Based on the latest recommendations of the National Advisory Committee of Immunizations (NACI), Ontario is halting the use of the AstraZeneca vaccine for people under 55.  

At a news conference on Monday, the province’s Chief Medical Officer of Health Dr. David Williams said Ontario will follow NACI’s recommendations while it waits for more information on the vaccine. 

“Rare cases of serious blood clots, including cerebral venous sinus thrombosis, associated with thrombocytopenia have been recently reported in Europe following post-licensure use of AstraZeneca COVID-19 vaccine,” NACI said in statement posted on the Government of Canada website. “Cases identified so far have been primarily in women under the age of 55 years; although cases in men have also been reported and have mostly occurred between 4 and 16 days after receipt of the vaccine.” 

This adverse event is being referred to as Vaccine-Induced Prothrombotic Immune Thrombocytopenia (VIPIT). The exact mechanism by which the AstraZeneca vaccine triggers VIPIT is “still under investigation”  but at this time “no other risk factors have consistently been identified in patients who develop VIPIT”, the statement added.

The statement also noted that this adverse event has not been identified following receipt of mRNA COVID-19 vaccines to date.

Dr. Williams said that the province is consulting with health officials in the United Kingdom, where the vaccine has been used extensively, to understand the risks.

While the AstraZeneca shot has not been widely used in people under the age of 55 here, Canada is expected to receive 1.5 million doses of this product from the United States which has not yet approved its use in the American marketplace.

Adults 55 years of age and older may still be offered the AstraZeneca vaccine with informed consent, given the increased risk of hospitalization and death due to COVID-19 disease in this population and since VIPIT appears to be  a rarer event in that age group, NACI says. However, anyone receiving the AstraZeneca COVID-19 vaccine should be informed of this potential adverse event and advised to seek immediate medical attention if they develop symptoms between days 4 and 20 following receipt of the AstraZeneca vaccine.

Symptoms to be vigilant for include: shortness of breath, chest pain, leg swelling, persistent abdominal pain, neurological symptoms including sudden onset of severe or persistent worsening headaches or blurred vision, skin bruising (other than at the site of vaccination) or petechiae.

“Canada is expected to receive sufficient mRNA COVID-19 vaccines to fully vaccinate the population with two doses of mRNA vaccine before fall 2021. The AstraZeneca COVID-19 vaccine was expected to make up a small proportion of the COVID-19 vaccines available for use in Canada; therefore, COVID-19 vaccinations will not be significantly delayed without using it in younger adults,” the government said.

 

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