With AstraZeneca delays, and 36 million doses of Pfizer and Moderna scheduled to come, mixing for potentially hundreds of thousands of people may become unavoidable
Original author: Sharon Kirkey
Published: May 5, 2021
In the midst of a variant-driven third wave, Canada’s beleaguered vaccine advisory panel is considering whether to endorse mixing vaccine doses.
With supplies of AstraZeneca mostly exhausted, and future delivery dates uncertain, the National Advisory Committee on Immunization is weighing up options for swapping second, booster doses.
There is no reason why people who have had one dose of AstraZeneca shouldn’t receive a second dose of the same vaccine, the panel said Monday, despite reiterating its earlier stance that mRNA vaccines — Pfizer-BioNTech and Moderna — are “preferred” over the AstraZeneca and Johnson & Johnson shots, due to a remote risk of an unusual type of blood clotting complication.
But with delays in AstraZeneca supplies, and 36 million doses of Pfizer and Moderna scheduled to be delivered over the next two months, mixing for some people, potentially hundreds of thousands, may become unavoidable.
The panel’s co-chair has already said that Pfizer and Moderna shots are similar enough that people who receive the Pfizer shot could receive Moderna for their second dose, and vice versa. “Let’s say you run out of Pfizer’s vaccine because you’ve administered all your doses, or you don’t know what your patient had at first … this eases up the complexity,” Dr. Caroline Quach-Thanh told the Canadian Medical Association Journal in December. Quebec has already announced it would substitute the second Moderna dose with a Pfizer dose, if necessary, to fully vaccinate long-term care residents as soon as possible.
But the vaccine advisory group is also considering combining Pfizer or Moderna with AstraZeneca. The panel said it will make recommendations about “next schedules” once it receives more data.
All three vaccines require two doses. Johnson & Johnson is a one-shot jab.
Pfizer and Moderna, both mRNA-based vaccines, deliver genetic instructions that tell the body’s cells to start producing and pushing out harmless pieces of the spike protein found on the surface of the virus that causes COVID-19. The cells make the protein piece, triggering an immune response and priming the immune system to attack the virus should the person later becomes infected with the virus. Tiny droplets of fat called lipid nanoparticles deliver the mRNA into human cells.
AstraZeneca and the J & J vaccine use a different approach. The AstraZeneca shot, developed with the University of Oxford, uses a weakened version of a common cold virus to introduce coronavirus proteins into cells, triggering the body to generate an immune response.