Archived 12: Summary of NACI rapid response of June 1, 2021

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This is an archived version. Please refer to current COVID-19 vaccine pages:

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Mixed COVID-19 vaccine schedules

To see the rapid response, please visit NACI rapid response: Interchangeability of COVID-19 vaccines.

What you need to know


"We know that the question of which vaccine will be used for second doses, in particular for individuals who had received the AstraZeneca/COVISHIELD vaccine as their first dose, has been a question for many people these last few months. NACI has seen additional data on the safety of using mixed COVID-19 vaccine schedules and NACI has also seen some data on the immune response following this mixed schedule. Based on that evidence, but also on the risk of the rare but serious adverse event called VITT that is associated with the viral vector vaccines, we are recommending that someone who received a first dose of the AstraZeneca/COVISHIELD vaccine may receive an mRNA vaccine for their second dose."

"The Committee strongly recommends that if one mRNA vaccine was used for the first dose, the other mRNA vaccine can be used as the second dose if needed. Second doses are important for more robust and long-term protection. These NACI recommendations on mixed schedules will provide flexibility for provinces and territories in the move towards second doses."
- Dr. Caroline Quach-Thanh, NACI Chair

"The public health community values the advice of Canada's National Advisory Committee on Immunization in supporting the development of COVID-19 immunization policies based on the latest scientific evidence. NACI continues to be a key partner in efforts to optimize the use of vaccines as part of Canada's pandemic response. This rapid response on the interchangeability of authorized COVID-19 vaccines will guide decision-making by provinces and territories as we continue to roll-out Canada's COVID-19 vaccination campaign."
- Dr. Theresa Tam, Chief Public Health Officer of Canada

NACI forward agenda

NACI continues to actively review emerging evidence on COVID-19 vaccines. Upcoming recommendation may include new advice on:

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