NACI recommends AstraZeneca recipients choose mRNA shot for second dose

Canadians who got a first dose of AstraZeneca and haven’t yet gotten a second dose should choose an mRNA vaccine for their second shot.

That’s the latest recommendation from the National Advisory Council on Immunization (NACI) that came down Thursday.

The preference for mRNA second shots is because there’s now an abundance of Pfizer and Moderna in Canada, and research that suggests mixing the shots could yield a better immune response.

Using an mRNA second dose also minimizes the risk of rare but dangerous blood clots known as VITT that are associated with viral vector vaccines.

Dr. Theresa Tam, Canada’s Chief Public Health Officer, said she wants people who got two shots of AstraZeneca to rest assured they made the right choice. The vaccine provides strong protection against COVID-19, and for a time, it was the most readily available vaccine when COVID-19 infections were surging during the third wave.

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NACI also recommended mRNA vaccines should be used to start an individual’s vaccine course unless that person is allergic to an ingredient in Pfizer or Moderna, or if there are no mRNA vaccines available.

In addition, NACI recommended people try and stick with the same brand of mRNA vaccine where possible. But in the event the same shot is not available, Pfizer and Moderna can be considered interchangeable.