The National Advisory Committee on Immunization (NACI) has recommended that Canadians receive the same COVID-19 vaccine for both doses.
The agency updated its vaccine guidance on May 21 to include the recommendation for second shots, as well as what should be done if a vaccine candidate is not available.
NACI said that if the vaccine that was used for someone’s first dose is not accessible, “attempts should be made” to give them a second dose of a similar type of vaccine.
So, if a person’s first dose was an mRNA vaccine, their second dose should also be an mRNA vaccine. Pfizer and Moderna are the only two mRNA vaccines approved for use in Canada.
There “is no reason to believe,” NACI said, that there would be “any additional safety issues or [a] deficiency in protection” if someone got a dose of Pfizer and then a shot of Moderna, or vice versa.
Similarly, if someone receives one dose of AstraZeneca and can’t get a second, they can have a shot of Johnson & Johnson. The two are the sole viral vector vaccines approved in Canada.
The individual must understand the risk for rare but serious blood clots, known as vaccine-induced thrombotic thrombocytopenia (VITT), that comes with the viral vector vaccines.
Cases of VITT are reportedly lower with second doses than with first, NACI said.
Despite the updated guidance, NACI clarified that there is currently no data on the interchangeability of vaccines.
More information on mixing doses, specifically for those who have received one dose of the AstraZeneca vaccine, is expected in early June.
To date, Canada has seen 1,352,121 COVID-19 cases and 25,162 virus-related deaths.