Vaccine Mix and Match

This week the National Advisory Committee on Immunization (NACI) updated their recommendations on the interchangeability of the COVID-19 vaccines to allow for mixing of products between first and second doses.

These recommendations are based on emerging evidence from Spain, Germany and the UK which suggest that mixed vaccine schedules are safe and effective at preventing COVID-19 infections. They also factor into the risk of vaccine-induced immune thrombotic thrombocytopenia associated with the AstraZeneca vaccine, and the wide availability of mRNA vaccines (Pfizer/Moderna) which are not associated with this risk. NACI reminded Canadians this practice is quite common and historically ‘similar vaccines from different manufacturers are routinely used interchangeably’.

What this means for Canadians is that those who received a first dose of:

• The AstraZeneca vaccine can receive either a second dose of it or an mRNA vaccine

• An mRNA vaccine should be offered the same mRNA vaccine for their second dose. Another mRNA vaccine would be considered interchangeable if the initial vaccine was not readily available.

Additional studies looking at the mixed vaccine schedules are currently ongoing, and we look forward to seeing the results of these trials as they become available to see how they will guide decision making as we navigate best practices moving forward.

- Courtney