The Ontario government will announce on Thursday that it will lower the age of eligibility for COVID-19 booster shots to people aged 50 and older this year, sources say.
Two sources told CBC Toronto that the expansion of eligibility is expected to begin around mid-December. The news was first reported by the Globe and Mail.
Dr. Kieran Moore, Ontario's chief medical officer of health, is scheduled to detail the plan at a news conference Thursday afternoon.
Those presently eligible for a booster in Ontario are people aged 70 and older, health-care workers or essential caregivers in congregate settings, people who received two doses of the AstraZeneca vaccine or one dose of Janssen, and First Nations, Inuit and Métis adults and their non-Indigenous household members.
Moore said on Monday that the province is reviewing its third-dose vaccine strategy in the wake of the discovery of the new omicron variant. That strategy might be accelerated, he said.
"We will be reviewing options and providing them to government in the next few days, and I would anticipate an announcement by the end of this week on an enhanced strategy to best protect Ontarians," he said.
A booster shot is meant to improve the immune response of a regular two-dose vaccine regimen which, with time, can "[fall] below a rate deemed sufficient," according to the World Health Organization.
Dr. Zain Chagla, an infectious diseases physician at St. Joseph's Healthcare Hamilton and an associate professor at McMaster University, questioned how low the eligibility age should be.
Chagla said data shows that the vast majority of "breakthrough cases" that require hospitalization are in people over 60, while the hospitalization rate among people who get COVID-19 after two doses in the 50 to 60 age group is about one or two per cent.
"Going down a little bit will capture some of those breakthrough cases and may provide some extra immunity for some of our vulnerable populations. It may reduce some transmission among those groups. But the health-care demand right now is not being faced by people that are getting or needing their third doses. The health-care demand right now in Ontario is because of people that have not taken their first doses," Chagla said.
As for the presence of omicron, he said not enough is known about the variant to determine what kind of difference two or three doses will make.