National Advisory Committee on Immunization (NACI) is now recommending that individuals who received a single dose of the AstraZeneca COVID-19 vaccine be given an mRNA vaccine, Pfizer-BioNTech or Moderna vaccine, for their second dose.
"An mRNA vaccine is now preferred as the second dose for individuals who received a first dose of the AstraZeneca/COVISHIELD vaccine, based on emerging evidence of a potentially better immune response from this mixed vaccine schedule and to mitigate the potential risk of VITT [vaccine-induced immune thrombotic thrombocytopenia] associated with viral vector vaccines," the recommendation from NACI reads.
Despite this guidance, the committee is also signalling that Canadians who have been fully vaccinated with AstraZeneca should "rest assured that the vaccine provides good protection against infection and very good protection against severe disease and hospitalization."
"The emerging evidence suggesting better immune responses when a first dose of the AstraZeneca vaccine is followed by a second dose of the Pfzier-BioNTech or Moderna mRNA vaccines," Dr. Theresa Tam, Canada's chief public health officer said at a press conference on Thursday.
"NACI’s earlier recommendation that people who wanted earlier vaccination could receive a viral vector vaccine rather than wait for mRNA reflected supply of mRNA vaccines at the time."
Canadians who have received the AstraZeneca vaccine took to social media to express some concerns about the changes.
But some continue to share that they are comfortable getting two doses of AstraZeneca.
Dr. Tam stressed that NACI's guidance has evolved with emerging evidence, while recognizing that it can be difficult to understand and catch up to the changes being made.
Canadians with AstraZeneca vaccine facing issues travelling to U.S.
This announcement also comes as COVID-19 protocol in the U.S. dictates that individuals will not be able to attend Springsteen on Broadway if vaccinated with a vaccine not authorized by the FDA, which includes AstraZeneca.