The figures for clots or "thromboembolic events" run up to April 14, by when 21.2 million people had received first doses of the vaccine, according to the Medicines and Healthcare products Regulatory Agency (MHRA).
Dr. Williams said a man in his 60s, who received his first dose was treated for vaccine-induced immune thrombotic thrombocytopenia (VITT), and is now recovering at home.
The province's Chief Medical Officer of Health, Dr. David Williams, provided details in a news release, issued on Friday morning.
The committee initially recommended a pause on using AstraZeneca shots for people younger than 55 out of an abundance of caution after reports of rare blood clots.
Ontario will continue offering the vaccine to people aged 40 and older.
Ontario Health Minister Christine Elliott's office said Friday that the province will continue to administer AstraZeneca COVID-19 vaccine to those 40 years of age and older, despite an updated recommendation from Canada's National Advisory Committee on Immunizations (NACI) that it now be offered to those 30 and over.
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Dr. Williams went on to say serious reactions remain extremely rare, and they have a robust process in place to monitor for any adverse reactions to the vaccine.
The advisory body issued its latest guidance on Friday after reviewing new provincial data on the level of risk now posed in Canada by COVID-19.
"On the basis of this ongoing review, the advice remains that the benefits of the vaccine outweigh the risks in the majority of people", the MHRA said on Thursday, reiterating its advice for the shot.
"The Health Canada approved vaccines are the best way to protect your health and those around you".
The federal government has said that 4.1 million more doses of the vaccine are expected to arrive in the country by the end of June, but a delivery schedule to the provinces has not yet been published. "Ontarians are encouraged to get vaccinated as soon as they are eligible and monitor their health after receiving their vaccination".