Canada: mRNA Covid-19 vaccines preferred choice for both jabs

Updated on Jun 18, 2021 02:25 PM IST
The immunisation committee said that doses can be mixed, with those receiving AZ as the first dose now being given an mRNA vaccine as the second dose, such as Pfizer-BioNTech or Moderna.
A patient receives a Covid-19 vaccine at a clinic in Ottawa, Ontario, Canada. (REUTERS)
A patient receives a Covid-19 vaccine at a clinic in Ottawa, Ontario, Canada. (REUTERS)
ByAnirudh Bhattacharyya I Edited by Amit Chanda

Canadian health authorities have announced fresh guidelines stating that mRNA Covid-19 vaccines are now the “preferred” jabs for both the first and second dose even if the first was administered using AstraZeneca (AZ), which is manufactured in India under the Covishield brand name.

These were among the updated recommendations issued by the National Advisory Committee on Immunisation (NACI).

In its recommendations, NACI said the mRNA vaccines should be preferred unless “is inaccessible or there is a contraindication, for example, an allergy to an mRNA vaccine or its components”. Only in the latter circumstances should a viral vector vaccine, like AZ, be offered.

It also endorsed vaccine interchangeability, basically that doses can now be mixed with those receiving the first dose of AZ now being given the second dose as an mRNA vaccine such as those from Pfizer-BioNTech or Moderna.

NACI said that “emerging evidence” from studies in Germany have suggested a “potentially better immune response, including against variants of concern, when a first dose of the AstraZeneca vaccine is followed by a second dose of the Pfizer-BioNTech mRNA vaccine, compared to two doses of the AstraZeneca vaccine”. Similarly, it said, evidence suggested that such mixing “has a good safety profile”.

However, those who received their first jab of AZ can still opt for the same to complete the vaccination series. “Getting two doses of the AstraZeneca/Covishield vaccine provide good protection against Covid-19 disease,” NACI said.

“NACI is also recommending that for anyone who received a first dose of AstraZeneca/Covishield, an mRNA vaccine is now preferred for the second dose. 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,” NACI chairperson Dr Shelley Deeks said.

These announcements have followed continued concern over a rare side-effect of the AZ vaccine, vaccine-induced immune thrombotic thrombocytopenia or VITT, which can lead to blood clotting with low platelet counts, and can sometimes prove fatal if not treated in time.

However, adverse reactions to mRNA vaccines are also being looked at as NACI said rare cases of myocarditis (inflammation of the heart muscle) and pericarditis (inflammation of the heart lining) following such vaccination “have been reported in Canada and internationally, including in Israel and the United States”.

“No clear association between myocarditis/pericarditis and mRNA Covid-19 vaccines has been established in Canada. This may change as more evidence emerges and Canada administers more second doses of mRNA vaccines,” the NACI added, though it also said cases have so far been “mild and resolved with medical treatment”.

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