The expansion of coronavirus vaccine eligibility to younger age groups is expected to slow down as Manitoba moves to make doses available to police, firefighters and people living and working in certain high-risk communities.

"We have a limited supply of vaccines and so anytime we add new groups, we know that that does use some of that supply," said Dr. Joss Reimer, medical lead of the vaccine task force, during an online conference call with reporters Friday morning.

"Our intent is to focus in on where we see that high, high risk of transmission happening, particularly with the third wave, which does mean that our age decrease will be slower."

The province is in the process of determining which specific geographic areas and which frontline workers in those areas will be eligible. Those details will be announced next Wednesday.

Once the age eligibility reaches younger cohorts, however, the expansion will speed up again, because many people in those groups will already be vaccinated, Reimer said.

A team of doctors, nurses and epidemiologists is working to determine which geographic areas and groups of workers to prioritize, as well as whether more people should be eligible to receive the AstraZeneca-Oxford vaccine.

While that work is happening, the province will not slow down its vaccine rollout to groups that are already eligible, Reimer said.

The province on Friday lowered the age of eligibility to 57 and older for all Manitobans and 37 and older for First Nations people.

"And so doses will continue to go to First Nations communities, if we're talking about Moderna. We'll continue to do some of our pop-up clinics with Moderna. We will continue to use Pfizer at the supersites, while we finalize the plan for this," she said.

At a news conference Friday, Winnipeg Mayor Brian Bowman said he was pleased to see the province adopting a risk-based approach to vaccine eligibility, rather than one based primarily on age.

"I was especially relieved to learn that first responders such as police officers and firefighters will be prioritized for vaccines," Bowman said.

"I've been advocating for this since last year and I'm pleased to see the province finally make a needed change."

The province released a list of more than two dozen communities, including Winnipeg, where pop-up clinics will open from April 18 to 28.

Reimer's latest update was made the day after the province sent out news it will shift vaccine priority to adults living in high-risk communities and people working in public-facing roles in those places, whether or not they live in the communities where they work.

That change will open vaccine eligibility to all police officers and firefighters across Manitoba.

When asked Friday why all firefighters and police officers in Manitoba will be eligible, while for other front-line workers it will be limited to those working in high-risk areas, Reimer said the province is following the guidance of the National Advisory Committee on Immunization, which specifically identified first responders as a priority.

Officials plan to announce next Wednesday exactly which communities and which front-line jobs will be eligible for prioritized vaccination.

Manitoba has so far used age as the primary eligibility requirement for vaccination, because older people are more at risk of getting seriously ill or dying from COVID-19.

Since older adults are now eligible for immunization, it's feasible for Manitoba to start vaccinating younger essential workers, Reimer said on Wednesday.

The operational lead on the vaccine task force, Johanu Botha, said Wednesday that the province will reduce its emphasis on small pop-up clinics in remote and rural communities, in order to shift focus toward large temporary sites in urban areas experiencing high transmission rates. These sites will be stocked with Moderna doses that would have been used in pop-up clinics and by mobile imunization teams.

However, Moderna announced Friday it was slashing planned shipments to Canada this month nearly in half, from 1.2 million doses to 650,000, as the company grapples with production issues at its facilities in Europe.

Reimer said the task force would meet with federal officials Friday morning to discuss the impact the reduced shipments will have on Manitoba, but so far there has been no indication that the timelines for making vaccines available to all adults in the province would have to be extended.