Ontario will be expanding third dose COVID-19 vaccine eligibility in mid-December, allowing individuals aged 50 and up to get the booster shot.

Individuals in this age group will be able to book their appointments starting at 8 a.m. on Dec. 13 through the provincial vaccine portal or call centre, at a pharmacy or at their family doctor's office. Ontarians must wait at least six months after they get their second dose to get the booster.

The province also released further instruction for high-risk immunocompromised individuals, saying that people receiving dialysis are eligible to receive a third dose of the COVID-19 vaccine as of today—as long as it has been 56 days since their second shot. Officials recommend that people who receive hematopoietic stem cell transplants, hematopoietic cell transplants, and recipients of CAR-T-cell therapy be "re-vaccinated" due to "loss of immunity following therapy or transplant."

A limited supply of single dose Johnson & Johnson COVID-19 vaccine will also be available as of Thursday for adults who have had an allergy or cannot get a mRNA vaccine for a medical reason.

It can also be requested by an individual who has not yet been vaccinated through a public health unit, officials say.

“If you are eligible for a booster dose of the COVID-19 vaccine, please book your appointment as soon as you can to provide yourself with an extra layer of protection,” Ontario's Chief Medical Officer of Health Dr. Kieran Moore said. "Achieving the highest vaccination rates possible remains our best tool to protect us, reduce the risk of COVID-19 transmission, and fight the significant surge of new cases and the new Omicron variant.”

As of Thursday, there are five cases of the Omicron variant in Ontario, including one case in Durham Region.

Moore added that while he is still waiting on data regarding the efficacy of vaccination against Omicron, he does believe there will be some evidence of protection.

"Our main enemy right now is Delta. It's 99.9 per cent of the strains that we're identifying in Ontario and we know this vaccine has significant benefits in protecting against hospitalization," he said. "so our strategy really is to maximally protect all Ontarians with first, second and third doses given that Delta is our enemy. I do hope and wish that it gives us also protection against Omicron, but I have to be completely honest that we don't have the science to make that statement yet."

Ontario's current guidelines limits booster shots to certain high-risk populations, including those over the age of 70, residents in long-term care and retirement homes, individuals who received two doses of the AstraZeneca vaccine, people who are immunocompromised, and Indigenous people.

The CEO of Ontario's Pharmacists Association said Thursday morning that he would recommend opening up eligibility to all age groups, while still adhering to the recommended six-month timeline.

"That will allow us to do this in a staggered fashion, manage the demand and supply and make sure everybody has optimal immunity and efficacy of the vaccines against the variants because the immunity does wane after six months. We know that from the current data and that's why boosters are going to be so important."

However, Moore said the province wants to ensure it has the capacity to offer booster shots along with vaccinated children prior to removing all age restrictions.

"I really want the over 70s in particular to come forward as we know they're most at risk of fading immunity and a risk for transmission. In these next 10 days you will be well protected for the holiday season and children will get the maximum benefit of being immunized in the next 10 days for the holiday season as well." Moore said.

"So to me these next 10 days we build capacity to ensure that those populations have the opportunity to get immunized. We then build capacity for the next vulnerable group, the over 60 and over 50s on (Dec. 13)."

As of Monday, the province was sitting on a supply of 3.7 million doses of COVID-19 vaccine.

The government has said that booster shots would be available gradually to the general public based on age and risk factors starting in early 2022.

Officials say that more than 696,000 third doses have been administered in Ontario so far.