Ontario is reporting its first two cases of a rare blood clot connected to the AstraZeneca vaccine.

In a news release issued Friday morning, Ontario’s Chief Medical Officer of Health Dr. David Williams said the clot occurred in a man in his 60s who had received his first dose of the AstraZeneca/COVISHIELD vaccine.

“The health and safety of Ontarians remains our top priority,” Williams said in the statement. “While these serious reactions remain extremely rare, we have a robust process in place to monitor for any adverse events and have taken steps to ensure that these events are identified and treated as quickly as possible.”

The man has received treatment and is recovering at home now.

Williams noted that all COVID-19 vaccines available in the province have been determined to be safe and effective by Health Canada, and have been shown to prevent serious illness, hospitalization and death.

The rare condition, known as vaccine-induced immune thrombotic thrombocytopenia (VITT), has been reported in a handful of cases. There have been around 168 cases in the U.K., where some 21.2 million doses have been administered, or around 7.9 clots per million doses, according to figures released by Britain’s medicine regulator Thursday.

“This case marks the fourth case of VITT out of more than 1.1 million doses of the AstraZeneca/COVISHIELD vaccine that have been administered in Canada to date,” Williams said. “We will continue to actively monitor the evolving situation and safety of all COVID-19 vaccines with our partners across the country.”

On Friday evening, Hamilton Public Health confirmed to CTV News that a male in his 60s who received his first dose of the AstraZeneca vaccine developed the blood clot condition.

"The patient has received treatment and continues to receive care in hospital. Additional details will not be publicly released to protect the patient's privacy," said Dr. Elizabeth Richardson, Hamilton's medical officer of health.

"While these serious reactions remain extremely rare, there is a robust process in place to monitor for any adverse events and have taken steps to ensure that these events are identified and treated as quickly as possible."

The son of the Hamilton man told CTV News Toronto Friday evening that his father has been in hospital since April 18 and is in critical condition.

"The diagnosis was a severe stroke due to a blood clot in the brain," he said. He did not want to be identified to protect his family's privacy.

His father received the shot earlier this month. He said his father started to get confused two weeks later.

"At about 3 a.m., my mother heard a crash. My father had got up to get a glass of water and end up facedown unconscious on the living room floor."

He said his father would need treatment in the intensive care unit for the "foreseeable future."

"Ultimately, my father is going to need care for the rest of his life if he ever comes out of hospital," he said.

"It's one in a million that this would happen to our family."

The vaccine is approved for use in those 18 and older in Canada but its use has been limited in younger people as health officials study the evidence around the rare clotting side effect.

The National Advisory Committee on Immunizations (NACI) had recommended that the use of AstraZeneca be restricted to those 55 and older, as the clots had mainly occurred in younger people, most of them women.

The committee said Friday it is now recommending the vaccine for anyone 30 and over in Canada who doesn’t want to wait for an mRNA vaccine.

Ontario lowered the age restriction for AstraZeneca to 40 this week in an effort to help move through unused doses of the vaccine and to get shots in arms more quickly. However provincial officials said Friday that they would not immediately lower the age threshold because they don’t yet have enough supply.

The province has seen a major leap in its daily vaccination numbers since the change took effect this week, going from fewer than 100,000 daily doses on Monday to roughly 130,000 daily doses for the past three days.

On Wednesday, Dr. Isaac Bogoch who sits on Ontario’s COVID-19 Vaccine Distribution Task Force, said the doses “were flying off shelves” as those 40 and over flocked to pharmacies offering the vaccine.

Bogoch told CP24 that while the chance of clotting is ”not a zero per cent risk,” it is extremely low for most people and said it makes sense to offer the vaccine to a wider range of people based on informed consent.

Health officials have pointed out that not getting a vaccine also carries risks and that COVID-19 itself has been shown to lead blood clots in patients.

Everyday activities such as air travel and use of birth control pose higher blood clot risks and public health officials have urged people to examine the vaccine risks in context.

“Ontario will continue to offer the AstraZeneca vaccine to individuals aged 40 years and over at the time of vaccination or any time in 2021. This approach is helping to maximize the number of people protected as quickly as possible to prevent further transmission and the much higher risks that come from COVID-19 infection,” Williams said.

“The Health Canada approved vaccines are the best way to protect your health and those around you. Ontarians are encouraged to get vaccinated as soon as they are eligible and monitor their health after receiving their vaccination."

Premier Doug Ford, Health Minister Christine Elliott, Mayor John Tory and other eligible public officials have gotten the AstraZeneca dose as a show of confidence in the vaccine.

- with files from Sean Davidson