All provinces stopped using AstraZeneca for first doses back in May. Many have continued to use it as a booster injection. A second dosage of an mRNA product is currently considered “recommended” by the National Advisory Committee on Immunization.
“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 associated with viral vector vaccines.”
According to NACI, evidence from German research suggests that combining one AstraZeneca dose with a second dose of a Pfizer vaccination can create “a potentially greater immune response, including against variations of concern,” than two AstraZeneca doses alone.
For more information to https://www.canada.ca/en/public-health/services/immunization/national-advisory-committee-on-immunization-naci/recommendations-use-covid-19-vaccines/summary-statement-june-17-2021.html