Chief public health officer Doctor Theresa Tam says she expects Canadians who got the Oxford-AstraZeneca as their first dose of COVID-19 to be able to choose which vaccine they want for their second shot.
A small Spanish study on mixing and matching vaccines reported that giving a Pfizer-BioNTech shot for the second dose after AstraZeneca is safe.
It produced twice as many antibodies as a second dose of AstraZeneca.
The National Advisory Committee on Immunization is still awaiting further data from another mixing-and-matching study underway in the United Kingdom.
Tam says advice on second doses should be ready before most people are due to get the shot.
The decision could affect more than 2.1 million people vaccinated with AstraZeneca and is related mainly to safety issues for that vaccine.
Tam says there are now 21 confirmed cases of vaccine-induced thrombotic thrombocytopenia, or V-I-T-T, a rare but serious blood-clotting disorder.
Another 13 cases are under investigation.
Three women have died.
NACI advised last month that people at low risk of getting COVID-19 should get either Pfizer or Moderna.