The provincial government says it can now offer medical workers dealing with COVID-19 patients, COVID-19 testing centre staff and first responders a second vaccine dose at a shorter interval than the general public due to increasing supply.

Starting later this week, all hospital staff dealing with COVID-19 patients or at high risk of infection, COVID-19 specimen collection and lab testing personnel, first responders, community health workers and essential caregivers of long-term care residents will be able to book second dose vaccine appointments.

Starting in March, the province adopted federal guidance that pushed second doses out up to 16 weeks from the first, instead of the 21 to 28 days recommended by vaccine manufacturers, in a bid to maximize protection offered by the jabs in the context of constrained supply.

"The good news is that we're receiving much larger quantities of vaccines, particularly the Pfizer vaccines, and so we will as soon as we're able to expand those categories as well," Health Minister Christine Elliott told reporters at Queen's Park on Monday.

She added that they may expedite second shot appointments for other groups in the near future.

"We have expanded for three categories (today). Now we are looking at older adults in addition to that group."

The end result involved some medical workers in COVID wards working all day alongside infected persons with the protection of just one dose, which does not guarantee immunity from infection.

Home care workers, those who work needle exchanges and some general practitioners in remote communities will also be eligible to move up their second shot appointments.

The move comes as the province moves to expand eligibility for COVID-19 vaccination more generally, with an aim to offer a first dose to 65 per cent of the province’s adult population by the end of the month.

On Tuesday at 8 a.m., most cancer patients, dementia and diabetes sufferers can begin booking vaccine appointments on the provincial portal.

On Thursday at 8 a.m., all those 40 and older, regardless of residence can begin registering for a COVID-19 vaccine appointment on the provincial portal.

Ontario is set to receive at least 800,000 doses of coronavirus vaccine this week.