Very mixed message regarding mixing and matching vaccines. From your link:
"Ontario continues to follow the advice of the National Advisory Committee on Immunization (NACI), which recommends that it is safe to mix vaccines based on studies from the UK, Spain and Germany that have found that mixing vaccines is safe and produces a strong immune response," Luis said.
...
"It's a little bit of a dangerous trend here. We are in a data-free, evidence-free zone as far as mix and match," Swaminathan said."
AstraZeneca was pushed at Canadians in specific older-adult age groups as "it's better than nothing" and "nothing else is available."
Between first and second vaccinations, the gov't announced the AstraZeneca vaccine withdrawn due to health risks. Everyone who received the AstraZeneca shot first was told to have a Pfizer or Moderna vaccine second. Mixing and matching by design, recommended by the federal government.
In Canada, there was a Pfizer shortage in June, 2021, so people who could not find the Pfizer vaccine were told to get the Moderna vaccine.
Essentially, many people who received AstraZeneca or Pfizer did a
mix and match for the second shot.