First AstraZeneca COVID-19 vaccine can be followed by Pfizer or Moderna, Canadian advisory group says - The Globe and Mail

A pharmacist prepares the Pfizer-BioNTech COVID-19 mRNA vaccine at a clinic in Halifax in March.

Andrew Vaughan/The Canadian Press

People who received a first shot of the Oxford-AstraZeneca COVID-19 vaccine can receive a second shot from either Pfizer or Moderna, the federal vaccine advisory panel said on Tuesday.

In an updated statement, the National Advisory Committee on Immunization, (NACI) said it was giving a discretionary recommendation that people who received AstraZeneca can receive either the Pfizer-BioNTech or Moderna vaccines for their second shot. The same recommendation is being given for a vaccine made in India, called Covishield, which is comparable to AstraZeneca.

Viral vector vaccines, like those from AstraZeneca, Covishield, and Johnson & Johnson, are linked to a rare blood-clot condition that mRNA vaccines, like those from Pfizer and Moderna, are not connected to. The risk of that rare side effect is one of several factors leading to the advice that vaccines can be mixed. The changing advice is also being made because Canada has the luxury of relying on mRNA shots for its mass vaccination campaign and because emerging data shows the body still mounts a robust immune response when vaccines are mixed.

“Either AstraZeneca/COVISHIELD COVID-19 vaccine or an mRNA COVID-19 vaccine product may be offered for the subsequent dose in a vaccine series started with an AstraZeneca/COVISHIELD COVID-19 vaccine,” the committee said in a statement published to its website.

“The previous dose should be counted, and the series need not be restarted.”

On mixing mRNA doses, NACI said if the first dose came from Pfizer or Moderna the same vaccine should be used for the second dose when it’s “readily available.” But if the same vaccine is not available, then the alternative mRNA vaccine should be used for a second dose.

Members of the NACI were not part of a news conference about the advice on Tuesday. Instead, Chief Public Health Officer Theresa Tam and her deputy, Howard Njoo, answered questions on the latest recommendations.

“NACI recommendations are based on the strength of emerging evidence over top of a strong foundation of many decades of experience with vaccine programs in Canada,” Chief Public Health Officer Theresa Tam said Tuesday.

“This advice provides provinces and territories with safe and effective options to manage their vaccine programs.”

Quebec already gives people who received a first dose of AstraZeneca the option of an mRNA vaccine for their second shot. On Monday, though, Manitoba gave stronger advice, saying it recommends people who received a first shot from AstraZeneca get an mRNA vaccine for their second dose.

“A Spanish study has been released that showed that people who received a second dose of an mRNA vaccine, after AstraZeneca, had a good immune response,” Joss Reimer, medical lead for Manitoba’s vaccine rollout, said on Monday. “This is consistent with what we have seen in vaccines for other diseases as well. We’ve seen that changing products in between doses for almost every other vaccine still results in good effectiveness. And ultimately that’s what we’re after.”

The blood clot syndrome is called vaccine-induced immune thrombotic thrombocytopenia (VITT). The rate of the syndrome, while still rare, has increased as more data is released. Last week NACI said the rate in Canada is estimated to be between one per 26,000 and one per 100,000 people vaccinated with a first dose of AstraZeneca. As of May 12, the federal public health agency has estimated the rate of VITT in Canada to be one in 83,000 doses administered, however the agency has said the rate could be as high as one in 55,000.

“With increased observation times, VITT rates have generally increased,” NACI said in its statement on Tuesday.

Provinces stopped using AstraZeneca for first shots in mid-May amid growing concerns of a rare but serious blood clot side effect linked to the vaccine and as supply for the vaccine became more uncertain. However some, like Ontario and Quebec are still administering the vaccine for second doses.

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First AstraZeneca COVID-19 vaccine can be followed by Pfizer or Moderna, Canadian advisory group says - The Globe and Mail
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