TORONTO - Many Ontarians aged 80 and older became eligible to book their second COVID-19 vaccine doses on Monday, though some regions said a lack of supply meant they couldn't offer second shots to the oldest seniors right away.

The government announced last week that it was shortening the intervals between doses, starting with the 80 and older cohort, but left it up to individuals to schedule earlier shots.

Some said they were able to quickly rebook appointments for their loved ones on Monday morning.

Karthik Kanagas said he was able to move his father's second-dose up to Wednesday - far earlier than the original appointment booked for July at a Toronto clinic.

“He's incredibly relieved,” Kanagas said. “He's looking forward to having a little bit of freedom of mobility again, to go grocery shopping and do those little things.”

Mo Saeed was able to reschedule a second dose for his 80-year-old father-in-law, moving up the shot by six weeks.

“He's excited to be getting it sooner,” said Saeed, adding that he would have preferred if his Mississauga, Ont.-based father-in-law had received an email or call from about rescheduling.

The government has been criticized for not having a plan to contact recipients directly to move up second doses. Residents will keep their original second-dose appointments - four months from the first - if they don't book an earlier shot.

Not all health units were able to start offering earlier second doses to the 80 and older cohort on Monday.

The Middlesex-London Health Unit said vaccine supply challenges meant it would offer earlier second shots to that group starting June 7, though possibly sooner, as it prioritized first shots.

The health unit covering Sudbury, Ont., said second shots for the oldest seniors would likely become available the week of June 28, based on known supply and plans to prioritize youth for first shots.

“I thank everyone for your ongoing patience and understanding,” Dr. Penny Sutcliffe, the region's top doctor, said in a statement.

Lynne Witty said she was disappointed after calling pharmacies and the Sudbury health unit on Monday in an attempt to speed up her 87-year-old mother's second vaccine appointment.

“It's frustrating because she hasn't been able to visit with family, so she's been housebound since this all started,” Witty said.

Thunder Bay's health unit asked people not to show up at clinics without booking first. In Ottawa, technical difficulties thwarted those trying to book shots and the city said Monday morning it was pausing all bookings due to issues with the provincial system.

Those 70 and older will see their dose interval shortened in mid-June, and after that, residents will become eligible for second doses based on when they received their first shot.

The expanded vaccine effort came as Ontario reported 916 cases of COVID-19 on Monday - its lowest daily total since Feb. 17 - and 13 more deaths from the virus. The new cases were based on 18,200 completed tests.

Later Monday, the government was to table a motion that would replace the province's top public health doctor.

Health Minister Christine Elliott said the province is moving to replace Dr. David Williams with Dr. Kieran Moore.

Moore currently serves as the top doctor at the Kingston-area public health unit, and is expected to take over as Ontario's chief medical officer of health on June 26.

Williams had been slated to retire in September, but his last day has been pushed up by several months. Elliott said Moore will start working with Williams on June 7 to ensure a smooth transition.

Elliott said Moore was a “logical choice” out of the province's 34 local medical officers of health due to his success managing the pandemic and relevant experience in his medical career.

Opposition politicians said they were supportive of the change but had questions about what they called a lack of transparency around the process.

“We usually have a committee that sits and discusses the chief medical officer replacements. That didn't happen and we think that we need to be engaged,” NDP Leader Andrea Horwath said.

Also Monday, Ontario announced a policy making it mandatory for staff in long-term care homes to provide proof of COVID-19 vaccination, documentation of a medical reason not to be vaccinated or participate in an educational program about vaccination. Homes will be required to track and report on the progress of their COVID-19 immunization policies.

Meanwhile, Premier Doug Ford continued to mull whether to reopen schools for the last few weeks of the academic year, saying an announcement would come “in the next day or two.” He asked experts, public health officials, teachers' unions and numerous stakeholders for advice on the matter late last week.

- With files from Denise Paglinawan.

This report by The Canadian Press was first published May 31, 2021.