Canada's National Advisory Committee on Immunization (NACI) has recommended that the AstraZeneca Covid-19 vaccine should not be used in adults under 55 years of age at this time, while rare cases of serious blood clots were being further probed.

In a statement issued on Monday, the NACI said the cases, known as vaccine-induced prothrombotic immune thrombocytopenia (VIPIT), "have been recently reported in Europe following post-licensure use of the AstraZeneca Covid-19 vaccine".

"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 four and 16 days after receipt of vaccine."

The statement further said: "Following population-based analyses of VIPIT assessing risk of Covid-19 disease by age, and considering that alternate products are available (i.e., mRNA vaccines), from what is known at this time, there is substantial uncertainty about the benefit of providing AstraZeneca Covid-19 vaccine to adults under 55 years of age given that the potential risks associated with VIPIT, particularly at the lower estimated rates.

"As a precautionary measure, while Health Canada carries out an updated benefit/risk analysis based on emerging data, NACI recommends that the vaccine not be offered to adults under the age of 55.

"Adults 55 years of age and older may still be offered the AstraZeneca vaccine with informed consent, given the increased risk of hospitalisation and death due to Covid-19 in this population and since VIPIT appears to be a rarer event in that age group."

According to the Committee, the "rate of this adverse event is still to be confirmed" and information is being gathered to be more accurate.

"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 of thromboembolism and/or thrombocytopenia between days four and 20," it added.

Canada's move comes after over a dozen European countries had halted their use of the vaccine due to the blood clot issue.

Some nations have resumed vaccinations while others have continued their suspensions.

Canada has so far reported 976,327 coronavirus cases and 22,871 deaths.