Canada: Pfizer, Moderna preferred 2nd dose after AstraZeneca

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Canada's National Advisory Committee on Immunization said Thursday people who got the AstraZeneca vaccine as their first dose should get Pfizer-BioNTech or Moderna for their second shot.

On June 1, committee had said AstraZeneca recipients “could" get Pfizer or Moderna for their second shot if they wanted, but Thursday went further to say an mRNA vaccine was the ”preferred" choice.

Since the advisory committee "first looked at mixed vaccine schedules, new evidence is starting to emerge suggesting immune สล็อต ฝาก-ถอน true wallet responses are better when a first dose of the AstraZeneca vaccine is followed by an mRNA vaccine as a second dose," said its vice-chair Dr. Shelley Deeks, in the new guidance documents.

The committee also updated its previous recommendation that people at high risk of exposure to, or serious illness from, COVID-19, could opt to get AstraZeneca rather than waiting for Pfizer or Moderna. Now it says everyone should always get the mRNA vaccines first, unless they are allergic to them.

Deeks said the advice is based on the growing supply of Pfizer and Moderna, and the risk of vaccine-induced blood clots associated with AstraZeneca. But she is still trying to reassure people who got one or two doses of AstraZeneca's vaccine that they are nevertheless well protected.

“Anyone who has already received two doses of AstraZeneca/Covishield can rest assured that they are protected, particularly against severe illness,” she said. "There is no need for a third dose at this time."

Dr. Theresa Tam, the chief public health officer of Canada, said the new evidence in favor of mixing different types of vaccines included four studies in Germany.

"It's really the immunogenicity, that immune response, after that mixed-dose schedule that's resulted in NACI updating this recommendation, because all the accumulated studies essentially suggest that immune response is a better response," said Tam at a news conference in Ottawa.