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A pilot study at Dalhousie University has shown that mixing two different COVID-19 vaccines can be highly effective in generating the neutralizing antibodies necessary to fight the communicable disease and boost immunity.

Dr. Chris Richardson, along with students and members of the Canadian Center of Vaccinology at Dalhousie, studied the antibodies produced in two 66-year-old subjects who received two different vaccines against SARS-CoV-2, the virus that causes COVID-19. They were first vaccinated with AstraZeneca, followed 33 days later with a second dose, or booster, of the Pfizer-BioNTech vaccine.

Researchers collected serum samples 25 days after the primary vaccination and 13 days after the secondary Pfizer vaccination. Both subjects showed increased antibodies against the spike protein of the COVID-19 virus following immunizations, especially after the second booster. The levels of these protective antibodies approached those of a convalescent patient known to have an excellent response against the COVID-19 virus after surviving the disease.

The antibodies also neutralized a safe model virus, which contains the COVID-19 spike protein and green fluorescent protein from jellyfish. When cultured kidney cells were infected with the model virus, they glowed in the dark under UV light. That green light dimmed following the AstraZeneca and Pfizer vaccines, and the antibodies in the serum inhibited infection of the cultured cells.

The findings come as Canada’s National Advisory Committee on Immunization announced that people who received the AstraZeneca vaccine as their first shot can now get the Pfizer-BioNTech or Moderna for their second.

Dr. Richardson, a professor in the Department of Microbiology and Immunology, is available to discuss the findings and how they validate both the value of the Pfizer vaccine in boosting immunity after an initial AstraZeneca inoculation, and the decision in some jurisdictions to reduce the time between vaccinations.

The results of the pilot study will be published in the Journal of Infection in Developing Countries.

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Media contact:
Alison Auld
Senior Research Reporter
Dalhousie University
Cell: 1-902-220-0491
Email: alison.auld@dal.ca