hospitalized, and 1 in 100 requiring intensive care.
  • For more information please see the SOGS COVID-19 resources page.

April 17, 2021

The second case of rare thrombosis with thrombocytopenia linked to the AstraZeneca COVID-19 vaccine in Canada.

  • This second case was reported after more than 700,000 doses of AstraZeneca or COVISHIELD were vaccines administered around the country.
  • Dr. Deena Hindshaw, Alberta, Canada’s Chief Medical Officer of Health announced that a rare case of thrombosis with thrombocytopenia linked to the AstraZeneca COVID-19 Vaccine was diagnosed.
  • The patient was promptly treated and is recovering.

April 14, 2021

Health Canada updated the AstraZeneca and COVISHIELD COVID-19 vaccines advisory page based on a thorough and independent assessment of the literature noting a case report of these rare clots occurring post administration of the first dose of the COVIDSHIELD vaccine in Canada. Health Canada concluded that these rare events may be linked to the vaccine, with an incidence rate of 1 in 250,000. Regulators around the world also released a similar (statement/advisory) inline with the World Health Organization (WHO)’s statement released April 7, 2021.

April 13, 2021

The first known case of thrombosis with thrombocytopenia in Canada was reported in Quebec associated with the COVISHIELD vaccine.

April 8, 2021

Australian Technical Advisory Group on Immunization (ATAGI) statement on the AstraZeneca COVID-19 vaccine in response to the safety concern of rare blood clots:

  • Recommendation that the alternate vaccines available (Pfizer’s Comirnaty) be preferred over the AstraZeneca vaccine in adults under 50 years of age.
  • The AstraZeneca vaccine can still be used in adults under 50 years of age if benefits outweigh risk or if an informed decision has been made by an individual.
  • For those who have received their first dose of the COVID-19 AstraZeneca vaccine, a second dose can be given if no serious adverse events were experienced.

April 7, 2021

European Medicines Agency (EMA)’s Pharmacovigilance Risk Assessment Committee (PRAC):

  • Concluded that the very rare cases of thrombosis with thrombocytopenia should be listed as a very rare adverse effect of the AstraZeneca vaccine vaccine (Vaxzevria).
  • The EMA confirms that the overall benefit of vaccination outweighs risk.

World Health Organization’s subcommittee on vaccine safety (GACVS):

  • Provides an interim statement on the AstraZeneca COVID-19 vaccine based on data from health authorities and notes that based on current information, a causal relationship between the vaccine and these rare blood clots is possible but not confirmed.

March 31, 2021

PRAC (Europe) brought together a group of ad hoc experts (hematologists, neurologists and epidemiologists) to discuss:

  • The possible mechanisms underlying the rare cases of the unusual blood clots associated with few people vaccinated with AstraZeneca’s COVID-19 vaccine,
  • Potential identifiable underlying risk factors,
  • Additional data required to further characterize the observed events.

March 29, 2021

During a virtual briefing:

  • Dr. Supriya Sharma (Chief Medical Advisor to the Deputy Minister) and Dr. Howard Njoo (Deputy Chief Public Health Officer) explained that Health Canada will release additional guidelines for use of the AstraZeneca vaccine.
  • Health Canada will be requiring AstraZeneca manufacturers to conduct a detailed assessment of benefits and risks of the vaccine.
  • These analyses, along with international evidence, will be used to guide future regulatory actions.

The National Advisory Committee on Immunization (NACI) :

  • Provided a recommendation that the AstraZeneca COVID-19 vaccine not be used in adults under 55 years of age while the safety signal for a rare clotting adverse event was being investigated.
  • The NACI update cites an Ontario Science Table Science Brief (March 26, 2021) that provides information on a proposed pathogenesis, presentation, work-up and treatment of VITT (also known as VIPIT).

March 26, 2021

Ontario Science Table released a report regarding a proposed mechanism of VITT (VIPIT) for the rare cases of blood clots:

  • Noted in the United Kingdom (UK), European Union and Scandanavian countries (EEA) following AstraZeneca COVID-19 Vaccination.
  • Led by Dr. Menaka Pai MSc MD FRCPC, this report provides a lay summary for the public, as well as information on the pathophysiology, diagnostics, and proposed treatment alternatives of the blood clots associated with the AstraZeneca vaccine.
  • The report describes a possible mechanism identified by the Society of Thrombosis and Haemostasis Research (GTH) in Germany, whose research team suspects that this thrombosis with thrombocytopenia mimics heparin-induced thrombocytopenia.

March 24, 2021

Health Canada provided an update regarding the AstraZeneca COVID-19 vaccine and risk of thrombosis with thrombocytopenia.

  • Neither the AstraZeneca nor COVISHIELD vaccines were associated with increased risk of overall thrombosis.
  • A possible risk of thrombosis with thrombocytopenia was flagged for the AstraZeneca vaccine.
  • Monitoring and guidance will continue.
  • Instructions were provided regarding when to seek immediate medical attention for signs and symptoms of thrombosis.

March 18, 2021

The Pharmacovigilance Risk Assessment Committee (PRAC) of European Medicines Agency (EMA) provided a preliminary report on a signal of rare blood clots in individuals vaccinated with the AstraZeneca COVID-19 vaccine.

  • 20 million people vaccinated in the UK and EEA with the AstraZeneca vaccine as of March 16th 2021.
  • 7 cases of disseminated intravascular coagulation (DIC) and 18 cases of cerebral venous sinus thrombosis (CVST) were noted.
  • To ensure continued pharmacovigilance, the PRAC committee would be monitoring these events to determine correlation and provide updates as details became available.

March 11, 2021

Health Canada shared a statement acknowledging that countries in Europe were noting rare incidences of thromboembolic events following vaccination with the AstraZeneca COVID-19 Vaccine.

  • At that time, Health Canada did not find any indication that the vaccine caused these events according to data that was available and was able to share that no adverse events related to either the AstraZeneca or COVISHIED vaccines were reported in Canada.
  • Initially, there was a question regarding if a specific batch was associated with this adverse outcome but none of these batches under investigation were shipped to Canada. Health Canada initiated an investigation into these thromboembolic events and continued to work with international regulators on gathering further data regarding this adverse event.

Note to our readers Thank you for reading this blog post. We hope it provides a good overview of a snapshot in time about the rare adverse drug reaction (ADR) of thrombosis with thrombocytopenia associated with the AstraZeneca COVID-19 vaccine. New information on this topic will be housed in a future blog resource so as to not create a document that is too large to navigate.

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Timeline References Websites and Videos: