From Ontario Media Release
"Starting on Monday, December 13, 2021 at 8:00 a.m., individuals aged 50 and over will be eligible to schedule their booster dose appointment through the
COVID-19 vaccination portal, by calling the Provincial Vaccine Contact Centre, through Indigenous-led vaccination clinics,
select pharmacies and primary care settings.
Appointments will be booked for approximately six months (168 days) after a second dose. "
Went and bumped mine up to this Saturday.