OTTAWA -- The National Advisory Committee on Immunization (NACI) is now recommending that people who received a first dose of the Oxford-AstraZeneca vaccine receive a second dose of an mRNA vaccine, such as Pfizer-BioNTech or Moderna.

NACI’s latest advice takes into consideration the most recent evidence on the rare instances of blood clots associated with the AstraZeneca shot and the increase of mRNA vaccine supply arriving on Canadian soil.

It also says it reviewed emerging evidence “suggesting better immune responses” when an individual receives a first dose of AstraZeneca and a second dose of an mRNA vaccine.

“There are just increasing numbers of studies, mostly from Germany, that we’ve accumulated in between that last set of recommendations and today’s recommendations and all of them essentially point towards the fact that it is safe to provide a mixed-dose schedule,” Canada’s Chief Public Health Officer Dr. Theresa Tam told reporters on Thursday.

“We will continue to monitor this in a real life basis as vaccines are rolling out.”

For those who receive a first jab of an mRNA vaccine, it’s advised they seek the same product or use another mRNA vaccine.

The advisory panel made the specification, however, that those who have already received two doses of AstraZeneca “can rest assured that the vaccine provides good protection against infection and very good protection against severe disease and hospitalization.”

As of June 5, 2.1 million Canadians have received one shot of AstraZeneca and 15,186 people have received two doses. Of the 7,408 reports of adverse side effects following immunization since June 11 from any authorized vaccine, 1,565 are considered “serious,” such as causing a severe allergenic reaction or vaccine-induced immune thrombotic thrombocytopenia.

The head of Canada’s vaccine rollout campaign, Brig.-Gen. Krista Brodie, said there are still approximately 600,000 doses of AstraZeneca unused in Canada and it will be up to the provinces and territories to determine how best to use them.

“We continue to expect that the use of those vaccines will continue to evolve over the coming days,” Brodie said.

Dr. Tam acknowledged the frustration of Canadians who may feel misled by the body, but reiterated the challenges of working through a fluid health crisis that’s consistently changing.

“I totally recognize that this is difficult for many, but what I would say is that those who have received two doses of AstraZenca, COVISHIELD vaccine, you’ve been provided with good protection against infection,” she said.

According to records compiled by Our World in Data, 177 countries and territories have used AstraZeneca, compared with 104 for Pfizer and 54 for Moderna.

vaccine graphicMontreal-based epidemiologist Dr. Christopher Labos told CTV News Channel following the announcement there have “clearly been some missteps” in communication with regards to the use of AstraZeneca.

“The point is to give everybody two doses and when you can acknowledge that the second dose need not necessarily be the same as the first, that gives you a lot more flexibility and makes you a lot more immune to the variability of vaccine supply, so if they phrased it that way, I think it would have been a lot more reassuring to people,” he said.

The government is still aiming to receive 55 million COVID-19 vaccine doses by the end of July and  commits to being able to provide full vaccination to every Canadian that seeks it by the end of September.