Moderna and Pfizer Are Preferred as the Second Dose After AstraZeneca

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Image Credit – TOI


The National Advisory Committee on Immunization of Canada has said that people who got the AstraZeneca vaccine as their first dose should get Moderna or Pfizer-BioNTech for their very important second shot.

On the 1st of June, the committee has said that AstraZeneca recipients could get Moderna or Pfizer for their second shot if they want it and on Thursday they went further to say an mRNA vaccine was the preferred choice.

The advisory committee has first looked at mixed vaccine schedules as 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 as has been said by Dr. Shelley Deeks, the vice-chairman in the new guidance documents.

The committee also went on to update its previous recommendation that people who are at very high risk of exposure to or serious illness from, Covid-19, can opt for AstraZeneca rather than waiting for Moderna or Pfizer. But now it has been said that everyone should get the mRNA vaccine first unless they are allergic to them.

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

She further added that anyone who has already received two doses of Covishield/AstraZeneca can rest assured that they are protected particularly against severe diseases. Dr. Theresa Tam, the chief public health officer of Canada has said that at this time there is no need for a third dose and also said that the new evidence is in favor of mixing different types of vaccines included four studies in Germany.

Tam was speaking at a news conference in Ottawa where she said that it is the immune response, the immunogenicity after that mixed dose schedule that has resulted in NACI updating this recommendation because all the accumulated studies have essentially suggested that immune response is a better response.

One of those studies from the Saarland University of Germany has published early data on Wednesday saying giving Pfizer as the second dose after AstraZeneca or two doses of Pfizer only generated far more T cells and antibodies as two doses of AstraZeneca.

Almost 25 million Canadians have now received at least one dose of vaccine and almost 6 million are now fully vaccinated. As of 5th June, 2.1 million people had received one dose of AstraZeneca, and two doses of the same vaccine are received by 15,186.

Currently, there are no further shipments of AstraZeneca that are scheduled but there are about 600,000 doses still left from previous deliveries. There are 14 million doses of Moderna and Pfizer-BioNTech that are being delivered this week and another 1 million doses will arrive.