On March 29, 2021, Canada’s National Advisory Committee on Immunization (NACI) issued a precautionary recommendation that AstraZeneca (COVISHIELD) COVID-19 vaccines temporarily not be offered to those less than 55 years of age in Canada.

This is in response to ongoing investigation in Europe of rare cases of blood clots associated with a syndrome called “vaccine-induced prothrombotic immune thrombocytopenia”, reported among recipients of AstraZeneca COVID-19 vaccine, 4-20 days post-vaccination. The clinical syndrome features venous thrombosis, including unusual sites such as cerebral venous sinus thrombosis, mesenteric vein thrombosis, as well as arterial thrombosis, in association with thrombocytopenia. The cause of these events remains unclear.

The clinical syndrome is rare - estimated at 1:100,000 – 1 million, affecting mainly female vaccine recipients under 55 years age. By comparison, people who have COVID-19 are at high risk of developing blood clots, which occur in about 1 in 20 people who are hospitalized with COVID-19 and in about 1 in 100 people who have COVID-19 but are not hospitalized.

There have been no reports of this reaction in Canada after 300,000 AstraZeneca vaccinations to-date, or in association with either Pfizer-BioNTech or Moderna mRNA COVID-19 vaccines. Health Canada has updated the AstraZeneca (COVISHIELD) COVID-19 product monographs with information about these events at: https://covid-vaccine.canada.ca/info/pdf/astrazeneca-covid-19-vaccine-pm-en.pdf.

NACI continues to recommend use of AstraZeneca (COVISHIELD) COVID-19 vaccine in persons 55 years of age and older, in whom these events have been even more rare. Please inform and reassure eligible persons that these adverse events are very rare, and that the benefits of vaccination far outweigh the risk of COVID-19 disease particularly among older adults. Protection via immunization is the most effective prevention – against not only COVID-19 disease – but also its many potential complications – including blood clots.

Based on current evidence, there is no cause for concern among people who received a dose of the AstraZeneca (COVISHIELD) vaccine greater than 20 days ago.

Please be alert to the signs and symptoms of thromboembolism and or thrombocytopenia particularly among people recently vaccinated. Those vaccinated should be instructed to seek immediate medical attention if they develop symptoms such as shortness of breath, chest pain, leg swelling, or persistent abdominal pain following vaccination. Additionally, anyone with neurological symptoms including severe or persistent headaches or blurred vision after vaccination, or who experiences petechial skin bruising beyond the site of vaccination after a few days, should seek prompt medical attention.

We will keep you apprised of further related updates as more evidence becomes available.

Download the MHO update.

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