TORONTO -- Health officials in Ontario are reporting a third case of a rare blood clot associated with AstraZeneca’s COVID-19 vaccine.

Ontario’s Chief Medical Officer of Health Dr. David Williams said Monday that a man in his 70s is the latest person to suffer a clot after receiving a dose of the vaccine. The man is now receiving treatment in hospital.

The province reported its first two cases last week of the condition, known as vaccine-induced immune thrombotic thrombocytopenia (VITT).

One of them was in a man in his 60s who was recovering at home after receiving treatment. The family of the other person – a Hamilton man in his 60s – told CTV News that he is now fighting for his life in hospital after suffering a severe stroke associated with the clot.

Ontario has now given out around 650,000 doses of the AstraZeneca vaccine, and Williams said the chances of an extreme adverse reaction remain low.

“So we are continuing to monitor the situation, we are continuing to document these, to investigate them, and in partnership with our federal, provincial, territorial teams, we're looking at those on a national basis,” Williams said at a news conference Monday.

He noted that while there is a small risk associated with the AstraZeneca vaccine, it is very small "compared to other similar medications and very low compared to getting COVID and the complications of COVID.”

“So we still want to encourage everyone, when is your turn or opportunity to get a vaccine, to obtain the vaccine,” Williams said.

He added that the province is already starting to see the benefits of vaccination among its older population, who have been at the front of the line for doses.

“We're seeing many strong indications of the benefit of immunization, as our case rates in the older population groups — those over 60, definitely those over 80 — and our death rates have come down, as well as our hospitalization rates in those age groups are coming down,” Williams said. “So it shows you that the vaccine is working.”

Last week, the province lowered the age threshold to 40 for those who want to obtain an AstraZeneca dose through a pharmacy or doctors’ office. The National Advisory Committee on Immunizations (NACI) also lowered its own recommendation to those 30 and over, but Ontario said it would not reduce the age restriction further until there is more supply available.

Some 4.1 million doses of the vaccine are expected to arrive in Canada through various sources by the end of June. There are also reports that the United States might allow some of its stockpile to leave the country soon. The U.S. is believed to have tens of millions of AstraZeneca doses either stored or in various stages of production as part of a contract with the company, but has refused to let most of those doses leave the country so far.