18 June 2021
• The National Advisory Committee on Immunization (NACI) recommendations on the use of a different mRNA COVID-19 vaccine product to complete a COVID-19 vaccine series started with an mRNA COVID-19 vaccine is being followed in Ontario: o NACI recommends that, if readily available*, the same mRNA COVID-19 vaccine product should be offered for the subsequent dose in a vaccine series started with an m. [...] o If only an alternate mRNA vaccine product is available at the time of the second dose, a different mRNA vaccine can be used for the 2nd dose. [...] • Where a different product is used to complete the vaccine series, the earliest interval at which the vaccine can be given is the Health Canada product monograph authorized interval of the vaccine used for the first dose. [...] The spike protein encoded by either of the authorized mRNA vaccines is stabilized in the same manner, although other vaccine components like the lipid nanoparticle and the mRNA sequence may be different. [...] What do we know about the importance of getting the second dose when it is offered? • It is essential to complete the vaccine series to boost the initial immune response and because it is anticipated to provide protection in the longer term.