KITCHENER -- Anyone living in Waterloo Region who received a first mRNA dose on or before May 30 will be able to book an accelerated second dose appointment starting next week, the province announced Thursday.

Accelerated second dose appointments will open on June 23 in Delta hot spot regions. That includes Waterloo Region, Wellington-Dufferin-Guelph, Halton, Peel, Toronto, and York, along with Hamilton, Simcoe, Muskoka and Durham.

Provincial officials also said there are plans to bring pop-up vaccination clinics to high-priority neighbourhoods in Waterloo Region. The clinics will likely accept both walk-ins and appointments, and will offer both first and second doses to eligible residents.

Earlier this week, accelerated second dose appointments were made available to Waterloo Region residents who received an mRNA vaccine on or before May 9. Anyone who falls into that timeframe can fill out a form on the region's website to ask for an earlier second dose appointment.

Over the weekend, the province also shortened the interval following a first AstraZeneca dose to eight weeks.

The National Advisory Committee on Immunization (NACI) released new recommendations for people who received a first dose of AstraZeneca on Thursday. NACI now says a second dose of Pfizer or Moderna is the preferred option. This is due to studies showing an mRNA vaccine for a second dose is more effective than AstraZeneca, and Canada has seen an increased supply of Pfizer and Moderna over the past few weeks.

Dr. Sharon Bal, who is working on the region's vaccine distribution task force, said getting AstraZeneca for one or both doses was still the right choice.

"I think the message should be, if you got two doses of AstraZeneca, that's excellent. You have good protection against illness and very good protection against serious illness and death," Dr. Bal said. "It really isn't a critique of AstraZeneca, as opposed to more evidence of the safety and the power of the mixed dosing schedule and, in particular, covering variants."

Bal added the recommendation doesn't mean you can't get a second dose of AstraZeneca or that you shouldn't. She suggests speaking to your doctor or pharmacist about what option is right for you.

COVID-19 cases and hospitalizations have spiked in Waterloo Region in recent days. On Wednesday, the region reported the most new cases of any health unit in Ontario. Officials said there are concerns about the Delta variant, which was first identified in India, spreading within the community.

Speaking at a press conference on Thursday morning, Premier Doug Ford said he's been in contact with local officials.

"It's all hands on deck there," he said.

At a Board of Health meeting on Wednesday night, Medical Officer of Health Dr. Hsiu-Li Wang said the majority of Delta variant cases in the region are in unvaccinated individuals. At a large, active outbreak at a congregate setting, 87.5 per cent of cases are among unvaccinated individuals and 9.7 per cent are partially vaccinated. Only 2.8 per cent of cases are in fully vaccinated individuals, and Dr. Wang said they weren't fully protected at the time of infection.

Ford said people who aren't vaccinated could put everyone in jeopardy.

"I've always said from day one, I wouldn't force vaccinations on anyone," he said. "But, I've been encouraging everyone, every step fo the way, 100 per cent, get vaccinated because now, it affects the whole K-W area."

"Vaccines work, they are safe and effective, they will help end the pandemic," Minister of Health Christine Elliott said at a press conference Thursday. "The best vaccine for your second dose is the vaccine that is available first."

Elliott, along with Solicitor General Sylvia Jones, urged all Ontarians to book a second dose appointment as early as possible, adding the Delta variant remains a threat in the province.

Jones also added that mixing and matching vaccines is safe and effective, and will help to allow for an expedited rollout of second doses.

"We continue to make strides to speed up vaccines and get more people fully immunized earlier than originally targeted," she said.

Elliott also said the province will provide public health guidance for fully vaccinated Ontarians "shortly."