Alberta Health says the province has stopped administering first doses of the AstraZeneca-Oxford COVID-19 vaccine in favour of other brands because supply of the vaccine is expected to become scarce.
Alberta's existing supply of AstraZeneca will be used as second doses, the provincial health department confirmed on Tuesday.
Dr. Deena Hinshaw, Alberta's chief medical officer of health, said it's unclear when Alberta will get additional shipments of AstraZeneca, and that lack of supply prompted provincial health officials to alter the immunization strategy.
The remaining supply of AstraZeneca will also be reserved for people who have a medical condition that makes them ineligible for messenger RNA vaccines, also known as mRNA vaccines, which are produced by Pfizer-BioNTech and Moderna.
"Based on global supply challenges, we do not know when we will get additional supply," Hinshaw said in a statement on Twitter.
"That's why we are making the prudent move – saving the remaining 8,000 doses for those who have a contraindication to an mRNA vaccine, or for second doses."
Mix and match?
It's unclear whether those who received AstraZeneca can be offered a different vaccine for their second dose, but Hinshaw says health officials are reviewing the research.
A study of a "mismatched" vaccine regimen is underway in the U.K.
"Some people have asked if they will receive an mRNA vaccine for their second dose instead of AstraZeneca," Hinshaw wrote Tuesday.
"We are reviewing emerging evidence in the U.K. and other places as we speak to decide the best path forward.
"I want to reassure Albertans that AstraZeneca is a good vaccine that will protect you against severe outcomes. This decision reflects us adapting to the supply and the emerging evidence, which we will keep on doing."
More than 250K doses administered
Alberta has administered roughly 255,000 first doses of AstraZeneca and 2,200 second doses, Alberta Health said in a statement to CBC News on Tuesday.
The remaining supply accounts for about 8,400 doses, the statement said.
Alberta Health said it continues to receive shipments of the Pfizer-BioNTech and Moderna vaccines in large and consistent shipments. More than 236,000 doses are arriving this week alone.
More than 318,841 Albertans have been fully immunized with two doses of COVID-19 vaccine. As of Sunday, about 35.7 per cent of Alberta's population had received at least one dose.
Use of the AstraZeneca vaccine has been under added scrutiny in recent weeks, particularly after Canada's panel of vaccine experts recommended that people who aren't at high risk of contracting COVID-19 may want to wait to get a dose of the Pfizer or Moderna.
The AstraZeneca vaccine has been linked to vaccine-induced immune thrombotic thrombocytopenia (VITT), an extremely rare blood clot disorder. To date, Alberta has reported two cases of VITT and one death.
The currently reported frequency of blood clots from the AstraZeneca vaccine ranges from one in 25,000 doses in Norway to one in one million doses in the U.K., Alberta Health said.
The federal government confirmed last week that it will continue to procure AstraZeneca, and that well over a million doses are expected to arrive between now and the end of June.