Canada has approved the mixing and matching of COVID-19 vaccines if needed.

On June 1, the National Advisory Committee on Immunization updated its guidance to provinces and territories, saying a first shot of the AstraZeneca vaccine can be followed by a dose of the Moderna or Pfizer vaccines.

“This is good to know. It does allow us some flexibility for people who might not have access to another vaccine,” said Medical Officer of Health with the Northwestern Health Unit, Dr. Kit Young Hoon, during her weekly conference with regional media members.

“For AstraZeneca in particular, because of the concerns related to vaccine-induced thrombotic thrombocytopenia, clients are provided the option of considering a second vaccine for their second dose,” she explains.

The province decided to stop administering first doses of the AstraZeneca vaccine on May 11 due to the risk of contracting VITT, a rare disorder that affects your blood’s tendency to clot.

Nearly one million Ontarians over the age of 40 received the vaccine between March 10 and May 11.

The UK Medicines and Healthcare Products Regulatory Agency’s data previously listed the risk of blood clots from AstraZeneca’s first dose at 1 in 250,000, which was later reported at 1 in 60,000 in Ontario, when first doses were stopped.

Now, the Public Health Agency of Canada has estimated the rate of VITT to be 1 in 83,000, but as investigations continue, could reach 1 in 55,000. Internationally, VITT fatality rates range from 20 to 50 per cent. There have been five VITT-related deaths in Canada as of June 1.

NACI’s updated guidance comes after more studies from Germany and Spain. Due to the risk of VITT, several European countries including Germany and Spain, Denmark, Finland, France, Norway and Sweden began offering the Pfizer and Moderna vaccines as second doses, without substantial risk.

NACI has also recommended that anyone who received a first dose of the Pfizer of Moderna vaccines receive the same vaccine for their second dose, if available. Although, the two are interchangeable.

“We would be aiming to provide individuals with the same vaccine if it is available,” adds Young Hoon. “At this time, both Pfizer and Moderna are available in our catchment area. We are aiming for people to get the same vaccine they got the first time, for their second dose.”

Both the Pfizer and Moderna vaccines use messenger RNA technology, using RNA encoded with the piece of the COVID-19 virus known as the spike protein. The mRNA then trains the body to fight off a COVID-19 infection.

As of June 1, the federal government reports that nearly 13.5 million residents, 35 per cent, received Pfizer for their first dose of the vaccine, with 3.5 million receiving Moderna, representing 9 per cent.

AstraZeneca and Johnson & Johnson operate as viral vector vaccines, which takes a cold virus and modifies it so it can’t reproduce itself, before adding the COVID-19 spike protein. When injected, it provokes the body to develop infection-fighting antibodies and cells to fight the virus.

As of June 1, Canada says about 1.6 million residents received the AstraZeneca vaccine, 4.45 per cent, with under 500,000 receiving the COVISHIELD vaccine.