KITCHENER -- People aged 55 and older will be able to pre-register for a COVID-19 vaccine starting Saturday in Waterloo Region.

Pre-registration will also open to people with certain at-risk health conditions, including diabetes, heart disease and liver disease.

"Anyone who has already pre-registered, who is waiting for a booking invitation, will be contacted within four to six weeks, as vaccine becomes available," Dept. Chief Shirley Hilton said at the region's COVID-19 briefing on Friday. "I would also like to reassure everyone that you will be invited to book an appointment in the order you're invited to register."

Hilton said vaccine supply is still unstable in the region, particularly with doses of AstraZeneca and Moderna. Pfizer supply is expected to increase into the end of May. She added that clinics may need to temporarily close while officials wait for more supply.

On Thursday, Ontario released a tentative timeline for booking vaccines through the provincial system, with a goal of opening appointments to everyone over the age of 18 by the end of May. Waterloo Region uses its own booking system.

Hilton said the local vaccine task force is evaluating local supply and will provide an update soon on whether or not the region will be able to follow that schedule.

Regional officials reported that they will surpass 200,000 vaccine dosesadministered on Friday.

CASE COUNTS STABILIZING UNDER STAY-AT-HOME ORDER

Medical Officer of Health Dr. Hsiu-Li Wang said the region is starting to see the impact of the stay-at-home order. However, as things stabilize, she said the situation remains precarious both locally and across Ontario.

"It will change quickly if we don't keep up with our public health measures," she said.

Waterloo Region's weekly incidence rate sits at 95 cases per 100,000 people per week.

Dr. Wang continued to encourage residents to stay home as much as possible and limit close contacts.

She also recommended sending one person from each household for essential trips, and planning in advance to keep trips as short as possible.

"Residents are illustrating their care and support for each other," Dr. Wang said. "By following the stay-at-home order and practicing the public health precautions, your efforts are starting to have an impact."

Although case counts have stabilized, Dr. Wang said hospitalizations and deaths are still rising. The region is also accepting patients from other regions.

"Waterloo Region accepting cases from outside of our region is basically saving lives," Dr. Wang said.

Dr. Wang added the hospital system across Ontario needs to operate as one system to ensure equitable health-care for people in the province.

"If we reopen too quickly, if cases go back up again and our health system is overwhelmed, we're just going to be under restrictions for longer and it's going to hurt more," she said.

She said people need to stay the course for now to help drive down case numbers, hospitalizations and deaths.