Ontario will no longer offer first doses of the AstraZeneca COVID-19 vaccine after an increase in reports of blood clots associated with the shot.

Ontario’s Chief Medical Officer of Health, Dr. David Williams, made the announcement Tuesday afternoon. The vaccine was being offered to anyone over the age of 40 at pharmacies across Ontario.

“It is not that the risk for individuals has gone up extensively at this time, but because it is sometimes severe, we want to be cautious and say ‘let's pause it’ while we look at the data and information,” said Williams.

The UK Medicines and Healthcare products Regulatory Agency has listed the risk of getting a blood clot from the AstraZeneca vaccine at roughly 4 in 1 million or 1 in 250,000.

Chief Health Protection and Emergency Preparedness Officer, Dr. Jessica Hopkins, says 8 Ontario residents have developed blood clots related to the vaccine, representing a 1 in 60,000 risk of thrombotic thrombocytopenia (VITT) reported in the province.

As it stands, the remaining supply of AstraZeneca in Ontario will be reserved for residents who have already received their first dose of the vaccine and are waiting for the second dose. Ontario notes it’s unclear if the vaccine can be mixed with the second dose of another vaccine.

“We maintain that those who received their first dose with the AstraZeneca vaccine did absolutely the right thing to prevent illness, and to protect their families, loved ones, and communities,” adds Williams.

Public health staff and the federal government are tracking any Adverse Events Following Immunization, unwanted side effects that may or may not be caused by a COVID-19 vaccine known as AEFI’s, that have been reported locally and in Canada, respectively.

Out of the 13.4 million estimated doses administered across Canada as of May 11, there have been 4,548 total reports or about 0.034 percent of all doses administered. 3,800 of those reports were considered non-serious, and 768 were considered serious, or 0.006 percent.

If you do develop unexpected symptoms or side effects after receiving the COVID-19 vaccine, you’re asked to contact your local healthcare provider, who will, in turn, report the AEFI to the province and federal governments, which is standard for all vaccines.