TORONTO -- York Region residents aged 35 and older in five priority postal codes will now eligible to book an appointment to receive their first dose of a COVID-19 vaccine at city-run mass vaccination sites, officials confirmed on Monday.

The priority postal codes are L4L, L6A, L4K, L4J, which are located in Vaughan, and L3S, a Markham postal code.

All residents of York Region who are 60 and older are also eligible to receive a shot.

Patrick Casey, the director of corporate communications for York Region, said approximately 20,000 new vaccine appointments will open up tomorrow morning at 8:30 a.m.

“York Region continues experiencing a serious reduction in vaccine supply and will offer additional appointments as vaccine becomes available,” Casey said in an email to CP24.

The provincial government has confirmed that effective Tuesday, it will be lowering the age of eligibility for the AstraZeneca vaccine to every resident of the province who is 40 and older.

Although the vaccine is licensed for use for those 18 and older in Canada, the current recommendation from the federal government’s immunization advisory committee is that the vaccine only be offered to people 55 and older due to an extremely rare risk of a significant blood clot. On Sunday, federal Health Minister Patty Hajdu said the National Advisory Committee on Immunization is now reviewing their advice on AstraZeneca.

The AstraZeneca vaccine is being distributed across the province through pharmacies and primary care providers.

“York Region residents age 40 years of age and older are encouraged to book vaccine appointments at select pharmacies and primary care settings in York Region or at the Soccer City vaccine clinic in Whitchurch-Stouffville,” Casey said.