OTTAWA -- Canadians whose first dose of a COVID-19 vaccine came from Oxford-AstraZeneca can safely be offered a second dose of either Pfizer-BioNTech or Moderna, the National Advisory Committee on Immunization said Tuesday.

The news should ease the fears of some Canadians who got the AstraZeneca shot before much was known about its potential link to a rare but serious new blood clotting syndrome.

It comes as chief public health officer Dr. Theresa Tam reported Canada's COVID-19 infections are down 70 per cent from the third-wave peak in mid-April, and 20 per cent from just last week.

Hospitalizations are down 40 per cent, and ICU admissions and deaths are both down 25 per cent, compared to mid-April, she said.

Tam said Canadians have "stepped up to do their part at every turn" of this pandemic and the hard work is paying off.

That included, she said, getting vaccinated, with more than 21.9 million people now at least partly vaccinated against COVID-19, including 2.1 million fully vaccinated.

Canada is moving more quickly to get second doses into arms -- about one in five new shots in the last three days were second doses, compared to fewer than one in 10 in most of May.

"Public health authorities are now compressing that second dose now that vaccines are more available," Tam said. "They will not be going to 16 weeks."

She noted however that real-world data has shown waiting eight to 12 weeks to give a second dose is producing a stronger immune response than going with the three to four weeks that were used in the initial clinical trials.

With vaccine supplies now more plentiful, most provinces have moved in the last week to cut the second-dose wait from 16 weeks down to eight to 12 weeks.

All provinces had halted the use of AstraZeneca for first doses, and some weren't even using it for second doses pending the NACI guidance that came today.

The committee's advice is based on interim results from studies in the United Kingdom and Spain showing mixing and matching COVID-19 vaccines is safe, and in the Spanish study, effective. Further results from those studies are expected this month.

NACI also said vaccines from different manufacturers for other illnesses are routinely mixed as long as they show similar effectiveness, target the same populations, and use similar antigens, a molecule on the outside of a virus that makes it unique.

Tam said the NACI decision is entirely driven by the risk of vaccine-induced thrombotic thrombocytopenia.

"If it wasn't for that, then probably one would progress with giving the same dose as the second dose," she said.

Canada joins Denmark, Finland, France, Germany, Sweden, Norway and Spain among countries mixing and matching vaccines because of the risk of VITT.

Alberta, Saskatchewan, Nova Scotia and Prince Edward Island moved immediately to begin offering AstraZeneca recipients a second dose of an mRNA vaccine if they wish, joining Manitoba which did so Monday, and Quebec, which began allowing it last week.

"While AstraZeneca is still a good choice, we will offer Albertans a choice," said Alberta Health Minister Tyler Shandro Tuesday afternoon.

Quebec still recommends people get the same vaccine for their second dose and noted the risk of VITT is about one in 60,000 people for the first dose, but about one in 600,000 after the second.

NACI's guidance did not stipulate a preference for which vaccine AstraZeneca recipients should get second.

NACI says for people who got Pfizer or Moderna first, the second dose should be the same unless supply issues prevent that.

AstraZeneca Canada issued a written statement responding to the advice, saying they will continue to work to understand the reports of rare blood clots, but that the vaccine is safe and effective against COVID-19. It has been authorized in more than 80 countries.

"We fully respect the recommendations outlined today by NACI in their advisory role for the use of COVID-19 vaccines in Canada," the statement says.

Forty-one Canadians have now had a confirmed or suspected case of VITT and five have died, out of almost 2.2 million people who received the vaccine to date.

More than 1.5 million Canadians got AstraZeneca as a first dose before NACI advised on April 23 that AstraZeneca doses should only be given to people over the age of 30, who were at high risk of contracting COVID-19, or of getting seriously ill from it.

Ontario and Quebec both reported their lowest daily case totals since the fall Tuesday -- 699 in Ontario, the lowest since mid-October, and 208 in Quebec, the lowest since September.

Quebec Premier Francois Legault -- still basking in the Montreal Canadiens NHL playoff series victory over the Toronto Maple Leafs Monday night -- was all smiles as he told Montreal residents they will be able to dine at a restaurant next week for the first time since Oct. 1.

"Things are going very well everywhere in Quebec," Legault said in French.

Alberta Premier Jason Kenney said his province had just 209 new cases Tuesday, down from more than 2,000 a day a month ago, and thanked Albertans for getting vaccinated and helping to "crush the spike" in COVID-19 cases.

"This is where we start to live the promise these vaccines have brought," said Kenney.

Ontario is still mired in heated arguments about whether schools can reopen for the final weeks of the school year with cabinet discussing the issue Tuesday. Ontario schools have been closed since mid-April.

The province's stay-at-home order expires Wednesday, but it doesn't change much, with non-essential retail still limited to curbside service only, and all restaurants restricted to takeout, currently until June 14.

This report by The Canadian Press was first published June 1, 2021.