First dose of AstraZeneca can be followed by second jab of Pfizer/Moderna – NACI updates recommendations on mixing vaccines

Canada’s National Advisory Committee on Immunization (NACI) has updated its recommendations to allow mixing of mRNA and conventional COVID-19 vaccines for first and second doses after studying safety data gathered in other countries.

If readily available, the same mRNA COVID-19 vaccine product should be offered for the subsequent dose in a vaccine series started with an mRNA COVID-19 vaccine, according to a summary of the updated NACI recommendations posted online.

However, when the same mRNA COVID-19 vaccine product is not readily available, or is unknown, another mRNA COVID-19 vaccine product recommended for use in that age group can be considered interchangeable and should be offered to complete the vaccine series, NACI states.

The federal advisory panel is also recommending that 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.

NACI says its recommendation to offer mRNA as the second dose is based on expert opinion and on the risk of VITT after the first and second doses of the AstraZeneca/COVISHIELD vaccine, the possibility of increased short-term reactogenicity with a mixed schedule and emerging data on immunogenicity of a mixed schedule of the AstraZeneca followed by the Pfizer-BioNTech vaccine.

NACI recommendations are “in line with basic principles of vaccinology” and “it is expected that combining different COVID-19 vaccines that induce an immune response against the SARS-CoV-2 spike protein will lead to a robust immune response,” advisory body said

Canada is anticipating large supplies of mRNA vaccines in the summer months that will be sufficient to complete the second dose in all age groups for whom immunization is
recommended, NACI added.



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