Pfizer, Moderna vaccines now preferred second dose for AstraZeneca recipients: NACI

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

On June 1, NACI 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 NACI first looked at mixed vaccine schedules, new evidence is starting to emerge suggesting immune responses are better when a first dose of the AstraZeneca vaccine is followed by an mRNA vaccine as a second dose,” said NACI vice-chair Dr. Shelley Deeks, in the new guidance documents.

NACI 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 NACI 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 favour 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.

One of those studies from Germany’s Saarland University, published early data Wednesday saying giving Pfizer as the second dose after AstraZeneca, or two doses of Pfizer only, generated far more antibodies and T cells as two doses of AstraZeneca.

The mixed-dose schedule was slightly better than two doses of Pfizer at producing the neutralizing antibodies and killer T cells that are critical to preventing infection or serious illness.

Quebec was not moving to follow NACI’s advice. Health Minister Christian Dubé, who got two doses of AstraZeneca himself, said Quebec is still saying people can opt for a mixed schedule or two doses of AstraZeneca, depending on their personal choice.

Almost 25 million Canadians have now received at least one dose of vaccine, and almost six million are now fully vaccinated.

As of June 5, 2.1 million people had received one dose of AstraZeneca, and 15,186 had received two doses.

Canada has received 56 reports of blood clots following an AstraZeneca vaccination, and 38 are now confirmed as vaccine-induced thrombotic thrombocytopenia, or VITT.

There are no further shipments of AstraZeneca currently scheduled, but there are about 600,000 doses still left from previous deliveries.

There are 14 million doses of Pfizer-BioNTech and Moderna being delivered this week and next, including a donation of one million doses of Moderna’s COVID-19 vaccine from the United States that was to arrive in Canada Thursday night.

The donation won’t cost Canada anything, and will be on top of the 44 million doses Canada has purchased directly from Moderna.

It comes less than a week after Canada promised to donate 13 million doses to the COVAX vaccine-sharing alliance, which will entirely come from the remaining share of doses Canada had purchased from COVAX itself.

Canada has been heavily criticized for buying three times as many doses of COVID-19 vaccine than it needs and not sharing any doses from its own direct purchase agreements with vaccine makers. The World Health Organization has made repeated pleas for wealthier countries to share more doses with developing countries, some of whom have vaccinated very few people at all.

Canada expects to have fully vaccinated 75 per cent of all eligible Canadians — everyone over the age of 12 — by the end of July, and has administered 78 doses for every 100 Canadians. Across Africa, nations have given out three doses for every 100 people.

“Taking vaccines at a time when we are nearing complete vaccination when many developing countries are so far behind makes Canada a vaccine hoarder and leaves Canadians vulnerable to dangerous variants,” said NDP health critic Don Davies.

This report by The Canadian Press was first published June 17, 2021.

Mia Rabson, The Canadian Press