British Columbians who received the AstraZeneca-Oxford COVID-19 vaccine as their first dose will likely be able to choose whether they want their second vial filled with the same vaccine, the province's top doctor has said.
Provincial Health Officer Dr. Bonnie Henry says as shipments of the Pfizer-BioNTech and Moderna vaccines increase, switching up the type of shot for the second dose is a possibility, as long as it is proven to be safe and effective.
"I expect people will have a choice," she told Stephen Quinn, host of CBC's The Early Edition, on Tuesday morning.
Henry said she is closely watching research being done now in the United Kingdom, where about 60 per cent of people were given AstraZeneca for their first shot. Researchers at Oxford University launched a study in early February to explore the possible benefits of alternating different COVID-19 vaccines.
Henry's comments come as the AstraZeneca vaccine faces continued scrutiny in jurisdictions around the world after it was linked to vaccine-induced immune thrombotic thrombocytopenia (VITT), an extremely rare blood clot disorder. Some provinces are considering pausing the vaccine's use altogether.
Henry reiterated on Tuesday that the vaccine is safe — and suggested that following a dose of AstraZeneca with an mRNA vaccine like Pfizer or Moderna could perhaps be even more effective in fighting the coronavirus than two doses of the same shot.
Vaccines like AstraZeneca force an immune response from the harmless version of the virus, while mRNA vaccines like Pfizer and Moderna give immune cells instructions to make the COVID spike protein and produce antibodies.
"AstraZeneca probably stimulates what we call the cell mediated immunity, or the memory cells, a little bit better than the mRNA. So I think it's likely that if you get a single dose of AstraZeneca and a booster dose with mRNA, you might get the best of both worlds," Henry said.
Henry said some of the safety data from the U.K. study has been reassuring so far and she expects to see more details on the efficacy of combining vaccines in the next couple of weeks.
Well-stocked with shots
Millions more mRNA vaccine shots are expected in Canada over the coming weeks — Pfizer alone will deliver two million shots each week in May before ramping up to 2.4 million a week next month — meaning there should be enough supply to vaccinate AstraZeneca recipients with a second dose of a second product.
"We're moving into a place now where we can use the [mRNA]. They're the ones that we're going to have more of in the next little while," said Henry.
According to the federal government, B.C. had received 2,657,520 total vaccine doses as of May 11, of which 315,000 vials were AstraZeneca and the bulk were the two mRNA vaccines.
In a statement to CBC Tuesday afternoon, the provincial health ministry said AstraZeneca is safe and effective but that B.C. is not expecting any additional supply in the short term and that the vaccination effort will continue primarily with Pfizer and Moderna.
"We do expect to receive additional AstraZeneca to ensure everyone can receive their second dose, or if they prefer to receive AstraZeneca over a mRNA vaccine or have contraindications to mRNA, like an allergic reaction," said the ministry.
Henry described AstraZeneca as "the vaccine that can't get a break" due to the controversy around it.
She said it has been a very important component of B.C.'s vaccine program, particularly in March and April when cases were rising and there were limited amounts of mRNA vaccines on hand.
"People need to be reassured that it's a good thing to have, particularly at the period of time that we needed it," she said.
Premier John Horgan, speaking to reporters Tuesday afternoon, said he has no qualms about getting a second shot of AstraZeneca.
"My wife and I were immunized with AstraZeneca. I fully expect to get a second shot when I'm advised that I'm ready to go and I know my spouse feels the same way," said the premier.
Dr. Theresa Tam, Canada's chief public health officer, said last week the current guidance is for AstraZeneca recipients to get a second dose of the same product, but the National Advisory Committee on Immunization is reviewing the Oxford research on mixing AstraZeneca with an mRNA shot.
According to Health Canada data, around 1.7 million AstraZeneca doses have been administered in Canada as of April 24.